Microbiology Info.com

Glycolysis Explained in 10 Easy Steps

Glycolysis is the metabolic process that serves as the foundation for both aerobic and anaerobic cellular respiration. In glycolysis, glucose is converted into pyruvate. Glucose is a six- memebered ring molecule found in the blood and is usually a result of the breakdown of carbohydrates into sugars. It enters cells through specific transporter proteins that move it from outside the cell into the cell’s cytosol. All of the glycolytic enzymes are found in the cytosol.

The overall reaction of glycolysis which occurs in the cytoplasm is represented simply as:

C 6 H 12 O 6 + 2 NAD + + 2 ADP + 2 P —–> 2 pyruvic acid, (CH 3 (C=O)COOH + 2 ATP + 2 NADH + 2 H +

Step 1: Hexokinase

The first step in glycolysis is the conversion of D-glucose into glucose-6-phosphate. The enzyme that catalyzes this reaction is hexokinase.

Here, the glucose ring is phosphorylated. Phosphorylation is the process of adding a phosphate group to a molecule derived from ATP. As a result, at this point in glycolysis, 1 molecule of ATP has been consumed.

The reaction occurs with the help of the enzyme hexokinase, an enzyme that catalyzes the phosphorylation of many six-membered glucose-like ring structures. Atomic magnesium (Mg) is also involved to help shield the negative charges from the phosphate groups on the ATP molecule. The result of this phosphorylation is a molecule called glucose-6-phosphate (G6P), thusly called because the 6′ carbon of the glucose acquires the phosphate group.

Step 2: Phosphoglucose Isomerase

The second reaction of glycolysis is the rearrangement of glucose 6-phosphate (G6P) into fructose 6-phosphate (F6P) by glucose phosphate isomerase (Phosphoglucose Isomerase).

The second step of glycolysis involves the conversion of glucose-6-phosphate to fructose-6-phosphate (F6P). This reaction occurs with the help of the enzyme phosphoglucose isomerase (PI). As the name of the enzyme suggests, this reaction involves an isomerization reaction.

The reaction involves the rearrangement of the carbon-oxygen bond to transform the six-membered ring into a five-membered ring. To rearrangement takes place when the six-membered ring opens and then closes in such a way that the first carbon becomes now external to the ring.

Step 3: Phosphofructokinase

Phosphofructokinase, with magnesium as a cofactor, changes fructose 6-phosphate into fructose 1,6-bisphosphate.

In the third step of glycolysis, fructose-6-phosphate is converted to fructose- 1,6- bi sphosphate (FBP). Similar to the reaction that occurs in step 1 of glycolysis, a second molecule of ATP provides the phosphate group that is added on to the F6P molecule.

The enzyme that catalyzes this reaction is phosphofructokinase (PFK). As in step 1, a magnesium atom is involved to help shield negative charges.

Step 4: Aldolase

The enzyme Aldolase splits fructose 1, 6-bisphosphate into two sugars that are isomers of each other. These two sugars are dihydroxyacetone phosphate  (DHAP) and glyceraldehyde 3-phosphate (GAP).

This step utilizes the enzyme aldolase, which catalyzes the cleavage of FBP to yield two 3-carbon molecules. One of these molecules is called glyceraldehyde-3-phosphate (GAP) and the other is called dihydroxyacetone phosphate (DHAP).

Step 5: Triosephosphate isomerase

The enzyme triosephosphate isomerase rapidly inter- converts the molecules dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP). Glyceraldehyde phosphate is removed / used in next step of Glycolysis.

GAP is the only molecule that continues in the glycolytic pathway. As a result, all of the DHAP molecules produced are further acted on by the enzyme Triosephosphate isomerase (TIM), which reorganizes the DHAP into GAP so it can continue in glycolysis. At this point in the glycolytic pathway, we have two 3-carbon molecules, but have not yet fully converted glucose into pyruvate.

Step 6: Glyceraldehyde-3-phosphate Dehydrogenase

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) dehydrogenates and adds an inorganic phosphate to glyceraldehyde 3-phosphate, producing 1,3-bisphosphoglycerate.

In this step, two main events take place: 1) glyceraldehyde-3-phosphate is oxidized by the coenzyme nicotinamide adenine dinucleotide (NAD); 2) the molecule is phosphorylated by the addition of a free phosphate group. The enzyme that catalyzes this reaction is glyceraldehyde-3-phosphate dehydrogenase (GAPDH).

The enzyme GAPDH contains appropriate structures and holds the molecule in a conformation such that it allows the NAD molecule to pull a hydrogen off the GAP, converting the NAD to NADH. The phosphate group then attacks the GAP molecule and releases it from the enzyme to yield 1,3 bisphoglycerate, NADH, and a hydrogen atom.

Step 7: Phosphoglycerate Kinase

Phosphoglycerate kinase transfers a phosphate group from 1,3-bisphosphoglycerate to ADP to form ATP and 3-phosphoglycerate.

In this step, 1,3 bisphoglycerate is converted to 3-phosphoglycerate by the enzyme phosphoglycerate kinase (PGK). This reaction involves the loss of a phosphate group from the starting material. The phosphate is transferred to a molecule of ADP that yields our first molecule of ATP. Since we actually have two molecules of 1,3 bisphoglycerate (because there were two 3-carbon products from stage 1 of glycolysis), we actually synthesize two molecules of ATP at this step. With this synthesis of ATP, we have cancelled the first two molecules of ATP that we used, leaving us with a net of 0 ATP molecules up to this stage of glycolysis.

Again, we see that an atom of magnesium is involved to shield the negative charges on the phosphate groups of the ATP molecule.

Step 8: Phosphoglycerate Mutase

The enzyme phosphoglycero mutase relocates the P from 3- phosphoglycerate from the 3rd carbon to the 2nd carbon to form 2-phosphoglycerate.

This step involves a simple rearrangement of the position of the phosphate group on the 3 phosphoglycerate molecule, making it 2 phosphoglycerate. The molecule responsible for catalyzing this reaction is called phosphoglycerate mutase (PGM). A mutase is an enzyme that catalyzes the transfer of a functional group from one position on a molecule to another.

The reaction mechanism proceeds by first adding an additional phosphate group to the 2′ position of the 3 phosphoglycerate. The enzyme then removes the phosphate from the 3′ position leaving just the 2′ phosphate, and thus yielding 2 phsophoglycerate. In this way, the enzyme is also restored to its original, phosphorylated state.

Step 9: Enolase

The enzyme enolase removes a molecule of water from 2-phosphoglycerate to form phosphoenolpyruvic acid (PEP).

This step involves the conversion of 2 phosphoglycerate to phosphoenolpyruvate (PEP). The reaction is catalyzed by the enzyme enolase. Enolase works by removing a water group, or dehydrating the 2 phosphoglycerate. The specificity of the enzyme pocket allows for the reaction to occur through a series of steps too complicated to cover here.

Step 10: Pyruvate Kinase

The enzyme pyruvate kinase transfers a P from phosphoenolpyruvate (PEP) to ADP to form pyruvic acid and ATP Result in step 10.

The final step of glycolysis converts phosphoenolpyruvate into pyruvate with the help of the enzyme pyruvate kinase. As the enzyme’s name suggests, this reaction involves the transfer of a phosphate group. The phosphate group attached to the 2′ carbon of the PEP is transferred to a molecule of ADP, yielding ATP. Again, since there are two molecules of PEP, here we actually generate 2 ATP molecules.

Steps 1 and 3 = – 2ATP Steps 7 and 10 = + 4 ATP Net “visible” ATP produced = 2.

Immediately upon finishing glycolysis, the cell must continue respiration in either an aerobic or anaerobic direction; this choice is made based on the circumstances of the particular cell. A cell that can perform aerobic respiration and which finds itself in the presence of oxygen will continue on to the aerobic citric acid cycle in the mitochondria. If a cell able to perform aerobic respiration is in a situation where there is no oxygen (such as muscles under extreme exertion), it will move into a type of anaerobic respiration called homolactic fermentation. Some cells such as yeast are unable to carry out aerobic respiration and will automatically move into a type of anaerobic respiration called alcoholic fermentation.

Similar Posts:

  • Krebs (Citric Acid) Cycle Steps by Steps Explanation
  • Pyruvate Broth Test – Principle, Procedure, Uses and Interpretation
  • Antibiotics: Comprehensive Guide
  • PYR Test- Principle, Uses, Procedure and Result Interpretation

84 thoughts on “Glycolysis Explained in 10 Easy Steps”

Thanks for describing this in detail. I am wondering though, glycolysis described here may thought to be for human metabolism, but I am not sure if this is the only pathway for glycolysis in humans. I am a believer in exogenous enzyme helping human (and mammalian) metabolism, by means of acquiring it gastronomically. Modern human food does not include metabolic enzymes in general. but it does not mean it is not possible for exogenous enzyme to work in the body, nor it is unhealthy to acquire one. Are those enzymes you described the only enzymes coded in human DNA?

Thanks for the explanation sir. It was a very good one. I tried to understand it during my biochemistry class but was difficult, but with this, it’s going to be easy for me to understand

please someone tell me which are phosphorylated steps and splitting steps ? indicating by step number.

step 7 and 10 produce atp thru subtrate level phosphyrlation

Is pyruvate produced through a process of glycolysis?

Yes it’s produce at the end in an aerobic condition

How many ATP produced when fructose or glucose enters the glycolysis pathway

Number of total atp produced is 2

a net of two ATPs is produced

Net ATPs produced are 2 but 2 NADH are also produced which in Electron Transport Chain each produces 3 ATPs so according to this idea 3×2=6 ATPs and overall ATPs produced are 2+6=8 ATPs.

2 ATP molecules are produced for every molecules of glucose that goes into glycolysis

4, ATP but, again 2atp were used in the process so our net gain is:2 ATP

10 steps in glycolysis, how many of them consume ATP?

ATP Consumed in step one and three respectively

2 steps consume ATP ie the phosphorylation step that occurs at first, the other phosphorylation step that occurs after isomerism

what happens to the hydrogens in step 1 and step 3 ?

This is for everyone asking about this. Usually all the remaining products can be used for a new source a energy.

Remember Energy can niether be created nor distroyed Study the mechanism critically They are only being converted to a different form

Actually they have been converted to other forms, I could not understand the whole process but the char has made it simplest

Forms water or is used up for other source of energy

They are converted to water

Your question: “what happens to the hydrogens in step 1 and step 3 ?”

1) In reaction 1, glucose gets phosphorylated (i.e addition of phosphate group) at its 6th carbon atom (i.e the CH2OH molecule), so, the bond formation between the phosphate group and the CH2OH leads to the ‘removal of the H atom of the OH (hydroxyl) group’ from the CH2OH molecule. The 6th carbon atom of glucose looks like this ‘C+H+H+OH’ i.e C has H+H+OH attached to it. So, phosphate comes in, removes the H of the OH, and attaches to the remaining ‘O’ of the OH. That’s why reaction 1 has Glucose-6-Phosphate + ADP + ‘H’.

2) For reaction 3, it’s the same process (as reaction 1) by which another phosphate group is added to fructose-6-phosphate, but this time on its 1st carbon atom, phosphate goes in and removes the H of the OH on the CH2OH on carbon 1 of fructose, attaches itself to carbon 1, thus release another H atom.

Although the ADP is the result of hydrolysis of ATP i.e when you remove just one phosphate group from ATP (Adenosine Triphosphate: Adenosine with three phosphate groups), you get ADP (Adenosine Diphosphate: Adenosine with two phosphate groups).

lost 1 H+ for each step

Glucose is phosphorylated in the first step because you want the glucose to be trapped in the cell to continue in the pathway. Without this, the glucose will be sent out of the cell via transporters. This also initiates the reduction of instability of the glucose to increase its reactivity.

“This also initiates the reduction of instability of the glucose to increase its reactivity.” I thought the point was to increase the instability of glucose, by adding the second phosphate to the other side to make fructose 1, 6 bisphosphate. Now the two phosphates push away from each other and make it easy work for aldolase to split the molecule in two.

Thanks a lots. But how do we do the calculation under this?

Thanks but I have a question that why glucose is phosphorylated in the first step of glycolysis

to realise one Phosphate from ATP, then ATP(adenosin triphosphate) turns into ADP(adenosin diphosphate), the phospate realised will be added to glucose, then glucose turns into glucose 6 Phosphate.

To capture glucose in the cell first it phosphorylated then the next process is proceed

Well, this occurs due to the fact that phosphorylation can keep a molecule from diffusing out of its position; making it more reactive by borrowing a phosphate molecule from ATP. Adenosine Triphosphate (3 phosphate) Which is converted to ADP (Adenosine Diphosphate) GLUCOSE- GLUCOSE 6 PHOSPHATE

Why not other compound used to make glucose become active, but only phosphate group is used?

In the last reaction PEPA +ADP…. from where ADP com from

It gets attached to 6th carbon as it’s easily accessible than other carbons and needs less energy

It also happens to keep the glucose in the cell insted of losing it out

In g3p dehydrogenase. . How oxygen is attached to po3 from where it come.. N how h+ is formed the released H is involved to form and to nadh

Actually G3P is first converted to 1-3- bi phosphogleraldehyde with the help of H3PO4 & H20. It is a non enzymatic reaction. 1-3- bi phosphogleraldehyde is then converted to 1-3 bi phosphogleceric acid. Here NAD is reduced to NADH. But for this conversion 1/2 O2 is required, because NADH must be oxidized to form NAD, ( NAD is electron carrier) without which this conversion will not take place ( enzyme required is G-3 phosphate Dehydrogenase). Therefore 1) for oxidation of Nadh 2) High energy of electron is then produce ATP, and as a terminal acceptor of electron, O2 is required. ( 1/2 O2 x 2 cycle = 1 mol of O2 required). Hope this is clear.

But what is the electron here,is it H- and if it is then how H- is produced???

thanks alot but i have a question, why is it that normally during phosphorylation ATP is consumed but during glyceraldehyde phosphate dehydrogenase when the inorganic phosphate was added to the molecule, ATP was not consumed why??

Because there are free floating inorganic phosphates in the cytosol of the cell that are used for the phosphorylation of that substrate where ATP is not required.

Because dehygenase enzyme requires NAD as a cofactor

this is exactly what my teacher has taught in the classroom. reading this seems as if i am reading his own written steps of the glycolysis process. Thank you very much.

This is a great survey of glycolysis. Our class does go in more depth, but I can’t think of a better resource to start with. Thanks so much! I shared it with all my classmates. I hope your page gets sore from all the web hits it is gonna get!

Each NADH will produce approx 2.5 ATP during the election transport chain.

Thanks I appreciate this impressive literature ,quite educative we need more of this concerning glycogen

Please i want to understand how the net yield of 8ATPs in aerobic glycolysis is realized. Thank you

Thank God I came across this.. Best one I’ve read on Glycolysis so far.. Even better than my textbooks..

Were do the other hydrogens goes after the splitting of fructose in step 4?

when one AtP molecules is produce and other one is consumed so what effect on glycolysis???

It will result to low yield at the end of the process

In the last step where phosphoenol pyruvate is converted to pyruvic acid! Where is the Hydrogen atom coming from?

why is there a H atom again on the 2 CARBON in the 10 step when we removed it as H2O in the 9th step.

Thank you very much, I thought triose phosphate was the main intermediate which continues glycolysis. Thanks fr clearing this dilemma

I’ve searched and searched for the easiest to understand discussion about Glycolysis and I was not disappointed by the way you presented the complexity of the process. (Honestly, I can feel how you really want to let the readers understand the concepts in a friendly language to help them keep up with every step.) Thanks a lot!

Honestly this is amazing. l couldn’t get it right in class ,but I understand it now. Thanks alot

Dear sir the chemical formula of phosphoenole pyruvate is c3h5o6p and you write c3h4o3p.

Pls help me and explain how fruit you just taken will enter into glycolytic pathway.

most of the fruits you eat will breakdown as simpler substances so that cell can consume it. in further processes glucose will be converted to pyruvate.In simple words most of the food items contains glucose or its combined forms like sucrose .etc.when you eat an apple you are taking in glucose .glycolytic cycle occurs in cell organelles like mitochondria .etc.these all happens the very moment when something reaches your stomach.

dear thanks for making it easy. pls can you simplify electron transport chain/ oxidative phosphorylation.

I don’t actually knows how to express to you my thanks, because the way you splits, disintegrates, and break down this glycolic pathway I’m so impressed. To be honest before I found this, I suffered a lot on how to understand this thing.Because I didn’t attends the lectures at school when the lecturer is conducting it. But now I’m fully convinced and fully understand it. Thank You so much. {I wish that, all your wishes be granted}

Do you have the same excelently written Krebs Cycle as you have done in the glycolisis cycle ?. You have done an outstanding job.

Well written notes.Please mark on structure how the six carbon breaks into 3carbons compounds in step 4

For anyone who is still confused on step 6 watch https://www.youtube.com/watch?v=_sXCPL241Hk 0:00 – 4:47

Kindly give an explanation behind the negative 2 ATP molecules in the first and third steps

Kindly describe the process in the mitochondria as well. Also please do the same for gluconeogenesis, glycogenesis and glucogenolysis.

I like the way all the steps have been outlined for easy understanding. I found this very helpful. With some level of effort, I now have all the 10 steps on my finger tips for my biochemistry class. Thank you so much for sharing.

I have a doubt,from where does the phosphate in step 6 come from? It just says that phosphate is added. Anyway the answer was useful,Thank you!

it would have been much better if the energy released or absorbed at each stage was included.

I don’t understand the role of magnesium, can you explain it more clearly?

The role is clear that it shields the highly reactive negative charge phosphate from reacting with ADP molecules but how does the cofactor and enzyme distinguish between ADP and ATP when both have a difference of one phosphate group.

Unexplained: H2O removal from Phosphoglycerate should leave PEP and Pyruvate with 2 H. But Pyruvate has 4 H. Does 2H reenter PEP

Good discussion , I was enlightened by the specifics , Does anyone know if I could acquire a blank WI WB-42 example to use ?

For each molecule of glucose two molecules of payruvic acid (payruvate) formed…

Am happy to get this note thanks sir Ghana Kumasi polytechnic please I want to know this since there were two molecules of PEP,was two molecules of pyruvate compound formed?

yeah, two molecules of pyruvate are formed and they all jump into citric acid cycle(kreb cycle) with the help of pyruvate dehydrogenase.

now this is the best thing i have read so far on glycolysis.even my text book can’t explain it well.thank you very much.

This is easier than the ones I’ve encountered and makes my work a lot more easy I need this for my write up and I need to explain it as well for my final year paper as an Animal Nutritionist thanks a lot DR

Archea can srvive in harsh environmenatl conditions because of its specific Cell wall and cell membrane compositions.

Thanx for the illustration. I have a query regarding structure of glucose. You have placed hydroxyl group in structure of glucose down in first carbon. Same is the case in second carbon, but you have placed hydroxyl group in third carbon up. Does it have to be so specific? I mean, cant we place hydroxyl group in first carbon up or hydroxyl group in third carbon down? I have save same question regarding placement of hydroxyl group in 3 carbon structures ie left or right.

In aerobic glucose metabolism, the oxidation of citric acid uses ADP and Mg²+, which will increase the speed of reaction: Iso-citric acid + NADP (NAD) — isocitrate dehydrogenase (IDH) = alpha-ketoglutaric acid. In the Krebs cycle (the citric cycle), IDH1 and IDH2 are NADP+-dependent enzymes that normally catalyze the inter-conversion of D-isocitrate and alpha-ketoglutarate (α-KG). The DH1 and IDH2 genes are mutated in > 75% of different malignant diseases. Two distinct alterations are caused by tumor-derived mutations in IDH1 or IDH2: loss of its normal catalytic activity during the production of α-ketoglutarate (α-KG) and the gain of catalytic activity to produce 2-hydroxygulatrate (2-HG). This product is a competitive inhibitor of multiple α-KG-dependent dioxygenases, including histone, demethylases, prolyl-4-hydroxylase and the TET enzymes family (Ten-Eleven Translocation-2), resulting in genome-wide alternations in histones and DNA methylation. IDH1 and IDH2 mutations have been observed in myeloid malignancies, including de novo and secondary AML (15%–30%), and pre-leukemic clone malignancies, including myelodysplastic syndrome and myeloproliferative neoplasms (85% of the chronic phase and 20% of transformed cases in acute leukemia). The energetic sum of anaerobic glycolysis is ΔGo = -34.64 kcal/mol. However, a glucose molecule contains 686 kcal/mol and the energy difference (654.51 kcal) remains a potential for un-controlled reactions in carcinogenesis. The transfer of electrons from NADPH in each place of the conserved unit of energy transmits conformational exchanges of mitochondrial ATPases. In the reaction, ADP³+ P²¯ + H²– ATP + H2O it is a reversible reaction. The terminal oxygen from ADP binds the atom P2¯ by forming an intermediate pentacovalent length and synthesizing the molecular complexes ATP and H2O. This reaction requires Mg²+ and ATP-synthetase, which is known as the H+-ATPase or the Fo-F1-ATPase complex, where FO is a conductor proton and F1 is synthesized. Mg2+ stabilizes the mitochondrial membrane via the high electronegativity of its electrons. In contrast, intracellular calcium induces mitochondrial swelling and aging. Mg2+ generally interacts with substrates via the inner coordination sphere, stabilizing anions or reactive intermediates, binding ATP and activating the molecule for nucleophilic attack.

I’m glad to see this post, as a student of nutrition for better health and aging. How does this relate to Diabetes? Can you connect the dot for the general public? I’ve read dozens of books on diet and nutrition, but only getting confused, without conceptual biological-chemical bases to validate many contradictory claims.

I am glad to see that you included the delta-G values in the principal figure. These are very important for helping students appreciate how the flow operates in these pathways, but the values are often left out of figures for the sake of simplicity. At the same time, I would recommend adding arrows for the reverse reactions, perhaps with length indicating the free energy vector, to further emphasize and distinguish the freely reversible from essentially irreversible reactions. It might also help to add both the free energy values and the reverse arrows to the single-step figures, as well. Overall, this is a pretty good study review.

Nice theory

Leave a Comment Cancel reply

Save my name and email in this browser for the next time I comment.

Glycolysis: The First Stage in Cellular Respiration

Thomas Shafee / CC BY 4.0 / Wikimedia Commons

  • Cell Biology
  • Weather & Climate
  • B.A., Biology, Emory University
  • A.S., Nursing, Chattahoochee Technical College

Glycolysis, which translates to "splitting sugars", is the process of releasing energy within sugars. In glycolysis, a six-carbon sugar known as glucose is split into two molecules of a three-carbon sugar called pyruvate. This multistep process yields two ATP molecules containing free energy , two pyruvate molecules, two high energy, electron-carrying molecules of NADH, and two molecules of water.

  • Glycolysis is the process of breaking down glucose.
  • Glycolysis can take place with or without oxygen.
  • Glycolysis produces two molecules of pyruvate , two molecules of ATP , two molecules of NADH , and two molecules of water .
  • Glycolysis takes place in the cytoplasm .
  • There are 10 enzymes involved in breaking down sugar. The 10 steps of glycolysis are organized by the order in which specific enzymes act upon the system.

Glycolysis can occur with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration . In the absence of oxygen, glycolysis allows cells to make small amounts of ATP through a process of fermentation.

Glycolysis takes place in the cytosol of the cell's cytoplasm . A net of two ATP molecules are produced through glycolysis (two are used during the process and four are produced.) Learn more about the 10 steps of glycolysis below.

The enzyme hexokinase phosphorylates or adds a phosphate group to glucose in a cell's cytoplasm . In the process, a phosphate group from ATP is transferred to glucose producing glucose 6-phosphate or G6P. One molecule of ATP is consumed during this phase.

The enzyme phosphoglucomutase isomerizes G6P into its isomer fructose 6-phosphate or F6P. Isomers have the same molecular formula as each other but different atomic arrangements.

The kinase phosphofructokinase uses another ATP molecule to transfer a phosphate group to F6P in order to form fructose 1,6-bisphosphate or FBP. Two ATP molecules have been used so far.

The enzyme aldolase splits fructose 1,6-bisphosphate into a ketone and an aldehyde molecule. These sugars, dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP), are isomers of each other.

The enzyme triose-phosphate isomerase rapidly converts DHAP into GAP (these isomers can inter-convert). GAP is the substrate needed for the next step of glycolysis.

The enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH) serves two functions in this reaction. First, it dehydrogenates GAP by transferring one of its hydrogen (H⁺) molecules to the oxidizing agent nicotinamide adenine dinucleotide (NAD⁺) to form NADH + H⁺.

Next, GAPDH adds a phosphate from the cytosol to the oxidized GAP to form 1,3-bisphosphoglycerate (BPG). Both molecules of GAP produced in the previous step undergo this process of dehydrogenation and phosphorylation.

The enzyme phosphoglycerokinase transfers a phosphate from BPG to a molecule of ADP to form ATP. This happens to each molecule of BPG. This reaction yields two 3-phosphoglycerate (3 PGA) molecules and two ATP molecules.

The enzyme phosphoglyceromutase relocates the P of the two 3 PGA molecules from the third to the second carbon to form two 2-phosphoglycerate (2 PGA) molecules.

The enzyme enolase removes a molecule of water from 2-phosphoglycerate to form phosphoenolpyruvate (PEP). This happens for each molecule of 2 PGA from Step 8.

The enzyme pyruvate kinase transfers a P from PEP to ADP to form pyruvate and ATP. This happens for each molecule of PEP. This reaction yields two molecules of pyruvate and two ATP molecules.

  • An Introduction to Types of Respiration
  • All About Cellular Respiration
  • Citric Acid Cycle Steps
  • Calvin Cycle Steps and Diagram
  • The Difference Between Fermentation and Anaerobic Respiration
  • The Photosynthesis Formula: Turning Sunlight into Energy
  • What You Need To Know About Adenosine Triphosphate or ATP
  • Electron Transport Chain and Energy Production Explained
  • Mitochondria: Power Producers
  • Photosynthesis Basics - Study Guide
  • Photosynthesis Vocabulary Terms and Definitions
  • The 5 Kinds of Nucleotides
  • 10 Great Biology Activities and Lessons
  • Why Is the Krebs Cycle Called a Cycle?
  • Aerobic vs. Anaerobic Processes
  • Citric Acid Cycle or Krebs Cycle Overview

Logo for Open Oregon Educational Resources

Aerobic Respiration, Part 1: Glycolysis

You have read that nearly all of the energy used by living things comes to them in the bonds of the sugar, glucose. Glycolysis is the first step in the breakdown of glucose to extract energy for cell metabolism. Many living organisms carry out glycolysis as part of their metabolism. Glycolysis takes place in the cytoplasm of most prokaryotic and all eukaryotic cells.

Glycolysis begins with a molecule of glucose (C 6 H 12 O 6 ). Various enzymes are used to break glucose down into two molecules of pyruvate (C 3 H 4 O 3 , basically a glucose molecule broken in half) ( Figure 1 ). This process releases a small amount of energy.

write a essay on glycolysis

Glycolysis consists of two distinct phases: energy-requiring, and energy-producing.

Energy-Requiring Steps

The first part of the glycolysis pathway requires an input of energy to begin. The first step in glycolysis is catalyzed by hexokinase, an enzyme with broad specificity that catalyzes the phosphorylation of six-carbon sugars. Hexokinase phosphorylates (adds a phosphate to) glucose using ATP as the source of the phosphate ( Figure 2 ). This produces glucose-6-phosphate, a more chemically reactive form of glucose. This phosphorylated glucose molecule can no longer leave the cell because the negatively charged phosphate will not allow it to cross the hydrophobic interior of the plasma membrane.

Several additional enzymatic reactions occur ( Figure 2 ), one of which requires an additional ATP molecule. At the end of the energy-requiring steps, the original glucose has been split into two three-carbon molecules, and two ATPs have been used as sources of energy for this process.

shows chemical structures of molecules in the first half of glycolysis.

Energy-Producing Steps

So far, glycolysis has cost the cell two ATP molecules and produced two small, three-carbon sugar molecules. Both of these molecules will proceed through the second half of the pathway, and sufficient energy will be extracted to pay back the two ATP molecules used as an initial investment and produce a profit for the cell of two additional ATP molecules and two even higher-energy NADH molecules ( Figure   3 ).

During the energy-producing steps, additional enzymes continue to catalyze the breakdown of glucose ( Figure 3 ). The end result of these reactions is two 3-carbon molecules of pyruvate.

more chemical reactions in glycolysis

An important rate-limiting step occurs at step 6 in glycolysis. If you look at Figure 3, you will notice that during step 6, NAD + is converted into NADH.  NADH contains more energy than NAD + , and is therefore a desired product from this reaction. However, the continuation of the reaction depends upon the availability NAD + . Thus, NADH must be continuously converted back into NAD + in order to keep this step going. If NAD + is not available, the second half of glycolysis slows down or stops.

If oxygen is available in the system, the NADH will be converted readily back into NAD + by the later processes in aerobic cellular respiration. However, if there is no oxygen available, NADH is not converted back into NAD + . Without NAD + , the reaction in step 6 cannot proceed and glycolysis slows or stops. In an environment without oxygen, an alternate pathway (fermentation) can provide the oxidation of NADH to NAD + .

Outcomes of Glycolysis

Glycolysis starts with glucose and ends with two pyruvate molecules, a total of four ATP molecules and two molecules of NADH. Two ATP molecules were used in the first half of the pathway to prepare the six-carbon ring for cleavage, so the cell has a net gain of two ATP molecules and 2 NADH molecules for its use. If the cell cannot catabolize (break down) the pyruvate molecules further, it will harvest only two ATP molecules from one molecule of glucose. Mature mammalian red blood cells are not capable of aerobic respiration—the process in which organisms convert energy in the presence of oxygen—and glycolysis is their sole source of ATP. If glycolysis is interrupted, these cells lose their ability to maintain their sodium-potassium pumps, and eventually, they die.

Section Summary

Glycolysis is the first pathway used in the breakdown of glucose to extract energy. It was probably one of the earliest metabolic pathways to evolve and is used by nearly all of the organisms on earth. Glycolysis consists of two parts: The first part prepares the six-carbon ring of glucose for cleavage into two three-carbon sugars. ATP is invested in the process during this half to energize the separation. The second half of glycolysis extracts ATP and high-energy electrons from hydrogen atoms and attaches them to NAD + . Two ATP molecules are invested in the first half and four ATP molecules are formed by substrate phosphorylation during the second half. This produces a net gain of two ATP and two NADH molecules for the cell.

What was produced (per molecule of glucose)?

  • 2 pyruvate (3 carbon molecules), 2 NADH, net gain of 2 ATP

Unless otherwise noted, images on this page are licensed under CC-BY 4.0  by  OpenStax .

OpenStax , Concepts of Biology. OpenStax CNX. May 18, 2016 http://cnx.org/contents/[email protected]

OpenStax , Biology. OpenStax CNX. September 16, 2017 https://cnx.org/contents/[email protected]:tYtpI6rX@6/Glycolysis

Principles of Biology Copyright © 2017 by Lisa Bartee, Walter Shriner, and Catherine Creech is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

Share This Book

  • Biology Article
  • Glycolysis Glycolytic Pathway

Glycolysis: An Introduction To Glycolytic Pathway

Glycolysis

All living organisms undergo respiration. Although there are a wide variety of organisms, the biochemical reactions that constitute respiration are very similar in all organisms, starting from bacteria all the way to human beings. So what is glycolysis? It is the first step of respiration in all organisms.

Pathway of Glycolysis

Like all biochemical reactions, glycolysis follows a pathway, i.e., a series of chemical reactions each of which is catalyzed by a separate enzyme.

Pathway of Glycolysis

Glycolytic pathway is the first step in respiration, where glucose, the respiratory substrate, is oxidized to a simpler organic compound. This is an exergonic reaction, i.e., energy is released, which is used to produce ATP from ADP. ATP can then be used to drive life processes which require energy.

Where does glycolysis take place?

The reactions of the Glycolytic pathway takes place in the cytosol.

Key events in glycolysis

The initial requirement of atp.

ATP is required for the hydrolysis of ATP to ADP. In this reaction, energy is required in the same way:

For instance- A businessman has to invest money first to buy some goods so that he can then sell them at a higher price to make some profit.

Similarly, the cell first spends some ATP molecules, but later gets back more ATP molecules, so there is a net gain of ATP molecules. As mentioned in the above image, 1 molecule of ATP is used to make glucose-6-phosphate from glucose and fructose-1,6-bisphosphate from fructose-6-phosphate.

The overall process of glycolysis is an oxidation reaction. In this reaction, glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate, which involves the oxidation of an aldehyde group to a carboxylic acid group. The electrons that are lost by glyceraldehyde-3-phosphate are taken up by NAD + , which gets reduced to NADH. The extra phosphate group of 1,3-bisphosphoglycerate comes from Pi (inorganic phosphate), which is nothing but a phosphate ion.

ATP formation

Finally, we come to the most exciting part. How does the cell produce high energy ATP molecules?

1,3-Bisphosphate-glycerate to 3-phosphoglycerate: Since the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate is an oxidation reaction, it is exergonic. The energy released makes the phosphate linkage in carbon 1 of 1,3-bisphosphoglycerate a very high energy bond. This bond is next broken to release a lot of energy, which is then used to make an ATP molecule from an ADP molecule.

Phosphoenolpyruvate to pyruvate: This is the last step of glycolysis. The phosphate linkage in phosphoenolpyruvate has very high bond energy. This is broken to make ATP.

The fate of NADH

What happens to the NADH produced in the Glycolytic pathway? It has to be re-oxidized to NAD + so that the Glycolytic pathway can continue to take place. It depends on whether the respiration is anaerobic or aerobic.

Anaerobic respiration: This occurs in the absence of oxygen.

  • Production of lactic acid: The NADH, in order to get converted back to NAD + , gives its electrons to pyruvate, the end product of glycolysis. Pyruvate, in turn, gets reduced to lactate or lactic acid. This is what happens in curd formation by bacteria and in our muscles when we do some strenuous work.
  • Production of ethanol: Pyruvate can also lose carbon to form acetaldehyde, which then accepts electrons from NADH to form ethanol. This is what happens in yeast and during anaerobic respiration in plants.

Aerobic respiration: In the presence of oxygen, NADH donates its electrons to oxygen through the electron transport chain in the mitochondrial inner membrane.

How many ATP molecules are produced by the Glycolytic pathway?

Substrate level phosphorylation: 2 ATP molecules per glucose molecule are invested initially in the glycolytic pathway. Later on, as mentioned above, two steps produce one ATP molecule each. However, from each glucose molecule, 2 molecules each of 1,3-bisphosphoglycerate and phosphoenolpyruvate are used. Hence, per glucose molecule, 4 ATP molecules are produced. ATP produced this way is called substrate-level phosphorylation.

Oxidative phosphorylation: When an NADH molecule gives its electrons to oxygen through the electron transport chain in mitochondria, 3 ATP molecules are produced. Since 2 NADH molecules are produced per glucose molecules, a total of 6 ATP molecules are produced by oxidative phosphorylation.

This was an introduction to glycolysis. For more information about glycolysis, visit BYJU’S.

Quiz Image

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

Visit BYJU’S for all Biology related queries and study materials

Your result is as below

Request OTP on Voice Call

Leave a Comment Cancel reply

Your Mobile number and Email id will not be published. Required fields are marked *

Post My Comment

write a essay on glycolysis

  • Share Share

Register with BYJU'S & Download Free PDFs

Register with byju's & watch live videos.

close

If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

To log in and use all the features of Khan Academy, please enable JavaScript in your browser.

Biology library

Course: biology library   >   unit 12, overview of glycolysis.

  • Steps of glycolysis

Want to join the conversation?

  • Upvote Button navigates to signup page
  • Downvote Button navigates to signup page
  • Flag Button navigates to signup page

Incredible Answer

Video transcript

Library homepage

  • school Campus Bookshelves
  • menu_book Bookshelves
  • perm_media Learning Objects
  • login Login
  • how_to_reg Request Instructor Account
  • hub Instructor Commons
  • Download Page (PDF)
  • Download Full Book (PDF)
  • Periodic Table
  • Physics Constants
  • Scientific Calculator
  • Reference & Cite
  • Tools expand_more
  • Readability

selected template will load here

This action is not available.

Biology LibreTexts

9.3: Glycolysis

  • Last updated
  • Save as PDF
  • Page ID 103590

Learning Objectives

By the end of this section, you will be able to do the following:

  • Describe the overall result in terms of molecules produced during the chemical breakdown of glucose by glycolysis
  • Compare the output of glycolysis in terms of ATP molecules and NADH molecules produced

As you have read, nearly all of the energy used by living cells comes to them in the bonds of the sugar glucose. Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. In fact, nearly all living organisms carry out glycolysis as part of their metabolism. The process does not use oxygen directly and therefore is termed anaerobic . Glycolysis takes place in the cytoplasm of both prokaryotic and eukaryotic cells. Glucose enters heterotrophic cells in two ways. One method is through secondary active transport in which the transport takes place against the glucose concentration gradient. The other mechanism uses a group of integral proteins called GLUT proteins , also known as glucose transporter proteins. These transporters assist in the facilitated diffusion of glucose.

Glycolysis begins with the six-carbon ring-shaped structure of a single glucose molecule and ends with two molecules of a three-carbon sugar called pyruvate . Glycolysis consists of two distinct phases. The first part of the glycolysis pathway traps the glucose molecule in the cell and uses energy to modify it so that the six-carbon sugar molecule can be split evenly into the two three-carbon molecules. The second part of glycolysis extracts energy from the molecules and stores it in the form of ATP and NADH—remember: this is the reduced form of NAD.

The illustration shows a simplified process of glucose moving through the stages of glycolysis. First two A T P are added, then the glucose is split into two branches, with N A D H and two A T P being released.  The net products are 2 pyruvate molecules and 2 N A D H and 2 A T P molecules.

First Half of Glycolysis (Energy-Requiring Steps)

Step 1 . The first step in glycolysis (Figure 7.8) is catalyzed by hexokinase, an enzyme with broad specificity that catalyzes the phosphorylation of six-carbon sugars. Hexokinase phosphorylates glucose using ATP as the source of the phosphate, producing glucose-6-phosphate, a more reactive form of glucose. This reaction prevents the phosphorylated glucose molecule from continuing to interact with the GLUT proteins, and it can no longer leave the cell because the negatively charged phosphate will not allow it to cross the hydrophobic interior of the plasma membrane.

Step 2 . In the second step of glycolysis, an isomerase converts glucose-6-phosphate into one of its isomers, fructose-6-phosphate (this isomer has a phosphate attached at the location of the sixth carbon of the ring). An isomerase is an enzyme that catalyzes the conversion of a molecule into one of its isomers. (This change from phosphoglucose to phosphofructose allows the eventual split of the sugar into two three-carbon molecules.)

Step 3 . The third step is the phosphorylation of fructose-6-phosphate, catalyzed by the enzyme phosphofructokinase. A second ATP molecule donates a high-energy phosphate to fructose-6-phosphate, producing fructose-1,6- bi sphosphate. In this pathway, phosphofructokinase is a rate-limiting enzyme. It is active when the concentration of ADP is high; it is less active when ADP levels are low and the concentration of ATP is high. Thus, if there is “sufficient” ATP in the system, the pathway slows down. This is a type of end product inhibition, since ATP is the end product of glucose catabolism.

Step 4 . The newly added high-energy phosphates further destabilize fructose-1,6-bisphosphate. The fourth step in glycolysis employs an enzyme, aldolase, to cleave fructose-1,6-bisphosphate into two three-carbon isomers: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.

Step 5 . In the fifth step, an isomerase transforms the dihydroxyacetone-phosphate into its isomer, glyceraldehyde-3-phosphate. Thus, the pathway will continue with two molecules of a glyceraldehyde-3-phosphate. At this point in the pathway, there is a net investment of energy from two ATP molecules in the breakdown of one glucose molecule.

This illustration shows the steps in the first half of glycolysis. In step one, the enzyme hexokinase uses one A T P molecule in the phosphorylation of glucose. In step two, glucose dash 6 dash phosphate is rearranged to form fructose dash 6  dash phosphate by phosphoglucose isomerase. In step three, phosphofructokinase uses a second A T P molecule in the phosphorylation of the substrate, forming fructose dash 1, 6 dash bisphosphate. The enzyme fructose bisphosphate aldose splits the substrate into two, forming glyceraldeyde dash 3 dash phosphate and dihydroxyacetone-phosphate. In step 4, triose phosphate isomerase converts the dihydroxyacetone-phosphate into glyceraldehyde dash 3 dash phosphate.

Second Half of Glycolysis (Energy-Releasing Steps)

So far, glycolysis has cost the cell two ATP molecules and produced two small, three-carbon sugar molecules. Both of these molecules will proceed through the second half of the pathway, and sufficient energy will be extracted to pay back the two ATP molecules used as an initial investment and produce a profit for the cell of two additional ATP molecules and two even higher-energy NADH molecules.

Step 6 . The sixth step in glycolysis (Figure 7.9) oxidizes the sugar (glyceraldehyde-3-phosphate), extracting high-energy electrons, which are picked up by the electron carrier NAD + , producing NADH. The sugar is then phosphorylated by the addition of a second phosphate group, producing 1,3-bisphosphoglycerate. Note that the second phosphate group does not require another ATP molecule.

This illustration shows the steps in the second half of glycolysis. In step six, the enzyme glyceraldehydes dash 3 dash phosphate dehydrogenase produces one N A D H molecule and forms 1 3 dash bisphosphoglycerate. In step seven, the enzyme phosphoglycerate kinase removes a phosphate group from the substrate, forming one A T P molecule and 3 dash phosphoglycerate. In step eight, the enzyme phosphoglycerate mutase rearranges the substrate to form 2 dash phosphoglycerate. In step nine, the enzyme enolase rearranges the substrate to form phosphoenolpyruvate. In step ten, a phosphate group is removed from the substrate, forming one A T P molecule and pyruvate.

Here again is a potential limiting factor for this pathway. The continuation of the reaction depends upon the availability of the oxidized form of the electron carrier, NAD + . Thus, NADH must be continuously oxidized back into NAD + in order to keep this step going. If NAD + is not available, the second half of glycolysis slows down or stops. If oxygen is available in the system, the NADH will be oxidized readily, though indirectly, and the high-energy electrons from the hydrogen released in this process will be used to produce ATP. In an environment without oxygen, an alternate pathway (fermentation) can provide the oxidation of NADH to NAD + .

Step 7 . In the seventh step, catalyzed by phosphoglycerate kinase (an enzyme named for the reverse reaction), 1,3-bisphosphoglycerate donates a high-energy phosphate to ADP, forming one molecule of ATP. (This is an example of substrate-level phosphorylation.) A carbonyl group on the 1,3-bisphosphoglycerate is oxidized to a carboxyl group, and 3-phosphoglycerate is formed.

Step 8 . In the eighth step, the remaining phosphate group in 3-phosphoglycerate moves from the third carbon to the second carbon, producing 2-phosphoglycerate (an isomer of 3-phosphoglycerate). The enzyme catalyzing this step is a mutase (isomerase).

Step 9 . Enolase catalyzes the ninth step. This enzyme causes 2-phosphoglycerate to lose water from its structure; this is a dehydration reaction, resulting in the formation of a double bond that increases the potential energy in the remaining phosphate bond and produces phosphoenolpyruvate (PEP).

Step 10 . The last step in glycolysis is catalyzed by the enzyme pyruvate kinase (the enzyme in this case is named for the reverse reaction of pyruvate’s conversion into PEP) and results in the production of a second ATP molecule by substrate-level phosphorylation and the compound pyruvic acid (or its salt form, pyruvate). Many enzymes in enzymatic pathways are named for the reverse reactions, since the enzyme can catalyze both forward and reverse reactions (these may have been described initially by the reverse reaction that takes place in vitro, under nonphysiological conditions).

Link to Learning

Gain a better understanding of the breakdown of glucose by glycolysis by visiting this site to see the process in action.

Outcomes of Glycolysis

Glycolysis begins with glucose and produces two pyruvate molecules, four new ATP molecules, and two molecules of NADH. (Note: two ATP molecules are used in the first half of the pathway to prepare the six-carbon ring for cleavage, so the cell has a net gain of two ATP molecules and two NADH molecules for its use). If the cell cannot catabolize the pyruvate molecules further, it will harvest only two ATP molecules from one molecule of glucose. Mature mammalian red blood cells do not have mitochondria and thus are not capable of aerobic respiration —the process in which organisms convert energy in the presence of oxygen—and glycolysis is their sole source of ATP. If glycolysis is interrupted, these cells lose their ability to maintain their sodium-potassium pumps, and eventually, they die.

The last step in glycolysis will not occur if pyruvate kinase, the enzyme that catalyzes the formation of pyruvate, is not available in sufficient quantities. In this situation, the entire glycolysis pathway will proceed, but only two ATP molecules will be made in the second half. Thus, pyruvate kinase is a rate-limiting enzyme for glycolysis.

Glycolysis Process and Its Stages

Glycolysis is a specific process that is known as the first stage of the anaerobic respiration process in plants, during which 6-carbon glucose splits into two molecules of pyruvate, which is 3-carbon, under the impact of enzymes to generate the required energy. This process can be described in two stages and several steps that are associated with each stage. It is also important to note that the process occurs in the cytoplasm of a cell, and its role is to guarantee the respiration under such conditions when oxygen is not available. The paper discusses these steps in detail.

The Process of Glycolysis

Glycolysis is a process of splitting 6-carbon glucose into two molecules of pyruvate, which is 3-carbon. This process is also known as the Embden-Meyerhof Pathway, and it involves several steps to cover all reactions (Mauseth, 2014, p. 245; Stoker, 2012). The process occurs in the cytosol of the cytoplasm of a cell (Stoker, 2012, p. 907). The significance of the process is in the fact that no oxygen is required for glycolysis, and this process is the first stage of generating or receiving the energy for anaerobic respiration of plants (Stoker, 2012).

During the first stage of glycolysis, the reaction is caused by adding a molecule of adenosine triphosphate or ATP to one of the phosphate groups. As a result, 6-carbon glucose is activated for further splitting (Mauseth, 2014). The result of this process is the glucose-6-phosphate (Mauseth, 2014, p. 247). At this stage, the forms of glucose are rather unstable, and they can further split as glucose becomes converted into fructose (Stoker, 2012). Another molecule of ATP also participates in the reaction while binding the other group of phosphates, and the result of these two reactions is the appearance of two 3-carbon molecules, also including dihydroxyacetone phosphate or DHAP and glyceraldehydes 3-phosphate or PGAL (Mauseth, 2014, p. 246; Stoker, 2012).

During the second stage of the process, DHAP becomes PGAL under the impact of associated processes and enzymes, and it is possible to observe two molecules of PGAL that participate in the reaction of oxidation, during which nicotinamide adenine dinucleotide or NADH is received, and the reaction of substrate-level phosphorylation, during which two molecules of ATP are formed (Stoker, 2012, p. 908). This number of ATP molecules also participated in the first phase of the reactions to activate the whole process. The phosphate groups continue to participate in reactions, and the next step is the process of dehydration (Stoker, 2012). The result of this process is phosphoenolpyruvate. During each step of the discussed two main processes, the reactions are catalyzed. Such enzymes as hexokinase, phosphoglucomutase, and aldolase which participate in different reactions also influence the processes discussed in these phases (Stoker, 2012).

The final result is the generation of four molecules of ATP, where two molecules are used for each of glucose molecules, two molecules of 3-carbon pyruvate, and the generation of two molecules of NADH (Stoker, 2012, p. 909). Still, two molecules of ATP were used for the first stage of the process. Thus, at the final stage, it is possible to speak about the presence of two molecules of ATP and two molecules of 3-carbon pyruvate as the main results of the discussed reactions (Mauseth, 2014, p. 246). These molecules are used to produce the energy for metabolic reactions that are characteristic of the anaerobic respiration process.

Mauseth, J. D. (2014). Botany . New York, NY: Jones & Bartlett Publishers.

Stoker, H. S. (2012). General, organic, and biological chemistry . New York, NY: Nelson Education.

Cite this paper

  • Chicago (N-B)
  • Chicago (A-D)

StudyCorgi. (2020, November 7). Glycolysis Process and Its Stages. https://studycorgi.com/glycolysis-process-and-its-stages/

"Glycolysis Process and Its Stages." StudyCorgi , 7 Nov. 2020, studycorgi.com/glycolysis-process-and-its-stages/.

StudyCorgi . (2020) 'Glycolysis Process and Its Stages'. 7 November.

1. StudyCorgi . "Glycolysis Process and Its Stages." November 7, 2020. https://studycorgi.com/glycolysis-process-and-its-stages/.

Bibliography

StudyCorgi . "Glycolysis Process and Its Stages." November 7, 2020. https://studycorgi.com/glycolysis-process-and-its-stages/.

StudyCorgi . 2020. "Glycolysis Process and Its Stages." November 7, 2020. https://studycorgi.com/glycolysis-process-and-its-stages/.

This paper, “Glycolysis Process and Its Stages”, was written and voluntary submitted to our free essay database by a straight-A student. Please ensure you properly reference the paper if you're using it to write your assignment.

Before publication, the StudyCorgi editorial team proofread and checked the paper to make sure it meets the highest standards in terms of grammar, punctuation, style, fact accuracy, copyright issues, and inclusive language. Last updated: November 7, 2020 .

If you are the author of this paper and no longer wish to have it published on StudyCorgi, request the removal . Please use the “ Donate your paper ” form to submit an essay.

U.S. flag

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

  • Publications
  • Account settings

Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now .

  • Advanced Search
  • Journal List

Compartmentalization and metabolic regulation of glycolysis

Hypoxia inhibits the tricarboxylic acid (TCA) cycle and leaves glycolysis as the primary metabolic pathway responsible for converting glucose into usable energy. However, the mechanisms that compensate for this loss in energy production due to TCA cycle inactivation remain poorly understood. Glycolysis enzymes are typically diffuse and soluble in the cytoplasm under normoxic conditions. In contrast, recent studies have revealed dynamic compartmentalization of glycolysis enzymes in response to hypoxic stress in yeast, C. elegans and mammalian cells. These messenger ribonucleoprotein (mRNP) structures, termed glycolytic (G) bodies in yeast, lack membrane enclosure and display properties of phase-separated biomolecular condensates. Disruption of condensate formation correlates with defects such as impaired synaptic function in C. elegans neurons and decreased glucose flux in yeast. Concentrating glycolysis enzymes into condensates may lead to their functioning as ‘metabolons’ that enhance rates of glucose utilization for increased energy production. Besides condensates, glycolysis enzymes functionally associate in other organisms and specific tissues through protein–protein interactions and membrane association. However, as discussed in this Review, the functional consequences of coalescing glycolytic machinery are only just beginning to be revealed. Through ongoing studies, we anticipate the physiological importance of metabolic regulation mediated by the compartmentalization of glycolysis enzymes will continue to emerge.

Summary: Glycolysis enzymes coalesce in non-membrane bound structures in response to energy stress in a wide variety of organisms. We review examples of this coalescence and evaluate what is known about the structure, function and formation of these structures.

Introduction

Glycolysis is a core energy-producing pathway in cells; it converts glucose to two net ATPs and pyruvates, which can then be utilized by the mitochondria to generate an additional 34 ATPs through oxidative phosphorylation in the tricarboxylic acid (TCA) cycle ( Al Tameemi et al., 2019 ) ( Fig. 1 ). Hypoxic stress precludes the function of the highly efficient oxidative phosphorylation pathway and limits energy production to glycolysis ( Al Tameemi et al., 2019 ). Despite substantial work on cellular adaptations to hypoxia, how cells compensate for this decreased energy efficiency is not fully understood. Normally, the ten core glycolysis enzymes are diffusely localized throughout the cytoplasm ( Huh et al., 2003 ) ( Fig. 1 ). However, under hypoxic conditions, glycolysis enzymes become compartmentalized into cytoplasmic structures ( Miura et al., 2013 ; Jang et al., 2016 ; Jin et al., 2017 ). For example, recent studies in yeast have revealed that glycolysis enzymes colocalize into glycolytic bodies (G bodies) in response to hypoxia, and analogous condensates form in Caenorhabditis elegans neurons ( Miura et al., 2013 ; Jang et al., 2016 ; Jin et al., 2017 ) ( Figs 2 – 4 ). Biophysical studies have demonstrated that these structures have properties of phase-separated condensates that are similar to those of stress granules and P bodies, thus joining a growing list of subcellular structures that are formed by phase separation ( Hyman et al., 2014 ; Fuller et al., 2020 ; Jang et al., 2021 ). Mutants unable to form these structures have decreased viability or synaptic function in yeast and worms, respectively ( Jang et al., 2016 ; Jin et al., 2017 ). The association of multiple glycolysis enzymes via phase separation may function to enhance the activity of the entire pathway and increase reaction rates critical for energy production, thereby forming a so-called ‘metabolon’ during hypoxic stress ( Srere, 1987 ; Miura et al., 2013 ; Jang et al., 2016 ; Jin et al., 2017 ). Similar structures also form in cancer cell lines, raising the as-yet-unexplored possibility that analogous G body structures in humans may promote cancer cell survival ( Jin et al., 2017 ). In this Review, we explore what is known about the structure, function and regulation of these glycolysis enzyme condensates, and highlight additional examples of compartmentalization of glycolysis enzymes.

An external file that holds a picture, illustration, etc.
Object name is joces-134-258469-g1.jpg

Glycolysis and related pathways. In the upstream glycolysis reactions, glucose is phosphorylated, isomerized to F6P, and phosphorylated once more, generating F16BP through the action of hexokinase (HXK), glucose phosphate isomerase (GPI) and phosphofructokinase (PFK), respectively. The reverse reaction of PFK is catalyzed by fructose-1,6-bisphosphatase (FBPase; not depicted). Next, F16BP is cleaved by aldolase (ALDO) into dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (GAP). DHAP can interconvert with GAP through triose phosphate isomerase (TPI) activity, thus generating two equivalents of GAP per molecule of glucose. In an NAD + -dependent reaction, glyceraldehyde phosphate dehydrogenase (GAPDH) converts GAP into 1,3-bisphosphoglycerate (13BPG). Phosphoglycerate kinase (PGK) generates ATP when converting 13BPG into 3-phosphoglycerate (3PG), which is then converted into 2-phosphoglycerate (2PG) by phosphoglycerate mutase. Enolase (ENO) converts 2PG into phosphoenolpyruvate (PEP), the substrate of the final glycolytic enzyme, pyruvate kinase (PYK) which generates ATP and pyruvate. The reverse of this reaction is catalyzed by phosphoenolpyruvate carboxykinase (PEPCK; not depicted). At multiple steps, metabolites can enter other pathways beginning with glucose phosphate, which can be directed into glycogen biosynthesis or the pentose phosphate pathway by phosphoglucomutase (PGM) or glucose-6-phosphate dehydrogenase (G6PDH), respectively. Downstream, 3PG can be directed into serine biogenesis. Pyruvate from glycolysis is either converted into ethanol (yeast) or lactic acid (metazoans) by fermentation in the cytoplasm or enters the TCA cycle in the mitochondria generating additional ATP. Glycolysis enzymes are indicated in green ovals and enzymes of related pathways appear in blue ovals.

An external file that holds a picture, illustration, etc.
Object name is joces-134-258469-g2.jpg

G body biogenesis, structure and composition. In normoxic conditions, glycolysis enzymes are diffuse throughout the cytoplasm, although they do associate with RNA (left). In hypoxia, RNA functions as a scaffold, promoting the formation of small complexes of glycolysis enzymes, RNA and additional non-glycolytic proteins. As cells remain in hypoxia, these small complexes fuse into large single granules that include additional proteins and are observable as bright foci with GFP-tagged reporters (right). G bodies are in close vicinity to other proteins despite lacking perfect overlap with their signals. Typical protein components are listed. G bodies have the physical properties of phase-separated gel-like granules as opposed to liquid assemblies, including stability in cell lysates, slow exchange with the cytosol, as measured in FRAP experiments, and slow fusion kinetics. Both the exchange of enzymes and fusion of single granules occurs on the timescale of minutes. RNA can modulate phase separation by several mechanisms (listed at bottom right).

An external file that holds a picture, illustration, etc.
Object name is joces-134-258469-g4.jpg

Pre-synaptic phase separation of glycolysis enzymes. Expanded view of an individual synaptic terminal in the neurosecretory motor neuron (NSM) of the pharynx of C. elegans . In normoxia, PFK-1.1 and ALDO-1 (green) are diffusely distributed, but within minutes of hypoxia occurring, they accumulate in condensates that are in close proximity with synaptic vesicles in a mutually dependent manner. GPD-3 (GAPDH) also localizes to these clusters. The condensates exhibit properties of liquid phase separation including the ability to fuse, fast dynamic formation and dissolution (within minutes of hypoxic treatment), fast exchange of proteins with the cytosol (measured by FRAP) and a propensity to become more solid as time in hypoxia increases. A dominant-negative allele of PFK-1.1 prevents this assembly, resulting in synaptic defects (bottom).

Protein composition of glycolytic granules

Of the glycolytic granules, yeast G bodies have the best-understood protein composition, based on proteomic studies that have been validated by in vivo colocalization of endogenous, fluorescently labeled candidate proteins residing in G bodies ( Fig. 2 ). Of the glycolysis enzymes, Eno2 (enolase), Pfk1 and Pfk2, the α- and β-subunits of yeast phosphofructokinase (PFK), respectively, Fba1 (aldolase) and Cdc19 (pyruvate kinase, PYK) strongly colocalize into a large single G body under hypoxic stress in yeast ( Miura et al., 2013 ; Jin et al., 2017 ). In C. elegans neurons, PFK, aldolase and glyceraldehyde-3-phosphate dehydrogenase (GPD-3; GAPDH) localize to glycolytic granules in hypoxia ( Jang et al., 2016 ). PFK, which catalyzes the rate-limiting ATP-dependent conversion of fructose-6-phosphate into fructose-1,6-bisphosphate, has been found in all glycolytic granules identified to date ( Miura et al., 2013 ; Jang et al., 2016 ; Kohnhorst et al., 2017 ; Jin et al., 2017 ) and serves as the canonical G body marker. Additional enzymes, including isoforms of GAPDH, PGK, phosphoglycerate mutase (PGM), Eno1 and Pyk2 localize to puncta resembling G bodies in a smaller subset of yeast cells ( Jin et al., 2017 ). In addition to the glycolysis enzymes, many other proteins localize to yeast G bodies to varying degrees. These include 26S proteasome subunits, components of other metabolic pathways, such as fatty acid metabolism and trehalose biosynthesis, translation elongation factors, ribosomal proteins, signaling factors and protein chaperones (e.g. Hsp70, Hsp42, and Hsp26), which localize to G bodies in nearly all cells ( Miura et al., 2013 ; Jin et al., 2017 ). Besides protein chaperones, which also localize to other condensates, including nucleoli during heat shock, and stress granules, where they are required for stress granule disassembly ( Walters et al., 2015 ; Jain et al., 2016 ; Frottin et al., 2019 ), most of these proteins only sparingly colocalize with G bodies, and they often appear in puncta adjacent to Pfk2-labeled G body foci. This suggests that G bodies are either complex structures with multiple subcompartments or they associate with other condensates or filaments ( Jin et al., 2017 ). Some of the proteins with weak colocalization, including several glycolysis enzymes, may only transiently localize to G bodies. Such dynamic recruitment of different sets of metabolic enzymes could rapidly reconfigure metabolism by altering the fate of glycolysis intermediates and the efficiency of individual steps of each reaction. Alternatively, the non-glycolytic proteins, such as proteasome subunits and translation-associated proteins, may be stably recruited to G bodies in a small fraction of cells. Finally, dynamic recruitment may indicate distinct stages of G body biogenesis. For instance, Eno2 foci precede the appearance of Cdc19 and PGM foci in hypoxic yeast, raising the possibility that Eno2 is required to form granules that subsequently recruit additional proteins ( Yoshimura et al., 2021 ). Studies of the dynamics of various G body proteins will be required to differentiate between these possibilities.

In cancer cell lines, both glycolytic and gluconeogenic enzymes localize to puncta called glucosomes ( Kohnhorst et al., 2017 ) ( Fig. 5 ). Furthermore, many enzymes are shared between the opposing gluconeogenesis and glycolysis pathways, with allosteric regulation of human phosphofructokinase (PFKL, glycolysis) and fructose-1,6-bisphosphatase (FBPase, gluconeogenesis) largely governing which pathway predominates ( Fig. 5 ). Both of these enzymes localize to glucosomes, in addition to phosphoenolpyruvate carboxykinase (PEPCK) and PYK ( Kohnhorst et al., 2017 ); therefore, allosteric regulation of these enzymes within granules may influence flux through the opposing pathways. While PFK puncta increase in size in hypoxia in HepG2 cells, it is unknown whether gluconeogenesis enzymes also localize to these large granules ( Jin et al., 2017 ). Proteomic analysis of glucosomes and hypoxic PFK puncta may help to define the composition of each granule. Are similar proteins recruited to these granules as to those in yeast G bodies? Do the larger hypoxic puncta comprise glucosomes that have fused or adjoined together, in which case there would be similar composition between the glucosome and hypoxic foci? Such studies may reveal principles of granule biogenesis and structure.

An external file that holds a picture, illustration, etc.
Object name is joces-134-258469-g5.jpg

Compartmentalization in mammalian cancer cells. (A) In HepG2 cells, a hepatocarcinoma-derived cell line, PFKL is localized in small clusters in normoxic conditions. Hypoxia generates large clusters of PFKL in an RNA-dependent manner as treatment with RNase prevents their formation. (B) Hypoxic conditions in the interior of solid tumors may induce an increase in the size of PFKL clusters to enhance glycolytic activity and promote survival. (C) Glucosomes, constitutive assemblies of glycolysis enzymes, are present in Hs578T cells and other cancer cell lines even in the absence of hypoxia. Treatment with metabolites that promote alternative glucose utilization pathways (serine biosynthesis or the pentose phosphate pathway) leads to changes in granule size which may correlate with flux of metabolites into these alternative pathways. Glucosomes may be identical with the small PFKL clusters in A. (D) Glucosomes contain both glycolytic and gluconeogenic enzymes, allowing potential control of glycolytic and gluconeogenic flux through PFKL (glycolysis) or FBPase (gluconeogenesis) activity via conversion of F6P and F16BP. Downstream reactions can promote gluconeogenesis by conversion of oxaloacetate from the TCA cycle to PEP via PEPCK or complete glycolysis by conversion of PEP into pyruvate and ATP catalyzed by PYK.

Protein–protein interactions are likely important for localization to glycolytic granules. In C. elegans glycolytic condensates, aldolase (ALDO-1) and PFK (PFK-1.1) recruitment are mutually dependent ( Fig. 4 ) ( Jang et al., 2021 ). Moreover, many glycolysis enzymes function in quaternary structures; for example, PFK is an octamer ( Sträter et al., 2011 ; Schöneberg et al., 2013 ). In yeast, this octamer is comprised of four α (Pfk1) and four β (Pfk2) subunits, stabilized by interactions between each set of subunits ( Banaszak et al., 2011 ; Sträter et al., 2011 ). The multiple interactions between domains of human PFKL monomers facilitate filamentation, which is morphologically distinct from spherical condensates typical of G bodies and C. elegans glycolytic condensates ( Jang et al., 2016 ; Webb et al., 2017 ; Jin et al., 2017 ). In yeast, several glycolysis enzymes form filaments, including Cdc19, Pfk1 and Pfk2, and glucokinase (Glk1), although the relationship between filamentation and spherical granule formation remains unclear ( Shen et al., 2016 ; Noree et al., 2019 ; Stoddard et al., 2020 ). Filaments could act as scaffolds that recruit additional enzymes. Glycolysis enzymes, including hexokinase (HXK), triose phosphate isomerase (TPI), glucose phosphate isomerase (GPI), aldolase, GAPDH and enolase associate with F-actin, which acts as a scaffold, in yeast, promoting interactions between glycolysis enzymes ( Waingeh et al., 2006 ; Araiza-Olivera et al., 2013 ). Importantly, the actin-associated enzymes only partially overlap with G body proteins and thus likely represent a distinct complex. Moreover, the strongest interaction between actin and a glycolysis enzyme is with GAPDH ( Waingeh et al., 2006 ). In contrast, GAPDH only rarely localizes to G bodies, highlighting the different composition of each complex. Finally, the biophysical properties of actin-associated glycolysis enzyme complexes in yeast have yet to be explored and they may not constitute condensates. Yeast Glk1 filamentation resembles folding of actin ( Stoddard et al., 2020 ). By mimicking the shape of F-actin, glucokinase may provide similar binding sites to function as a scaffold for additional glycolysis enzymes, although this possibility has not yet been explored.

Characterization of the proteomes of glycolytic granules from different species will be important for understanding the overall composition and potential function of these granules. Additionally, studies comparing granule composition under various environmental conditions will elucidate dynamic protein recruitment to glycolytic granules. Finally, evaluating granule composition in mutants, in which different granule components are deleted, will help identify the genetic requirements for granule assembly, structure, maintenance and regulation.

Phase separation of glycolysis enzymes

Recently, phase separation has emerged as an organizing process that can rapidly concentrate specific proteins and RNAs in structures termed ‘condensates’ in response to a variety of environmental cues ( Hyman et al., 2014 ). Condensates form with a range of physical properties, from those resembling liquid droplets, such as nucleoli and yeast P bodies, to solid gels, such as yeast stress granules, while other condensates possess both gel- and liquid-like components ( Brangwynne et al., 2011 ; Kroschwald et al., 2015 ; Jain et al., 2016 ; Putnam et al., 2019 ). For example, in C. elegans P granules, MEG-3 adopts a gel phase to serve as a solid scaffold for PGL-3, which has more liquid-like properties ( Putnam et al., 2019 ).

Several lines of evidence suggest that G bodies in yeast and glycolysis enzyme structures in C. elegans neurons are condensates formed via phase separation but possess distinct physical properties ( Fig. 2 ). First, G bodies lack membranes, as revealed by electron microscopy ( Jin et al., 2017 ). Second, recruitment of Pfk2 to G bodies relies on multivalent interactions through both its N- and C-terminal regions, which are connected by a disordered linker ( Sträter et al., 2011 ; Fuller et al., 2020 ). Third, G bodies in a and α yeast cells can fuse during mating ( Fuller et al., 2020 ). Consistent with the slow (10–20 min) recovery kinetics measured by fluorescence recovery after photobleaching (FRAP), G bodies within mating cells fuse slowly, often taking many minutes for two smaller granules to form into a single large G body ( Fuller et al., 2020 ). In contrast, liquid-like P bodies fuse within seconds of contact and have components that display near full FRAP recovery within seconds ( Kroschwald et al., 2015 ). In C. elegans , hypoxia-induced assemblies of glycolysis enzymes have more liquid-like properties than their yeast counterparts, fusing within two seconds of contact ( Jang et al., 2021 ). Similar fusion timescales have been observed for PFKL in cell culture overexpression experiments ( Webb et al., 2017 ). Unlike in yeast, C. elegans hypoxic condensates display strong FRAP recovery, within tens of seconds, although there is less recovery with prolonged exposure to hypoxic conditions, indicating a transition to a more gel-like state ( Jang et al., 2021 ) ( Fig. 4 ). A fourth line of evidence that G bodies form via phase separation is that their size decreases following treatment with the aliphatic alcohol 1,6-hexanediol, although G bodies do not completely dissolve ( Fuller et al., 2020 ). It is tempting to speculate that partial dissolution may reflect a dynamic shell around G bodies, akin to what is present on stress granules ( Jain et al., 2016 ). A dynamic shell could explain the variation in colocalization observed for different G body components ( Jin et al., 2017 ). Fifth, the initial formation of granules in C. elegans occurs in regions of the axon with high local concentrations of PFK-1.1, indicating that it has a propensity to phase separate in a concentration-dependent manner ( Jang et al., 2021 ). Finally, G bodies appear stable and can be biochemically purified from a cell lysate, rather than dissolving in dilute conditions ( Miura et al., 2013 ; Jin et al., 2017 ; Fuller et al., 2020 ). Thus, in yeast, G bodies appear to form gels that maintain their structure, even when moved to a dilute medium, exchange proteins with the cytoplasm and fuse slowly, while C. elegans granules are more fluid and dynamic. However, even in yeast, multiple smaller foci are initially observed prior to the appearance of a single G body per cell upon extended periods in hypoxia, suggesting that these smaller puncta fuse to form the larger mature G body ( Jin et al., 2017 ). Therefore, liquid states could precede the gel-like state of G bodies, as has been observed in disease states for stress granules and in C. elegans hypoxic granules ( Patel et al., 2015 ; Murakami et al., 2015 ; Bolognesi et al., 2016 ; Mateju et al., 2017 ; Fuller et al., 2020 ; Jang et al., 2021 ).

The differences in physical properties between yeast G bodies and C. elegans PFK-1.1 condensates mirror the differing material properties between yeast stress granules, which resemble solid aggregates, and mammalian stress granules, which resemble a viscous liquid ( Kroschwald et al., 2015 ). One possible explanation for the discrepancy in material properties is that yeast G bodies require many hours to form, whereas C. elegans PFK-1.1 condensates form quickly within 10 min under hypoxia. Therefore, the prolonged period required to form yeast G bodies may provide the time for these condensates to mature from a liquid to gel-like state ( Jang et al., 2016 ; Jin et al., 2017 ; Jang et al., 2021 ). Moreover, extended periods in hypoxia lead to a decreased amplitude, but not half time, of PFK-1.1 FRAP recovery in granules ( Jang et al., 2021 ). Thus, C. elegans granules and yeast G bodies may form via a similar mechanism, but the latter represents a much later stage of maturation in the liquid-to-solid transition.

Interestingly, the yeast Cdc19 PYK accumulates in stress granules during glucose starvation, likely through phase separation that is dependent on an intrinsically disordered region in the enzyme ( Saad et al., 2017 ; Grignaschi et al., 2018 ). However, neither G bodies nor PFK-1.1 condensates in C. elegans neurons seem to contain the stress granule markers Pab1 and TIAR, respectively ( Jin et al., 2017 ; Jang et al., 2021 ). Thus, these hypoxia-induced granules are distinct from stress granules, and Cdc19 recruitment under hypoxic conditions may have a different role rather than just its sequestration.

The role of RNA in G body formation and structure

Like other condensates, RNA localizes to G bodies. Most known G body proteins can bind to RNA, despite lacking canonical RNA-binding domains ( Fuller et al., 2020 ). Sequencing of mRNAs crosslinked to purified messenger ribonucleoprotein (mRNP) complexes has revealed that most glycolysis enzymes bind RNA in normoxic conditions ( Castello et al., 2012 ; Beckmann et al., 2015 ; Matia-González et al., 2015 ; Fuller et al., 2020 ). RNA binding by glycolysis enzymes is highly conserved in bacteria, plants and metazoans ( Sysoev et al., 2016 ; Despic et al., 2017 ; Albihlal and Gerber, 2018 ; Huang et al., 2018 ; Shchepachev et al., 2019 ). Included among the hundreds of distinct transcripts bound by glycolysis enzymes are those of the glycolysis enzymes themselves, which have a large number of experimentally validated protein-binding sites ( Freeberg et al., 2013 ; Shchepachev et al., 2019 ; Fuller et al., 2020 ). Targeting RNases to sites of G body formation prevents G bodies from forming, indicating that RNA is required for their nucleation. Moreover, targeting RNases to existing G bodies causes them to fracture into multiple smaller granules, suggesting that RNA stabilizes mature condensates ( Fuller et al., 2020 ).

RNA could contribute to G body formation by concentrating and sequestering protein components through multiple binding sites (i.e. multivalency), thereby acting as a scaffold ( Garcia-Jove Navarro et al., 2019 ; Dutagaci et al., 2021 ) ( Fig. 2 ). Specific mRNA–protein interactions can be important for condensate formation. For example, in vitro , the yeast Whi3 protein partitions into either gel or liquid droplets depending on which of its mRNA substrates is available through interactions largely driven by secondary structure ( Zhang et al., 2015 ; Langdon et al., 2018 ). Moreover, RNA alone can phase separate, and specific homotypic RNA–RNA interactions are emerging as an organizing principle in germ granule composition in Drosophila melanogaster ( Trcek et al., 2015 , 2020 ; Jain and Vale, 2017 ; Van Treeck et al., 2018 ). In contrast, nonspecific interactions between RNA and intrinsically disordered regions can also drive phase separation ( Protter et al., 2018 ).

Whether specific protein–mRNA interactions underlie RNA-mediated G body formation is unclear. Sequencing of G body RNAs and localization by single-molecule fluorescence in situ hybridization (smFISH) demonstrate that many different RNAs reside in G bodies, although only a small fraction (<2%) of a given mRNA species localizes to G bodies ( Fuller et al., 2020 ). Despite the fact that small quantities of particular mRNA species are concentrated, there is a wide variability in mRNA enrichment in G bodies. G body RNAs show a substantial, but incomplete, overlap with RNAs bound by glycolysis enzymes in normoxic conditions, suggesting that glycolysis enzymes are bound by RNA in the cytoplasm and then recruited to G bodies together ( Fuller et al., 2020 ). The lack of complete overlap could be due to the presence of other RNA binding proteins in G bodies or altered RNA binding in hypoxic conditions. In yeast, altered environmental conditions, such as glucose or nitrogen starvation, lead to substantial changes in protein occupancy on mRNAs, including those of G body-associated mRNAs and glycolysis enzyme mRNAs themselves ( Freeberg et al., 2013 ). Additional studies will be necessary to determine whether specific mRNA–protein and RNA–RNA interactions are required for G body structure and formation.

While P bodies and stress granules incorporate a large fraction of the transcriptome, they recruit certain mRNAs to a far larger extent than others, indicating some degree of specificity in recruitment ( Hubstenberger et al., 2017 ; Khong et al., 2017 ). For example, unlike in G bodies, which recruit at most 2% of a single mRNA species, up to 95% of certain mRNA species, such as AHNAK and DYNC1H1 , localize to stress granules ( Khong et al., 2017 ). However, most stress granule mRNAs are enriched in stress granules relative to the cytoplasm to a lesser extent. mRNAs in stress granules and P bodies are poorly translated ( Khong et al., 2017 ). However, given that the bulk of each of the mRNAs identified in G bodies localizes elsewhere, it seems unlikely that the minor fraction sequestered into G bodies significantly impacts the overall translational output of the mRNA for a specific protein. Nevertheless, additional studies will be required to determine the fate of mRNAs that localize to G bodies.

Regulation of G body assembly

Stress induces the formation of many condensates within the cell, such as stress granules, P bodies and inclusion bodies. As previously mentioned, hypoxic stress, in particular, induces the self-association of glycolysis enzymes into large granules in yeast, C. elegans and human cancer cells ( Figs 2 , ​ ,4 4 and ​ and5) 5 ) ( Miura et al., 2013 ; Jang et al., 2016 ; Jin et al., 2017 ). Several genetic determinants of G body assembly have been identified and implicate energy-sensing homeostasis pathways in G body regulation ( Fig. 3 ). In particular, rapamycin treatment, which inhibits TORC1, the complex in yeast homologous to the mammalian target of rapamycin complex (mTORC1), prevents the formation of Eno2–GFP puncta in yeast, demonstrating that TORC1 activity is required for G body formation ( Miura et al., 2013 ). Additionally, Ira2, a negative regulator of the pro-growth yeast RAS/cAMP pathway, which activates the downstream protein kinase A (PKA), localizes to G bodies in less than 2% of cells and is required for their formation, although it is unknown whether this requirement is due to signaling or direct physical interactions ( Jin et al., 2017 ). Finally, the AMP-activated protein kinase Snf1, which is activated in response to high AMP-to-ATP ratios and promotes glycolytic activity, is required for normal G body formation in yeast ( Miura et al., 2013 ; Jin et al., 2017 ; Yoshimura et al., 2021 ). By controlling protein synthesis, TORC1 and PKA may modify the proteomic response to hypoxia, thereby affecting G body formation. Alternatively, these factors may directly phosphorylate G body proteins or regulators and control the association of G body enzymes. However, while Pfk2 is progressively phosphorylated in a Snf1-dependent manner in hypoxia, Pfk2 localization to G bodies appears to be independent of its phosphorylation ( Jin et al., 2017 ).

An external file that holds a picture, illustration, etc.
Object name is joces-134-258469-g3.jpg

Genetic regulation of G body formation. Hypoxia triggers activation of signaling pathways that are involved in energy homeostasis and required for G body formation (shown on the left). Inhibition of the TORC1 complex by rapamycin treatment prohibits G body formation. In addition to TORC1, Snf1, the yeast ortholog of the AMP-activated protein kinase (AMPK), and Ira2, a negative regulator of the pro-growth pathway (RAS to PKA), is required for G body formation. Hypoxia also triggers the production of superoxide radicals through mitochondrial dysfunction, and the expression of Sod1, the cytoplasmic enzyme that degrades superoxide radicals, is involved in G body formation. Many of the glycolysis enzymes strongly localize to G bodies, including the sequential set of enzymes, PFK and aldolase (see diagram on the right). However, TPI and GAPDH do not strongly localize to G bodies, suggesting the reactions they catalyze occur in the cytoplasm. Downstream of GAPDH, enolase and PYK, catalyzing the final two steps of glycolysis, localize to G bodies, suggesting that both the upstream and far downstream reactions occur in G bodies.

G body formation has also been linked to mitochondrial function, given that mitochondrial inhibitors, such as antimycin or CCCP, disrupt Eno2–GFP localization to G bodies ( Miura et al., 2013 ). This inhibition could be related to the generation of mitochondrial reactive oxygen species (ROS) that occurs upon a shift to hypoxia ( Görlach et al., 2015 ). N-acetyl cysteine, an antioxidant, also inhibits the formation of Eno2–GFP foci ( Miura et al., 2013 ). Moreover, Sod1, the primary superoxide dismutase in yeast, localizes to G bodies at a low frequency and is required for G body formation ( Fig. 3 ) ( Jin et al., 2017 ). Further studies will be required to determine the molecular mechanisms by which these pathways regulate G body formation, and whether they also impact the formation of G body-like structures in C. elegans and mammalian cells.

Finally, granule formation may be sensitive to the metabolic needs of a cell. Glucosome size in mammalian cancer cell lines in normoxic conditions varies depending on addition of metabolites that differentially promote glucose flux, the pentose phosphate pathway or serine synthesis ( Fig. 5 ) ( Kohnhorst et al., 2017 ). Similarly, G body formation in yeast requires glucose ( Jin et al., 2017 ). Therefore, the composition of glycolysis enzyme granules may vary depending on available nutrients. G bodies can recruit a number of different metabolic enzymes, including the enzymes of fatty acid synthesis ( Jin et al., 2017 ). Some of these enzymes and G body RNAs are recruited to the periphery of the G body rather than perfectly overlapping with G body markers, possibly indicating transient association with these granules ( Jin et al., 2017 ; Fuller et al., 2020 ). It is interesting to speculate that compositional changes of these assemblies, in response to altered nutrient availability, could promote activity of pathways besides glycolysis by supplying ATP or substrates.

Physiological function of glycolysis enzyme granules

A variety of functions have been proposed for glycolytic granules. Mutant C. elegans strains lacking the ability to form condensates have decreased synaptic function ( Jang et al., 2016 ). Loss of PFK-1.1, the primary PFK isoform in C. elegans neurons, leads to disruption of presynaptic vesicle clustering specifically during hypoxia at the same location where the condensates form ( Jang et al., 2016 ). Overexpression of a dominant-negative allele that impairs PFK-1.1 localization also results in similar defects in vesicle clustering and loss of pfk-1.1 causes decreased recovery of synapses ( Fig. 4 ) ( Jang et al., 2016 ). Thus, condensate formation in C. elegans neurons may occur to enhance glycolytic rates during energy stress to maintain synaptic transmission between neurons.

In yeast, mutants unable to form G bodies display decreased glucose flux and accumulate upstream glycolysis metabolites ( Miura et al., 2013 ; Jin et al., 2017 ). Normoxic cells with diffuse glycolysis enzymes consume glucose at a slower rate than cells taken from hypoxia that have G bodies ( Jin et al., 2017 ). Finally, cells lacking G bodies are at a competitive growth disadvantage compared to cells that are able to form G bodies ( Fuller et al., 2020 ). The phenotypes of cells lacking G bodies suggest that glycolysis enzymes phase separate to enhance energy production and promote cell survival ( Fig. 3 ). These physiological findings make it unlikely that G bodies are aggregates of misfolded and inactive proteins, as is the case for other compartments, such as insoluble protein deposits (IPODS), juxta-nuclear quality control compartments (JUNQs), or aggresomes ( Rothe et al., 2018 ). Direct measurements of enzyme activity in purified G bodies are needed to confirm that this is the case.

If G body-mediated enhancement of glucose flux is conserved in human cancer-derived cells, glycolytic granules could promote hypoxic cell survival and proliferation in the hypoxic environment of solid tumors ( Petrova et al., 2018 ; Al Tameemi et al., 2019 ). Clustering of glycolysis enzymes in glucosomes is constitutive in several cancer cell lines, but is modified under conditions affecting energy production ( Kohnhorst et al., 2017 ; Jin et al., 2017 ). In particular, hypoxia, which creates energy stress by depriving cells of respiration, enhances clustering of PFKL in the HepG2 hepatocarcinoma-derived cell line ( Jin et al., 2017 ). Thus, clustering may function as a method to enhance pathway activity when energy production is limited. Indeed, hypoxic exposure has been shown to enhance cancer cell proliferation ( Das et al., 2008 ). Moreover, glucosomes may have a role in normoxic conditions to enhance cancer cell viability ( Kohnhorst et al., 2017 ). One possibility is that condensates of glycolysis enzymes promote Warburg metabolism, or aerobic glycolysis, in which cancer cells primarily utilize glycolysis and fermentation rather than respiration through the TCA cycle to generate ATP ( Potter et al., 2016 ). Hypoxic exposure could promote the formation of granules that subsequently promote proliferation and cancer metabolism in normoxic conditions.

Enzyme activity in glycolytic granules

Enzyme activity may be modulated in assemblies of enzymes in condensates. For example, yeast aminoacylation enzymes aggregate in heat shock but maintain their activity ( Wallace et al., 2015 ). Clustered glycolysis enzymes may function to enhance glycolytic rates through several possible mechanisms, including concentrating metabolites, altering enzyme reaction rates or directly supporting substrate channeling, whereby sequential enzymes associate with one another so that they can directly transfer the product of the first reaction to the second enzyme as its substrate. Enzyme reaction rates can vary substantially for glycolysis enzymes, especially PFK, which is subject to both activating and inhibitory allosteric regulation ( Locasale, 2018 ). Formation of large complexes can affect metabolic enzyme activity. For instance, acetyl-CoA carboxylase can increase its reaction rates when forming filaments, whereas yeast glucokinase is strongly inhibited and held in an inactive conformation in filaments ( Kleinschmidt et al., 1969 ; Stoddard et al., 2020 ; Park and Horton, 2019 ). Similarly, enzymes in condensates may adopt conformations that either favor or disfavor their activity. Alternatively, substrates may partition differentially in the cytosol and condensate phase. In vitro , dextranase partitioned in a multi-phase droplet system has increased activity due to the concentration of substrate in another phase, thereby relieving substrate inhibition ( Kojima and Takayama, 2018 ). Moreover, pyrenoids, liquid condensates of RuBisCo involved in carbon fixation in green algae, enhance reaction rates and oppose a futile reverse reaction by concentrating the substrate, CO 2 , in the condensate ( Freeman Rosenzweig et al., 2017 ; Wunder et al., 2018 ). Some of the many glycolysis metabolites may become concentrated in granules, or inhibitors such as ATP may be excluded, achieving similar results. One final possibility is that glycolysis enzymes may form a metabolon that supports substrate channeling ( Srere, 1987 ). This limits diffusion and potential utilization by other cellular processes, and can enhance reaction rates for enzymes with extremely high turnover rates or low concentrations of substrate ( Sweetlove and Fernie, 2018 ). Indeed, the low substrate availability after the extended periods (>12 h) of hypoxia that are required for G body formation in yeast may necessitate substrate channeling ( Jin et al., 2017 ). Another condensate, the purinosome, which forms in response to purine depletion in mammalian cells and is comprised of purine biosynthesis enzymes, may function through substrate channeling ( An et al., 2008 ). Through a combination of isotope labeling experiments and a novel in situ mass spectrometry approach, purinosomes have recently been shown to concentrate purine biosynthesis intermediates in vivo and support substrate channeling ( Pareek et al., 2020 ). Similar methods may be applicable to studying condensates of glycolysis enzymes and reveal functional mechanisms.

Other forms of compartmentalization of glycolysis enzymes

In metazoans, several glycolysis enzymes colocalize in muscle tissue ( Clarke and Masters, 1975 ; Menard et al., 2014 ). A striking example of the importance of this association has been observed in D. melanogaster flight muscle ( Fig. 6 A). GAPDH, aldolase, PGK, PGM, TPI and glycerol phosphate dehydrogenase (GPDH) all localize to muscle fibers in flight muscle tissue ( Wojtas et al., 1997 ; Sullivan et al., 2003 ). Mutants lacking the muscle-specific isoform of GPDH fail to recruit the other enzymes to sarcomeres ( Wojtas et al., 1997 ; Sullivan et al., 2003 ). Expression of a separate GPDH isoform fails to rescue sarcomere recruitment of glycolysis enzymes in the absence of the muscle isoform and results in a loss of the ability to fly, indicating that recruitment of these enzymes to sarcomeres promotes muscle function ( Wojtas et al., 1997 ). In contrast, disruption of most of the individual glycolysis enzymes by P-element excision leads to only a small or no change in wing beat frequency, a measure of the function of flight muscle, while GPDH disruption decreases wing beat frequency ( Eanes et al., 2006 ; Merritt et al., 2006 ). The association of these enzymes with actin may aid their recruitment, but is unlikely to scaffold these complexes due to the lack of actin in M-lines and Z-lines ( Waingeh et al., 2006 ; Lange et al., 2020 ). Alternatively, GPDH may directly recruit additional enzymes and itself interact with proteins at M- and Z-lines, although this possibility has not yet been reported. Several pairs of sequential pathway enzymes, including TPI and GAPDH, and PGK and PGM, localize to M-lines and Z-lines of sarcomeres ( Fig. 6 A), although there is no direct evidence of substrate channeling, which would require in vitro measurements of activity of Z-line and M-line-associated glycolysis enzymes ( Sullivan et al., 2003 ). Thus, concentration of these enzymes may power flight muscle by converting a local high-concentration pool of metabolites into usable energy or by directly interacting with flight muscle at a low copy number. Alternatively, flight muscle glycolysis enzymes may facilitate mitochondrial activity. Analysis of additional enzyme localization, studies of mutants with impaired localization but not activity, and reconstitution of enzyme activity in this muscle tissue system would clarify function and test whether M-line association of glycolysis enzymes supports substrate channeling and constitutes a metabolon.

An external file that holds a picture, illustration, etc.
Object name is joces-134-258469-g6.jpg

Non-condensate compartmentalization in plants and insects. (A) Colocalization of glycolysis enzymes in D. melanogaster flight muscle fibers. M-lines and Z-lines associate with glycolysis enzymes (indicated with blue). Glycolysis enzymes associated with Z-lines are shown on the right. In the presence of GPDH, multiple sequential glycolysis enzymes associate with the Z-line, allowing them to convert fructose-1,6-bisphosphate to ATP and pyruvate. Deletion of muscle GPDH disrupts localization of the other glycolysis enzymes, resulting in flight defects. (B) Substrate channeling on the mitochondrial membrane in plants. In Arabidopsis thaliana , glycolysis enzymes (yellow, blue and purple shapes) are diffusely localized in the cytosol. Inhibition of respiration triggers the accumulation of each glycolysis enzyme on mitochondrial membranes. These complexes promote substrate channeling through the glycolytic pathway, efficiently converting glucose into usable ATP.

In addition, glycolysis enzymes have been found to directly interact with mitochondria in a number of circumstances. Mitochondria in yeast co-purify with glycolysis enzymes, including HXK ( Morgenstern et al., 2017 ). Moreover, in plants such as Arabidopsis thaliana , functional glycolysis enzymes both associate with the mitochondria and reside in the cytosol ( Fig. 6 B) ( Giegé et al., 2003 ). Mitochondrial association of glycolysis enzymes has been linked to mitochondria–chloroplast interactions ( Zhang et al., 2020 ). Activity of all glycolysis enzymes is detected in mitochondrial fractions. The amount of mitochondria-associated glycolytic activity increases when respiration is inhibited – especially for downstream enzymes – indicating that this localization may function to enhance energy production when respiration is limited ( Graham et al., 2007 ). In support of this hypothesis, isotope labeling experiments measuring activity of glycolysis enzymes associated with mitochondria indicate that the glycolysis enzymes on mitochondria can support direct substrate channeling ( Fig. 6 B) ( Graham et al., 2007 ; Zhang et al., 2020 ). Dilution with unlabeled glycolysis intermediates led to either no decrease or less than expected decreases in the rate of accumulation of 13 C-labeled glycolysis intermediates derived from [ 13 C]glucose (or [ 13 C]F16BP), indicating that metabolites were efficiently channeled through sequential reactions and not outcompeted by freely diffusing unlabeled intermediates ( Graham et al., 2007 ). The downstream reactions converting 2-phosphoglycerate (2PG) into phosphoenolpyruvate (PEP) then pyruvate also appear to be channeled using the same approach ( Zhang et al., 2020 ). These sequential downstream glycolysis enzymes – PGM, enolase and PYK – form a specific complex on mitochondria and achieve a 20-fold increase in catalytic efficiency ( Zhang et al., 2020 ). Thus, glycolysis enzymes can support substrate channeling when concentrated on mitochondrial membranes.

The glycolysis enzymes are also able to associate with the plasma membrane in erythrocytes, a cell type solely reliant on glycolysis for energy production, in both mouse and humans ( Campenella et al., 2005 , 2008 ; Puchulu-Campenella et al., 2013 ). PFK, aldolase, GAPDH, PYK and lactate dehydrogenase all associate on the membrane only in normoxic conditions, unlike in G bodies and C. elegans neuronal condensates ( Campenella et al., 2005 ). These enzymes are recruited through interactions with the membrane protein, band 3 ( Campenella et al., 2005 ; Puchulu-Campenella et al., 2013 ).

Finally, glycolysis enzymes are organized in membrane-bound compartments related to peroxisomes, called glycosomes, in a variety of organisms, including Trypanosomes ( Quiñones et al., 2020 ). These structures have been extensively reviewed ( Michels et al., 2005 , 2021 ; Haanstra et al., 2016 ) and require transport in membrane-bound compartments rather than relying on protein–protein or RNA–protein interactions to form and are beyond the scope of this Review.

Outlook and future directions

Evidence is mounting that glycolysis enzymes associate with one another in certain contexts. Compartmentalization is often induced by environmental stimuli requiring increased energy output, such as hypoxia or in the presence of respiratory chain inhibitors ( Graham et al., 2007 ; Miura et al., 2013 ; Jang et al., 2016 ; Jin et al., 2017 ; Fuller et al., 2020 ; Yoshimura et al., 2021 ). In other cases, compartmentalization is constitutive in tissues with high energy demands, although it may also relate to disease states in cancer cell lines ( Wojtas et al., 1997 ; Kohnhorst et al., 2017 ). However, our understanding of the function and pervasiveness of this phenomenon is hampered by a dearth of examples, all from widely different systems, and a reliance on correlative data. The mechanisms governing formation of these structures may widely vary. While condensate formation by phase separation appears to be responsible for yeast G bodies and C. elegans neuronal granules , phase separation has not been tested as an organizing process for other glycolysis enzyme structures. Formation of soluble, multienzyme complexes could occur without relying on phase separation. Even membrane-bound compartments of glycolysis enzymes can form (i.e. the glycosome), demonstrating a variety of strategies to concentrate glycolysis enzymes.

Even in yeast, we are only beginning to understand the pathways regulating glycolytic compartmentalization. Future studies in yeast and other organisms will be required to define the genetics of G body formation and function. Furthermore, there is evidence that composition within granules changes in various environments, although the underlying genetics and functional significance of these changes is unclear ( Kohnhorst et al., 2017 ; Jin et al., 2017 ). Furthermore, our understanding of the function of these condensates is minimal. With a few notable exceptions ( Graham et al., 2007 ), direct substrate channeling has not been observed and understanding the function and mechanism of the condensates will require biochemical reconstitution of glycolytic activity in glycolytic granules or adaptation of novel methods to observe metabolites and glycolysis enzyme activity in vivo ( Pareek et al., 2020 ). Finally, the observation that glycolysis enzymes form granules in cancer cells raises the possibility that compartmentalization of glycolysis enzymes is related to cancer progression and promotes Warburg metabolism. Exploration of this intriguing hypothesis is important and will be aided by a better understanding of genetic regulation in other systems to facilitate physiological studies in vitro and in vivo .

Acknowledgements

The authors thank Amelia Alessi, Mindy Clark and Margaret Starostik of the Kim laboratory for helpful comments.

Competing interests

The authors declare no competing or financial interests.

Our work is supported by a grant from the National Institutes of Health (NIH) R01 GM129301. Deposited in PMC for release after 12 months.

  • Al Tameemi, W., Dale, T. P., Al-Jumaily, R. M. K. and Forsyth, N. R. (2019). Hypoxia-modified cancer cell metabolism . Front. Cell Dev. Biol. 7 , 4. 10.3389/fcell.2019.00004 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Albihlal, W. S. and Gerber, A. P. (2018). Unconventional RNA–binding proteins: an uncharted zone in RNA biology . FEBS Lett. 592 , 2917-2931. 10.1002/1873-3468.13161 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • An, S., Kumar, R., Sheets, E. D. and Benkovic, S. J. (2008). Reversible compartmentalization of de novo purine biosynthetic complexes in living cells . Science 320 , 103-106. 10.1126/science.1152241 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Araiza-Olivera, D., Chiquete-Felix, N., Uribe-Carvajal, S., Sampedro, J. G., Peña, A., Mujica, A. and Uribe-Carvajal, S. (2013). In Saccharomyces cerevisiae a glycolytic metabolon is stabilized by F-Actin . FEBS J. 280 , 3887-3905. 10.1111/febs.12387 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Banaszak, K., Mechin, I., Obmolova, G., Oldham, M., Chang, S. H., Ruiz, T., Radermacher, M., Kopperschläger, G. and Rypniewski, W. (2011). The crystal structures of eukaryotic phosphofructokinases from baker's yeast and rabbit skeletal muscle . J. Mol. Biol. 407 , 284-297. 10.1016/j.jmb.2011.01.019 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Beckmann, B. M., Horos, R., Fischer, B., Castello, A., Eichelbaum, K., Alleaume, A.-M., Schwarzl, T., Curk, T., Foehr, S., Huber, W.et al. (2015). The RNA-binding proteomes from yeast to man harbour conserved enigmRBPs . Nat. Commun. 6 , 10127. 10.1038/ncomms10127 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Bolognesi, B., Lorenzo Gotor, N., Dhar, R., Cirillo, D., Baldrighi, M., Tartaglia, G. G. and Lehner, B. (2016). A concentration-dependent liquid phase separation can cause toxicity upon increased protein expression . Cell Reports 16 , 222-231. 10.1016/j.celrep.2016.05.076 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Brangwynne, C. P., Mitchison, T. J. and Hyman, A. A. (2011). Active liquid-like behavior of nucleoli determines their size and shape in Xenopus laevis oocytes . Proc. Natl Acad. Sci. USA 108 , 4334-4339. 10.1073/pnas.1017150108 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Campenella, M. E., Chu, H. and Low, P. (2005). Assembly and regulation of a glycolytic enzyme complex on the human erythrocyte membrane . Proc. Natl Acad. Sci. USA 102 , 2402-2407. 10.1073/pnas.0409741102 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Campenella, M. E., Chu, H., Wandersee, N. J., Peters, L. L., Mohandas, N., Gilligan, D. M. and Low, P. S. (2008). Characterization of glycolytic enzyme interactions with murine erythrocyte membranes in wild-type and membrane protein knockout mice . Blood 112 , 3900-3906. 10.1182/blood-2008-03-146159 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Castello, A., Fischer, B., Eichelbaum, K., Horos, R., Beckmann, B. M., Strein, C., Davey, N. E., Humphreys, D. T., Preiss, T., Steinmetz, L. M.et al. (2012). Insights into RNA biology from an atlas of mammalian mRNA-binding proteins . Cell 149 , 1393-1406. 10.1016/j.cell.2012.04.031 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Clarke, F. M. and Masters, C. J. (1975). On the association of glycolytic enzymes with structural proteins of skeletal muscle . Biochim. Biophys. Acta 381 , 37-46. 10.1016/0304-4165(75)90187-7 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Das, S., Srikanth, M. and Kessler, J. A. (2008). Cancer stem cells and glioma . Nat. Clin. Pract. Neurol. 4 , 427-435. 10.1038/ncpneuro0862 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Despic, V., Dejung, M., Gu, M., Krishnan, J., Zhang, J., Herzel, L., Straube, K., Gerstein, M. B., Butter, F. and Neugebauer, K. M. (2017). Dynamic RNA-protein interactions underlie the zebrafish maternal-to-zygotic transition . Genome Res. 27 , 1184-1194. 10.1101/gr.215954.116 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Dutagaci, B., Nawrocki, G., Goodluck, J., Ashkarran, A. A., Hoogstraten, C. G., Lapidus, L. J. and Feig, M. (2021). Charge-driven condensation of RNA and proteins suggests broad role of phase separation in cytoplasmic environments . eLife 10 , e64004. 10.7554/eLife.64004 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Eanes, W. F., Merritt, T. J. S., Flowers, J. M., Kumagai, S., Sezgin, E. and Zhu, C.-T. (2006). Flux control and excess capacity in the enzymes of glycolysis and their relationship to flight . Proc. Natl Acad. Sci. USA 103 , 19413-19418. 10.1073/pnas.0607095104 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Freeberg, M. A., Han, T., Moresco, J. J., Kong, A., Yang, Y.-C., Lu, Z., Yates, J. R. and Kim, J. K. (2013). Pervasive and dynamic protein binding sites of the mRNA transcriptome in Saccharomyces cerevisiae . Genome Biol. 14 , R13. 10.1186/gb-2013-14-2-r13 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Freeman Rosenzweig, E. S., Xu, B., Kuhn Cuellar, L., Martinez-Sanchez, A., Schaffer, M., Strauss, M., Cartwright, H. N., Ronceray, P., Plitzko, J. M., Förster, F.et al. (2017). The eukaryotic CO 2 -concentrating organelle is liquid-like and exhibits dynamic reorganization . Cell 171 , 148-162.e19. 10.1016/j.cell.2017.08.008 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Frottin, F., Schueder, F., Tiwary, S., Gupta, R., Körner, R., Schlichthaerle, T., Cox, J., Jungmann, R., Hartl, F. U. and Hipp, M. S. (2019). The nucleolus functions as a phase-separated protein quality control compartment . Science 365 , 342-347. 10.1126/science.aaw9157 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Fuller, G. G., Han, T., Freeberg, M. A., Moresco, J. J., Ghanbari Niaki, A., Roach, N. P., Yates, J. R., Myong, S. and Kim, J. K. (2020). RNA promotes phase separation of glycolysis enzymes into yeast G bodies in hypoxia . eLife 9 , e48480. 10.7554/eLife.48480 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Garcia-Jove Navarro, M.,, Kashida, S., Chouaib, R., Souquere, S., Pierron, G., Weil, D. and Gueroui, Z. (2019). RNA is a critical element for the sizing and the composition of phase-separated RNA-protein condensates . Nat. Commun. 10 , 3230. 10.1038/s41467-019-11241-6 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Giegé, P., Heazlewood, J. L., Roessner-Tunali, U., Millar, A. H., Fernie, A. R., Leaver, C. J. and Sweetlove, L. J. (2003). Enzymes of glycolysis are functionally associated with the mitochondrion in Arabidopsis cells . Plant Cell 15 , 2140-2151. 10.1105/tpc.012500 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Görlach, A.,, Dimova, E. Y., Petry, A., Martínez-Ruiz, A., Hernansanz-Agustín, P., Rolo, A. P., Palmeira, C. M. and Kietzmann, T. (2015). Reactive oxygen species, nutrition, hypoxia and diseases: Problems solved? Redox Biol. 6 , 372-385. 10.1016/j.redox.2015.08.016 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Graham, J. W. A., Williams, T. C. R., Morgan, M., Fernie, A. R., Ratcliffe, R. G. and Sweetlove, L. J. (2007). Glycolytic enzymes associate dynamically with mitochondria in response to respiratory demand and support substrate channeling . Plant Cell 19 , 3723-3738. 10.1105/tpc.107.053371 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Grignaschi, E., Cereghetti, G., Grigolato, F., Kopp, M. R. G., Caimi, S., Faltova, L., Saad, S., Peter, M. and Arosio, P. (2018). A hydrophobic low-complexity region regulates aggregation of the yeast pyruvate kinase Cdc19 into amyloid-like aggregates in vitro . J. Biol. Chem. 293 , 11424-11432. 10.1074/jbc.RA117.001628 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Haanstra, J. R., González-Marcano, E. B., Gualdrón-López, M. and Michels, P. A. M. (2016). Biogenesis, maintenance and dynamics of glycosomes in trypanosomatid parasites . Biochimica Biophysica. Acta 1863 , 1038-1048. 10.1016/j.bbamcr.2015.09.015 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Huang, R., Han, M., Meng, L. and Chen, X. (2018). Transcriptome-wide discovery of coding and noncoding RNA-binding proteins . Proc. Natl Acad. Sci. USA 115 , E3879-E3887. 10.1073/pnas.1718406115 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Hubstenberger, A., Courel, M., Bénard, M., Souquere, S., Ernoult-Lange, M., Chouaib, R., Yi, Z., Morlot, J.-B., Munier, A., Fradet, M.et al. (2017). P-Body purification reveals the condensation of repressed mRNA regulons . Mol. Cell 68 , 144-157. 10.1016/j.molcel.2017.09.003 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Huh, W.-K., Falvo, J. V., Gerke, L. C., Carroll, A. S., Howson, R. W., Weissman, J. S. and O'shea, E. K. (2003). Global analysis of protein localization in budding yeast . Nature 425 , 686-691. 10.1038/nature02026 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Hyman, A. A., Weber, C. A. and Jülicher, F. (2014). Liquid-liquid phase separation in biology . Annu. Rev. Cell Dev. Biol. 30 , 39-58. 10.1146/annurev-cellbio-100913-013325 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Jain, A. and Vale, R. D. (2017). RNA phase transitions in repeat expansion disorders . Nature 546 , 243-247. 10.1038/nature22386 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Jain, S., Wheeler, J. R., Walters, R. W., Agrawal, A., Barsic, A. and Parker, R. (2016). ATPase-modulated stress granules contain a diverse proteome and substructure . Cell 164 , 487-498. 10.1016/j.cell.2015.12.038 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Jang, S., Nelson, J. C., Bend, E. G., Rodríguez-Laureano, L., Tueros, F. G., Cartagenova, L., Underwood, K., Jorgensen, E. M. and Colón-Ramos, D. A. (2016). Glycolytic enzymes localize to synapses under energy stress to support synaptic function . Neuron 90 , 278-291. 10.1016/j.neuron.2016.03.011 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Jang, S., Xuan, Z., Lagoy, R. C., Jawerth, L. M., Gonzalez, I. J., Singh, M., Prashad, S., Kim, H. S., Patel, A., Albrecht, D. R.et al. (2021). Phosphofructokinase relocalizes into subcellular compartments with liquid-like properties in vivo . Biophys. J. 120 , 1170-1186. 10.1016/j.bpj.2020.08.002 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Jin, M., Fuller, G. G., Han, T., Yao, Y., Alessi, A. F., Freeberg, M. A., Roach, N. P., Moresco, J. J., Karnovsky, A., Baba, M.et al. (2017). Glycolytic enzymes coalesce in G bodies under hypoxic stress . Cell Reports 20 , 895-908. 10.1016/j.celrep.2017.06.082 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Khong, A., Matheny, T., Jain, S., Mitchell, S. F., Wheeler, J. R. and Parker, R. (2017). The stress granule transcriptome reveals principles of mRNA accumulation in stress granules . Mol. Cell 68 , 808-820.e5. 10.1016/j.molcel.2017.10.015 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Kleinschmidt, A. K., Moss, J. and Lane, D. M. (1969). Acetyl coenzyme A carboxylase: filamentous nature of the animal enzymes . Science 166 , 1276-1278. 10.1126/science.166.3910.1276 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Kohnhorst, C. L., Kyoung, M., Jeon, M., Schmitt, D. L., Kennedy, E. L., Ramirez, J., Bracey, S. M., Luu, B. T., Russell, S. J. and An, S. (2017). Identification of a multienzyme complex for glucose metabolism in living cells . J. Biol. Chem. 292 , 9191-9203. 10.1074/jbc.M117.783050 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Kojima, T. and Takayama, S. (2018). Membraneless compartmentalization facilitates enzymatic cascade reactions and reduces substrate inhibition . ACS Appl. Mater. Interfaces 10 , 32782-32791. 10.1021/acsami.8b07573 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Kroschwald, S., Maharana, S., Mateju, D., Malinovska, L., Nüske, E., Poser, I., Richter, D. and Alberti, S. (2015). Promiscuous interactions and protein disaggregases determine the material state of stress-inducible RNP granules . eLife 4 , e06807. 10.7554/eLife.06807 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Langdon, E. M., Qiu, Y., Ghanbari Niaki, A., Mclaughlin, G. A., Weidmann, C. A., Gerbich, T. M., Smith, J. A., Crutchley, J. M., Termini, C. M., Weeks, K. M.et al. (2018). mRNA structure determines specificity of a polyQ-driven phase separation . Science 360 , 922-927. 10.1126/science.aar7432 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Lange, S., Pinotsis, N., Agarkova, I. and Ehler, E. (2020). The M-band: the underestimated part of the sarcomere . Biochim. Biophys. Acta 1867 , 118440. 10.1016/j.bbamcr.2019.02.003 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Locasale, J. W. (2018). New concepts in feedback regulation of glucose metabolism . Curr. Opin. Syst. Biol. 8 , 32-38. 10.1016/j.coisb.2017.11.005 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Mateju, D., Franzmann, T. M., Patel, A., Kopach, A., Boczek, E. E., Maharana, S., Lee, H. O., Carra, S., Hyman, A. A. and Alberti, S. (2017). An aberrant phase transition of stress granules triggered by misfolded protein and prevented by chaperone function . EMBO J. 36 , 1669-1687. 10.15252/embj.201695957 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Matia-González, A. M., Laing, E. E. and Gerber, A. P. (2015). Conserved mRNA-binding proteomes in eukaryotic organisms . Nat. Struct. Mol. Biol. 22 , 1027-1033. 10.1038/nsmb.3128 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Menard, L., Maughan, D. and Vigoreaux, J. (2014). The structural and functional coordination of glycolytic enzymes in muscle: Evidence of a metabolon? Biology 3 , 623-644. 10.3390/biology3030623 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Merritt, T., Sezgin, E., Zhu, C.-T. and Eanes, W. F. (2006). Triglyceride pools, flight and activity variation at the Gpdh locus in Drosophila melanogaster . Genetics 172 , 293-304. 10.1534/genetics.105.047035 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Michels, P. A. M., Moyersoen, J., Krazy, H., Galland, N., Herman, M. and Hannaert, V. (2005). Peroxisomes, glyoxysomes and glycosomes (Review) . Mol. Membr. Biol. 22 , 133-145. 10.1080/09687860400024186 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Michels, P. A. M., Villafraz, O., Pineda, E., Alencar, M. B., Cáceres, A. J., Silber, A. M. and Bringaud, F. (2021). Carbohydrate metabolism in trypanosomatids: new insights revealing novel complexity, diversity and species-unique features . Exp. Parasitol. 224 , 108102. 10.1016/j.exppara.2021.108102 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Miura, N., Shinohara, M., Tatsukami, Y., Sato, Y., Morisaka, H., Kuroda, K. and Ueda, M. (2013). Spatial reorganization of Saccharomyces cerevisiae enolase to alter carbon metabolism under hypoxia . Eukaryot. Cell 12 , 1106-1119. 10.1128/EC.00093-13 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Morgenstern, M., Stiller, S. B., Lübbert, P., Peikert, C. D., Dannenmaier, S., Drepper, F., Weill, U., Höß, P., Feuerstein, R., Gebert, M.et al. (2017). Definition of a high-confidence mitochondrial proteome at quantitative scale . Cell Reports 19 , 2836-2852. 10.1016/j.celrep.2017.06.014 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Murakami, T., Qamar, S., Lin, J. Q., Schierle, G. S. K., Rees, E., Miyashita, A., Costa, A. R., Dodd, R. B., Chan, F. T. S., Michel, C. H.et al. (2015). ALS/FTD mutation-induced phase transition of FUS liquid droplets and reversible hydrogels into irreversible hydrogels impairs RNP granule function . Neuron 88 , 678-690. 10.1016/j.neuron.2015.10.030 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Noree, C., Begovich, K., Samilo, D., Broyer, R., Monfort, E. and Blanchoin, L. (2019). A quantitative screen for metabolic enzyme structures reveals patterns of assembly across the yeast metabolic network . Mol. Biol. Cell 30 , 2721-2736. 10.1091/mbc.E19-04-0224 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Pareek, V., Tian, H., Winograd, N. and Benkovic, S. J. (2020). Metabolomics and mass spectrometry imaging reveal channeled de novo purine synthesis in cells . Science 368 , 283-290. 10.1126/science.aaz6465 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Park, C. K. and Horton, N. C. (2019). Structures, functions, and mechanisms of filament forming enzymes: a renaissance of enzyme filamentation . Biophys. Rev. 11 , 927-994. 10.1007/s12551-019-00602-6 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Patel, A., Lee, H. O., Jawerth, L., Maharana, S., Jahnel, M., Hein, M. Y., Stoynov, S., Mahamid, J., Saha, S., Franzmann, T. M.et al. (2015). A liquid-to-solid phase transition of the ALS protein FUS accelerated by disease mutation . Cell 162 , 1066-1077. 10.1016/j.cell.2015.07.047 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Petrova, V., Annicchiarico-Petruzzelli, M., Melino, G. and Amelio, I. (2018). The hypoxic tumour microenvironment . Oncogenesis 7 , 10. 10.1038/s41389-017-0011-9 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Potter, M., Newport, E. and Morton, K. J. (2016). The Warburg effect: 80 years on . Biochem. Soc. Trans. 44 , 1499-1505. 10.1042/BST20160094 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Protter, D. S. W., Rao, B. S., Van Treeck, B., Lin, Y., Mizoue, L., Rosen, M. K. and Parker, R. (2018). Intrinsically disordered regions can contribute promiscuous interactions to RNP granule assembly . Cell Reports 22 , 1401-1412. 10.1016/j.celrep.2018.01.036 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Puchulu-Campenella, E., Chu, H., Anstee, D. J., Galan, J. A., Tao, W. A. and Low, P. S. (2013). Identification of the components of a glycolytic enzyme metabolon on the human red blood cell membrane . J. Biol. Chem. 288 , 848-858. 10.1074/jbc.M112.428573 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Putnam, A., Cassani, M., Smith, J. and Seydoux, G. (2019). A gel phase promotes condensation of liquid P granules in Caenorhabditis elegans embryos . Nat. Struct. Mol. Biol. 26 , 220-226. 10.1038/s41594-019-0193-2 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Quiñones, W., Acosta, H., Gonçalves, C. S., Motta, M. C. M., Gualdrón-López, M. and Michels, P. A. M. (2020). Structure, properties, and function of glycosomes in Trypanosoma cruzi . Front. Cell Infect. Microbiol. 10 , 25. 10.3389/fcimb.2020.00025 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Rothe, S., Prakash, A. and Tyedmers, J. (2018). The insoluble protein deposit (IPOD) in yeast . Front. Mol. Neurosci. 11 , 237. 10.3389/fnmol.2018.00237 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Saad, S., Cereghetti, G., Feng, Y., Picotti, P., Peter, M. and Dechant, R. (2017). Reversible protein aggregation is a protective mechanism to ensure cell cycle restart after stress . Nat. Cell Biol. 19 , 1202-1213. 10.1038/ncb3600 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Schöneberg, T., Kloos, M., Brüser, A., Kirchberger, J. and Sträter, N. (2013). N. Structure and allosteric regulation of eukaryotic 6-phosphofructokinases . Biol. Chem. 394 , 977-993. 10.1515/hsz-2013-0130 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Shchepachev, V., Bresson, S., Spanos, C., Petfalski, E., Fischer, L., Rappsilber, J. and Tollervey, D. (2019). Defining the RNA interactome by total RNA-associated protein purification . Mol. Syst. Biol. 15 , e8689. 10.15252/msb.20188689 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Shen, Q.-J., Kassim, H., Huang, Y., Li, H., Zhang, J., Li, G., Wang, P.-Y., Yan, J., Ye, F. and Liu, J.-L. (2016). Filamentation of metabolic enzymes in Saccharomyces cerevisiae . J. Genet. Genomics 43 , 393-404. 10.1016/j.jgg.2016.03.008 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Srere, P. A. (1987). Complexes of sequential metabolic enzymes . Annu. Rev. Biochem. 56 , 89-124. 10.1146/annurev.bi.56.070187.000513 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Stoddard, P. R., Lynch, E. M., Farrell, D. P., Dosey, A. M., Dimaio, F., Williams, T. A., Kollman, J. M., Murray, A. W. and Garner, E. C. (2020). Polymerization in the actin ATPase clan regulates hexokinase activity in yeast . Science 367 , 1039-1042. 10.1126/science.aay5359 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Sträter, N., Marek, S., Kuettner, E. B., Kloos, M., Keim, A., Brüser, A., Kirchberger, J. and Schöneberg, T. (2011). Molecular architecture and structural basis of allosteric regulation of eukaryotic phosphofructokinases . FASEB J. 25 , 89-98. 10.1096/fj.10-163865 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Sullivan, D. T., Macintyre, R., Fuda, N., Fiori, J., Barrilla, J. and Ramizel, L. (2003). Analysis of glycolytic enzyme co-localization in Drosophila flight muscle . J. Exp. Biol. 206 , 2031-2038. 10.1242/jeb.00367 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Sweetlove, L. J. and Fernie, A. R. (2018). The role of dynamic enzyme assemblies and substrate channeling in metabolic regulation . Nat. Commun. 9 , 2136. 10.1038/s41467-018-04543-8 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Sysoev, V. O., Fischer, B., Frese, C. K., Gupta, I., Krijgsveld, J., Hentze, M. W., Castello, A. and Ephrussi, A. (2016). Global changes of the RNA-bound proteome during the maternal-to-zygotic transition in Drosophila . Nat. Commun. 7 , 12128. 10.1038/ncomms12128 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Trcek, T., Grosch, M., York, A., Shroff, H., Lionnet, T. and Lehmann, R. (2015). Drosophila germ granules are structured and contain homotypic mRNA clusters . Nat. Commun. 6 , 7962. 10.1038/ncomms8962 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Trcek, T., Douglas, T. E., Grosch, M., Yin, Y., Eagle, W. V. I., Gavis, E. R., Shroff, H., Rothenberg, E. and Lehmann, R. (2020). Sequence-independent self-assembly of germ granule mRNAs into homotypic clusters . Mol. Cell 78 , 941-950. 10.1016/j.molcel.2020.05.008 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Van Treeck, B., Protter, D. S. W., Matheny, T., Khong, A., Link, C. D. and Parker, R. (2018). RNA self-assembly contributes to stress granule formation and defining the stress granule transcriptome . Proc. Natl. Acad. Sci. USA 115 , 2734-2739. 10.1073/pnas.1800038115 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Waingeh, V. F., Gustafson, C. D., Kozliak, E. I., Lowe, S. L., Knull, H. R. and Thomasson, K. A. (2006). Glycolytic enzyme interactions with yeast and skeletal muscle F-Actin . Biophys. J. 90 , 1371-1384. 10.1529/biophysj.105.070052 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Wallace, E. W. J., Kear-Scott, J. L., Pilipenko, E. V., Schwartz, M. H., Laskowski, P. R., Rojek, A. E., Katanski, C. D., Riback, J. A., Dion, M. F., Franks, A. M.et al. (2015). Reversible, specific, active aggregates of endogenous proteins assemble upon heat stress . Cell 162 , 1286-1298. 10.1016/j.cell.2015.08.041 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Walters, R. W., Muhlrad, D., Garcia, J. and Parker, R. (2015). Differential effects of Ydj1 and Sis1 on Hsp70-mediated clearance of stress granules in Saccharomyces cerevisiae . RNA 21 , 1660-1671. 10.1261/rna.053116.115 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Webb, B. A., Dosey, A. M., Wittmann, T., Kollman, J. M. and Barber, D. L. (2017). The glycolytic enzyme phosphofructokinase-1 assembles into filaments . J. Cell Biol. 216 , 2305-2313. 10.1083/jcb.201701084 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Wojtas, K., Slepecky, N., Von Kalm, L. and Sullivan, D. (1997). Flight muscle function in Drosophila requires colocalization of glycolytic enzymes . Mol. Biol. Cell 8 , 1665-1675. 10.1091/mbc.8.9.1665 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Wunder, T., Cheng, S. L. H., Lai, S.-K., Li, H.-Y. and Mueller-Cajar, O. (2018). The phase separation underlying the pyrenoid-based microalgal Rubisco supercharger . Nat. Commun. 9 , 5076. 10.1038/s41467-018-07624-w [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Yoshimura, Y., Hirayama, R., Miura, N., Utsumi, R., Kuroda, K., Ueda, M. and Kataoka, M. (2021). Small-scale hypoxic cultures for monitoring the spatial reorganization of glycolytic enzymes in Saccharomyces cerevisiae . Cell Biol. Int. 45 , 1776-1783. 10.1002/cbin.11617 [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Zhang, H., Elbaum-Garfinkle, S., Langdon, E. M., Taylor, N., Occhipinti, P., Bridges, A. A., Brangwynne, C. P. and Gladfelter, A. S. (2015). RNA controls PolyQ protein phase transitions . Mol. Cell 60 , 220-230. 10.1016/j.molcel.2015.09.017 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
  • Zhang, Y., Sampathkumar, A., Kerber, S. M.-L., Swart, C., Hille, C., Seerangan, K., Graf, A., Sweetlove, L. and Fernie, A. R. (2020). A moonlighting role for enzymes of glycolysis in the co-localization of mitochondria and chloroplasts . Nat. Commun. 11 , 4509. 10.1038/s41467-020-18234-w [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]

write a essay on glycolysis

Glycolysis n., plural: glycolyses [ɡlaɪˈkɒlɪsɪs] Definition: Degradation of simple sugar to pyruvic acid

Table of Contents

What is Glycolysis and Why is it Important?

Glycolysis is a metabolic pathway by which the 6- carbon molecule of glucose is broken down into a 3-C molecule called pyruvate in a series of complex oxidizing biochemical reactions. The byproduct of these reactions is the release of free energy, which is stored in the high-energy phosphate bonds of ATP and other reducing equivalents, such as NADH/H + that are further used to produce more ATP in the mitochondria.

ATP is famously known as the energy currency of the cell . ATP is a high-energy molecule that fuels most of the cellular energy requirements. This is how the carbohydrates we consume in our diet are utilized inside our bodies to generate energy.

Let’s answer this common question: What is the purpose of glycolysis?

Glycolysis is an extremely important pathway that converts glucose to pyruvate. This conversion is necessary for the production of ATP without which the cells cannot survive. Glycolysis occurs in the cytoplasm of all cells. It can occur in either the presence or absence of oxygen. When it occurs in the presence of oxygen it is called aerobic glycolysis . When it occurs in the absence of oxygen it is called anaerobic glycolysis . Its presence in a wide variety of organisms suggests that it is a primitive pathway that has been the basis of the derivation of energy for a long time.

Now, let’s answer some basic questions about glycolysis:

Question: What does glycolysis produce? Answer: Glycolysis products are 2 pyruvate, 2 NADH + 2H + and 2ATP molecules The net reaction of glycolysis is:

Glucose + 2 NAD + + 2 ADP + 2 P i → 2 pyruvates + 2 NADH + 2 H + + 2 ATP

Question: How much NADH is produced by glycolysis? Answer: 2 NADH molecules are produced by a single molecule of glucose in the glycolytic reaction.

Question: Where does glycolysis occur? Answer: The location of glycolysis is the cytoplasm of the cell.

Question: What is the meaning of EMP? Answer: EMP is an abbreviation of the Embden-Meyerhof-Parnas pathway . EMP pathway is just another name for the glycolysis pathway.

Question: Why is ATP required for glycolysis? Answer: ATP is required in the initial few steps of glycolysis in the preparatory phase so that the 6-C glucose can be broken down into two 3-C compounds.

Question: Does glycolysis require oxygen? Answer: Glycolysis does not necessarily require oxygen. It can occur in the absence of oxygen as well.

Biology definition: Glycolysis is a series of reactions happening in the cytosol that results in the conversion of a monosaccharide, often glucose , into pyruvate , and the concomitant production of a relatively small amount of high-energy biomolecules, such as ATP . It is the initial metabolic pathway of cellular respiration . Cellular respiration is a series of metabolic processes wherein the biochemical energy is harvested from an organic substance (e.g. glucose ) and stored in energy carriers (e.g. ATP) for use in energy-requiring activities of the cell . The major steps or processes of cellular respiration are (1) glycolysis , (2) Krebs cycle , and (3) oxidative phosphorylation .

The most common and well-known type of glycolysis is the Embden-Meyerhof-Parnas pathway , which was first described by Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas. Other alternative pathways are exemplified by the Entner-Doudoroff pathway and the Pentose phosphate pathway . In the Embden-Meyerhof-Parnas pathway, glycolysis is comprised of two phases: (1) the energy-investment phase (where ATP is consumed) and (2) the energy-payoff phase (where ATP is produced). The splitting of sugar during the energy-investment phase characterizes glycolysis in this regard since glucose is split into two triose phosphates : glyceraldehyde phosphate and dihydroxyacetone phosphate . The glyceraldehyde phosphate proceeds to the energy-payoff phase whereas its isomer, dihydroxyacetone phosphate, has to be converted to glyceraldehyde phosphate (via isomerase) before it can p.

Etymology: Greek “glykys”, meaning “sweet” (referring to sugar) and “Iyein”, meaning “to loosen”. Related form: glycolytic (adj.) See also:

  • cellular respiration

What is the Embden–Meyerhof–Parnas (EMP) pathway? It is the most common type of glycolytic pathway which was discovered by scientists — Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas . The discovery of the pathway took almost 100 years to fully unravel. The discovery of the glycolysis mechanism was originally seceded from the curiosity to understand the fermentation process, so that better wines could be made. The study of the biochemistry of glycolysis started with the experiments of the French scientist Louis Pasteur on yeast in the year 1850. He observed that the consumption of glucose decreased significantly under aerobic conditions as compared to consumption under anaerobic conditions, this effect is known as the Pasteur effect . Later, many different scientists contributed to elucidating the glycolytic pathway. Gustav Embden, by 1930 laid down all the bits and pieces of different steps together and proposed a detailed pathway.

Sequence of Reactions

Now let’s see what happens in the process of glycolysis.

Summary of reactions

The process of glycolysis can be divided into different phases. There are a total of 9 steps of glycolysis ,  each of which is described below in detail.

Glycolysis equation is as follows:

Glucose + 2 NAD + + 2 ADP + 2 P i → 2 pyruvates + 2 NADH + 2 H +  + 2 ATP
  • Stage of phosphorylation : Net energy is spent in this phase.
  • Stage of splitting : 6-C compound splits into two 3-C compounds in this phase.
  • Payoff phase : This phase is responsible for the generation of net ATP and NADH + H +

Summary of glycolysis reactions

Preparatory phase: Stage of Phosphorylation

Step-1: glucose ➔ glucose-6-phosphate (g6p).

Glucose is phosphorylated to form Glucose-6-phosphate (G6P) by the enzyme glucokinase or hexokinase . This is an energy-requiring step, and 1 ATP is consumed for the phosphorylation of one glucose molecule. It is the first irreversible step of glycolysis . Hence, it is also known as the flux generating step . This step is important as the phosphorylated glucose molecule is trapped by the cell for further metabolism . The trapping occurs because the cell membrane is not permeable to G6P. The G6P can enter different metabolic pathways, namely Glycogen synthesis, HMP pathway, Uronic acid pathway, and Glycolysis. This article mainly focuses on the utilization of Glucose-6-phosphate in the glycolytic pathway.

Step-2: G6P ➔ Fructose-6-phosphate (F6P)

After this step, the glucose-6-phosphate is converted into fructose-6-phosphate (F6P) by the enzyme phosphohexose isomerase .

Step-3: F6P ➔ Fructose-1,6-bisphosphate (F1,6BP)

Now, the fructose-6-phosphate is once again phosphorylated by the enzyme phosphofructokinase 1 (PFK-1) to form fructose-1,6-bisphosphate (F1,6BP). This is also an energy-requiring step and consumes 1 ATP. Mg ++ is a cofactor of the enzyme PFK-1. PFK-1 is also the rate-limiting enzyme of glycolysis. This step is the second irreversible step of glycolysis . It is also the first committed step of glycolysis as F1,6BP cannot escape glycolysis now. It is also known as the bottleneck of the pathway .

Preparatory phase: Stage of Splitting

Step 4: f1,6bp ➔ dihydroxyacetone phosphate (dhap) + glyceraldehyde-3-phosphate (g3p).

F1,6BP is a 6-C compound which in this step splits into two 3-C compounds, namely, dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P) with the help of the enzyme aldolase . Phospho-triose isomerase can convert DHAP into G3P and vice versa. G3P participates in the further reactions of glycolysis.

Pay-off phase

In this phase of glycolysis, energy is yielded in the form of ATP, and reducing equivalents are generated.

Step 5: G3P ➔ 1,3 Bisphosphoglycerate (1,3BPG)

G3P molecule is converted into 1,3 Bisphosphoglycerate (1,3BPG) by the enzyme Glyceraldehyde-3-phosphate dehydrogenas e. During this step, one inorganic phosphate (P i ) is utilized and one NAD + gets reduced to NADH + H +

Step 6: 1,3BPG ➔ 3-Phosphoglycerate (3PG)

1,3 BPG is a high-energy compound, which gets converted to 3-Phosphoglycerate (3PG) by the enzyme 1,3BPG kinase . This enzyme is the only reversible kinase of the entire glycolytic pathway. In this step, substrate-level phosphorylation occurs, where ADP is converted into ATP.

Step 7: 3PG ➔ 2-phosphoglycerate (2PG)

3PG is converted into 2-phosphoglycerate (2PG) by the enzyme phosphoglycerate mutase .

Step 8: 2PG ➔ phosphoenolpyruvate (PEP)

2PG is converted into phosphoenolpyruvate (PEP) by the enzyme enolase . During this step, a water molecule is released.

Step 9: PEP ➔ pyruvate

PEP is a high-energy compound that is converted into pyruvate by the enzyme pyruvate kinase . Pyruvate is the end product of glycolysis. Second substrate-level phosphorylation occurs during this step yielding another ATP molecule.

The overall steps OR the model of glycolysis are represented by the glycolysis cycle which can be seen in this figure.

Diagram of glycolysis cycle by Baydaa Hassan

Energetics of glycolysis

The energetics of the glycolysis tells us how much ATP is produced in glycolysis. The energy produced by glycolysis is different under aerobic and anaerobic conditions. This is so because, under aerobic conditions, there is an extra generation of 2 NADH molecules that are further oxidized inside the mitochondrion to produce ATP. This oxidation of NADH within the mitochondria is responsible for the generation of 2.5 ATP molecules per NADH molecule . However, under anaerobic conditions, there is no net generation of NADH. The differences in the overall energetics of glycolysis under aerobic and anaerobic conditions are summarized in Table 1.

Energetics of Glycolytic reaction

Biochemical logic

In the pathway of glycolysis, there are multiple regulatory steps such as Step-1 and Step-3. These different regulatory checkpoints in the pathway indicate that the intermediates of glycolysis are links to other metabolic pathways. For example, after Step-1 of glycolysis, glucose-6-phosphate can leave the glycolysis and enter the HMP pathway , glycogen synthesis , or uronic acid pathway . Similarly, after step-3, DHAP can be diverted from glycolysis by conversion into G3P. Then, G3P can enter fatty acid synthesis, or conversely when lipolysis occurs, the glycerol released can be converted into DHAP that can enter the glycolytic pathway.

Free energy changes

The free energy change is represented by ΔG. The ΔG can be calculated for each step by the equation ΔG = ΔG°’ + RTln Q , where Q represents the reaction quotient . Three steps of glycolysis are not in equilibrium as they are the irreversible steps of glycolysis . This is represented by the large free energy change of that step.

Here are the various regulatory mechanisms involved in glycolysis.

Biological mechanisms by which enzymes are regulated

There are different sites and steps at which glycolysis is regulated by various mechanisms. The regulation of glycolysis mainly happens because of the alteration of the enzymes. The various mechanisms by which the enzymes are altered are:

  • Allosteric modification – the allosteric modification is such that the substrates mostly favor the enzyme activity and products mostly inhibit the enzyme activity. So, for example, when there are more substrates , the net effect will result in the stimulation of the enzyme’s activity and favor product formation. The reverse is true when product concentration is more than the substrate.
  • Gene expression
  • Protein-protein interaction
  • Post-translational modification
  • Localization

Regulation by insulin in animals

Changing insulin and glucagon levels in the body according to the fed-fast cycle is responsible for covalent modification of the enzymes.

  • When blood glucose levels are low , it stimulates the pancreatic α-cells to secrete glucagon and adrenal glands to secrete epinephrine. The Glucagon/Epinephrine in the liver phosphorylates the enzymes of glycolysis by activating protein kinase A. The enzymes of glycolysis are inactive when they are in a phosphorylated state. Hence, during a fasting state, when insulin is low and glucagon is high in the body, the enzymes of glycolysis are inactive.
  • When blood glucose level is high , it stimulates pancreatic β-cells to secrete insulin. Insulin activates the enzyme phosphatase which converts the phosphorylated/active enzymes into dephosphorylated/inactive enzymes. Insulin also reduces the activity of cAMP-dependent protein kinase . Hence, under the influence of high insulin, the enzymes of glycolysis are active.

Regulation of the rate-limiting enzymes

There are four regulatory enzymes:

  • Glucokinase
  • Phosphofructokinase
  • Pyruvate kinase

Glucokinase/Hexokinase

These two enzymes catalyze step-1 of glycolysis. The enzyme hexokinase is ubiquitous and is present in every cell whereas glucokinase is only present in certain specific cells of the liver and pancreas. Although these two enzymes catalyze the same reactions, there are certain differences between the properties of these two enzymes. The important differences between hexokinase and glucokinase enzymes are presented in Table 2 below.

In pancreatic cells, glucokinase is active when there is abundant blood glucose. The glycolysis in the pancreatic cells produces ATP which closes the ATP-sensitive potassium channels (K + channels). Due to the closure of K + channels, depolarization of the cell occurs. This leads to a massive influx of calcium. Calcium is responsible for the secretion of insulin. The mechanism of insulin release can be seen in Figure 4. The insulin as previously discussed influences the activity of the glycolytic enzymes.

mechanism of insulin release - diagram by CM Girgis

Phosphofructokinase-1 (PFK-1):

Phosphofructokinase is a very important regulatory step as it is an irreversible step of glycolysis. It has many allosteric effectors, a summary of which can be seen in Table 3 . When the insulin/glucagon ratio in the blood is low, the phosphorylation/inactivation of the second phosphofructokinase occurs. This converts fructose-6-phosphate (F6P) into fructose-2,6-bisphosphate (F2,6BP). With the phosphorylation, another domain of the same enzyme F2,6BP gets activated, which converts F2,6BP back into F6P. Since F2,6BP is a very potent stimulator of the enzyme PFK-1, under low insulin/glucagon ratio, PFK-1 is inactive, and under high insulin/glucagon ratio PFK-1 is active.

When the cell energy charge is low, AMP is high. AMP is an important stimulator of PFK-1.

Pyruvate Kinase:

Pyruvate kinase that is in the liver is different from pyruvate kinase in muscle. In the liver, the pyruvate kinase enzyme is phosphorylated/deactivated by the epinephrine/glucagon induced protein kinase A . However, the muscle pyruvate kinase is unaffected by the epinephrine/glucagon induced protein kinase A . Hence, in a fasting state, glycolysis stops in the liver whereas it can continue to occur in the muscle.

Post-glycolysis Processes

When glycolysis occurs, NAD + of the cell is used up. For the glycolysis to continue there must be the regeneration of NAD + within the cell. There are many ways by which organisms regenerate their NAD + .

Anoxic regeneration of NAD +

NAD + regeneration, when occurs under anaerobic conditions, is called anoxic regeneration . When NAD +  regeneration occurs anaerobically, it is much faster when compared to aerobic regeneration of NAD + .

Lactic acid fermentation

Aerobic regeneration of NAD + , and disposal of pyruvate

The site of glycolysis is different from the site of oxidative phosphorylation . The ATP made during glycolysis is generated by the mitochondria. Under the aerobic condition, the NADH is transported into the mitochondria via the malate aspartate shuttle and glycerol phosphate shuttle. In the inner mitochondrial membrane, there is a sequence of electron acceptors arranged in increasing order of redox potential. The electrons are then transferred from NADH to this electron transport chain and ultimately to oxygen and thus NAD +  is regenerated. The energy released during the process is used to generate a proton gradient across the inner mitochondrial membrane. This proton gradient ultimately drives the ATP synthesis. The aerobic regeneration of NAD +  is a much more energy-efficient process than anaerobic regeneration.

The pyruvate under aerobic conditions undergoes a series of complex biochemical reactions catalyzed by a complex of three different enzymes collectively called pyruvate dehydrogenase complex (PDC). The 3-C pyruvate is converted into CO 2 , NADH + H + , and a 2-C acetyl CoA. The Acetyl CoA then enters the TCA cycle.

Under anaerobic conditions, the pyruvate as previously discussed gets converted into lactate or ethanol.

Conversion of carbohydrates into fatty acids and cholesterol

The acetyl CoA produced in the mitochondria from pyruvate is an important link between carbohydrate metabolism, fatty acid synthesis, and cholesterol synthesis . For either fatty acid synthesis or cholesterol synthesis, the acetyl CoA needs to be transported to cytosol. Since the inner mitochondrial membrane is impermeable to acetyl CoA, it uses oxaloacetate as a transporter .

Mitochondrial oxaloacetate combines with acetyl CoA to form citrate . The citrate then crosses the mitochondrial membrane to move to the cytosol. Here, citrate is cleaved by ATP-citrate lyase into acetyl CoA and oxaloacetate . The oxaloacetate inside the mitochondrion, btw, returns the acetyl CoA into the cytosol — see Figure 8. Once the acetyl CoA is in the cytosol it can either be carboxylated by acetyl CoA carboxylase enzyme to form malonyl CoA, which is the first intermediate required for fatty acid synthesis OR it can be combined with aceto-acetyl CoA to form HMG-CoA , which is the rate-limiting step of cholesterol synthesis.

Transport of Acetyl CoA from mitochondria to cytosol

Conversion of pyruvate into oxaloacetate for the citric acid cycle

After glycolysis, mitochondria handle further metabolism of pyruvate. It is oxidized by the PDC pyruvate dehydrogenase enzyme complex. The acetyl CoA thus produced enters the TCA cycle for further metabolism. The first step of the TCA cycle is the interaction between oxaloacetate and acetyl CoA to form citrate. As noted in the above figure, pyruvate can be actively converted into oxaloacetate with the help of the pyruvate carboxylase enzyme. This is an anapleurotic reaction of the TCA cycle, which means that it is a filling-up reaction that helps in increasing the other intermediates of the TCA cycle as the cycle progresses. With the increase in the intermediates of the TCA cycle, the processing capability of acetyl CoA for metabolism also increases. The key steps of the TCA cycle can be seen in Figure 9.

Krebs cycle or TCA cycle

Intermediates For Other Pathways

As we already learned, a six-carbon sugar, such as glucose , is the ‘starting point’ of the glycolytic pathway. The ‘end point’ is the three-carbon molecule, pyruvate . The various products of the glycolytic pathway (referred to as glycolytic metabolites ) serve as important intermediates for other metabolic pathways:

  • Glucose 6-phosphate (G6P) (C 6 H 13 O 9 P), the first intermediate of the glycolytic pathway, may also be used as an intermediate of the Pentose Phosphate Pathway (PPP). As the name implies, this pathway produces NADPH and pentose phosphates (such as ribose 5-phosphate , which is essential in nucleotide or nucleic acid synthesis and erythrose 4-phosphate , which is for aromatic amino acid synthesis). G6P may also be stored as glycogen (such as in the liver and muscles of many animals) and as glycogen granules or intracellular starch in other organisms.
  • Fructose 6-phosphate (C 6 H 13 O 9 P), the second intermediate of glycolysis, can also serve as an intermediate of PPP and for starch synthesis (e.g., in chloroplasts ).
  • Glyceraldehyde 3-phosphate (G3P) (C 5 H 7 O 6 P) is a glycolytic intermediate that is formed after the hexose splits into two, and through the action of the enzyme triosephosphate isomerase , G3P may be reversibly interconverted into DHAP. Apart from glycolysis, G3P is an intermediate of gluconeogenesis and also of the Calvin Cycle of photosynthesis . In photosynthesis, two molecules of G3P may be rearranged and combined to form glucose, which, in turn, may be utilized or stored as a polysaccharide (e.g., starch). G3P also has a role in the biosynthesis of thiamine (vitamin B 1 )
  • Dihydroxyacetone phosphate (DHAP) (C 5 H 7 O 6 P), together with G3P, is formed after the splitting of the hexose sugar (as mentioned above). DHAP cannot enter the glycolytic pathway directly; it is first converted to G3P via the enzyme, triosephosphate isomerase . However, if not in the glycolytic pathway, DHAP enters other pathways. For instance, DHAP is used in glycogen metabolism or lipid biosynthesis. In plants, it is used in the Calvin cycle, particularly during the regeneration of RuBP (ribulose-1,5-bisphosphate).
  • 1,3-biphosphoglycerate (1,3BPG) (C 3 H 8 O 10 P 2 ) is the intermediate of glycolysis that is formed after the oxidation of G3P through the enzyme glyceraldehyde-3-phosphate dehydrogenase . In plants, 1,3BPG is used in the Calvin cycle, reducing it to produce G3P. In humans, about 20% of 1,3BPG produced would not go any further into the glycolytic pathway but take an alternate route, the Luebering-Rapoport pathway . In this pathway, 1,3BPG is converted into 2,3-bisphosphoglyceric acid (2,3BPG) through the action of the enzyme BPG mutase . 2,3BPG promotes the release of oxygen from the red blood cell to nearby tissues where oxygen seems more necessary.
  • 3-phosphoglycerate (3PG) (C 3 H 7 O 7 P) is an intermediate of glycolysis formed after dephosphorylating 1,3BPG. In glycolysis, 3GP is converted into 2-phosphoglycerate by relocating the lone phosphate group. In other pathways, particularly the Calvin cycle, 3-PGA is phosphorylated to form 1,3BPG via the enzyme phosphoglycerate kinase .
  • Phosphoenolpyruvate (PEP) (C 3 H 5 O 6 P) is an intermediate of glycolysis formed by converting 2-phosphoglycerate with the help of the enzyme enolase . In glycolysis, PEP loses the phosphate group for the final substrate-level phosphorylation and for the production of pyruvate (the final product of glycolysis) through the enzyme pyruvate kinase . In another pathway, PEP is used in the shikimate pathway to produce chorismate , which is an important intermediate in the biosynthesis of the amino acids phenylalanine , tryptophan , and tyrosine , various alkaloids, vitamin K, folate, and the plant hormone salicylic acid . In C 4 plants , PEP is a substrate in the C 4 carbon fixation , which is a pathway where carbon dioxide is first bound to PEP in the mesophyll cell to produce oxaloacetate. The latter is then shuttled to the bundle sheath cell where it will eventually be decarboxylated (release of carbon dioxide). The liberated carbon dioxide, in turn, is fixed via the C3 pathway . This mechanism helped C 4 plants, such as sugarcane, maize, sorghum, to minimize the potential energy loss from photorespiration .

glycolytic pathway

Glycolysis in Disease

Defects in the glycolytic pathway have been associated with certain diseases, such as diabetes, genetic disorders, and cancer.

Diabetes is a condition characterized by the inability to produce sufficient insulin. Insulin is a hormone that is crucial in maintaining the homeostatic level of glucose in the blood. Under normal conditions, the beta cells of the pancreas release an adequate amount of insulin when the blood glucose level is high. The role of insulin is to promote the uptake of glucose from the bloodstream by the cells of the body.

The inability to properly take up glucose by the cells could result in high amounts of glucose circulating in the blood . The condition wherein the blood glucose level is excessively high is referred to as hyperglycemia . Hyperglycemia is one of the symptoms of diabetes, which is a disease caused by insufficient insulin production (possibly due to a defective gene in the pancreatic beta cells involved in insulin production).

Genetic diseases

Dysfunctional genes associated with the production of enzymes involved in glycolysis could manifest as genetic disorders . Examples:

  • Pyruvate kinase deficiency is a metabolic disorder caused by a mutation in the PKLR gene. This condition would therefore affect glycolysis as there would be not enough pyruvate kinase to catalyze the release of phosphate from PEP.
  • Hyperinsulinemic hypoglycemia is a metabolic disorder due to a deficiency in glucokinase caused by a defective GCK gene in the pancreatic beta cells.
  • Glucose-6-phosphate isomerase deficiency is a deficiency in glucose-6-phosphate isomerase (enzyme in the reaction: Glucose 6-phosphate → Fructose 6-phosphate) caused by defective GPI gene in red blood cells.
  • Tarui’s disease is a deficiency in phosphofructokinase (enzyme in the reaction: β-D-fructose 6-phosphate → β-D-fructose 1,6-bisphosphate) caused by defective PFKL gene in the liver cell or by the PFKM gene in the muscle cell.
  • Glycogen storage disease type XII is a metabolic disorder due to a deficiency in fructose-bisphosphate aldolase production caused by a defective ALDOA gene in the muscle, liver, and red blood cells; aldolase A is an enzyme in the reaction: Fructose 1,6-bisphosphate → Dihydroxyacetone phosphate.
  • Triosephosphate isomerase deficiency , a deficiency in the triosephosphate isomerase , is caused by a defective TPI1 gene in the red blood cells. The enzyme catalyzes the reversible interconversion of G3P and DHAP.
  • GSD type X is a phosphoglycerate mutase deficiency resulting in myopathy. It is caused by a defective PGAM2 gene in the muscle. The enzyme phosphoglycerate mutase is an enzyme essential in catalyzing the reaction 1,3-Bisphosphoglycerate → 3-Phosphoglycerate.
  • Enolase deficiency , an autoimmune disorder due to the lack of sufficient enolase caused by a defective ENO1 gene in the red blood cells.
  • Pyruvate kinase deficiency , a deficiency in pyruvate kinase , is caused by a defective PKLR gene in the red blood cells and liver.
  • Baker-Winegrad disease , a deficiency in fructose bisphosphatase , is caused by a defective FBP1 gene in the liver.

Cancer cells are essentially cells; thus, the thought that sugar consumption could make cancer “grow” faster might have some basis. By way of glycolysis, glucose, for instance, is degraded so as to produce energy via substrate-level phosphorylation. According to studies, cancer cells tend to use sugar about 200 times more than normal cells. (Ratini, 2019) Because they are a growing mass of cells, their energy requirement would apparently be high. And thus, to fuel this demand, cancer cells may utilize the glycolytic pathway more profoundly than the normal cells. Nevertheless, this topic is still undergoing a thorough study and therefore needs scientific proof to reach a wider consensus.

Try to answer the quiz below to check what you have learned so far about glycolysis.

Choose the best answer. 

Send Your Results (Optional)

clock.png

Time is Up!

  • A. Hassan, Baydaa. (2019). glycolysis Embden–Meyerhof–Parnas (EMP) pathway. 10.13140/RG.2.2.36127.82089.
  • Protasoni, Margherita & Zeviani, Massimo. (2021). Mitochondrial Structure and Bioenergetics in Normal and Disease Conditions. International Journal of Molecular Sciences. 22. 586. 10.3390/ijms22020586.
  • Fernie, A. R., Carrari, F., & Sweetlove, L. J. (2004). Respiratory metabolism: glycolysis, the TCA cycle and mitochondrial electron transport. Current opinion in plant biology, 7(3), 254–261. https://doi.org/10.1016/j.pbi.2004.03.007
  • Granner, D. K., & Rodwell, V. W. (2006). Harper’s illustrated biochemistry (27th ed.). New York: Lange Medical Books/McGraw-Hill.
  • Rath, L. (2019, February 20). Cancer and Sugar: Is There a Link? WebMD; WebMD. https://www.webmd.com/cancer/features/cancer-sugar-link

©BiologyOnline.com. Content provided and moderated by Biology Online Editors.

Last updated on May 29th, 2023

You will also like...

write a essay on glycolysis

Plant Metabolism

write a essay on glycolysis

Protein Activity and Cellular Metabolism

write a essay on glycolysis

Cell Respiration

write a essay on glycolysis

ATP & ADP – Biological Energy

write a essay on glycolysis

Related Articles...

write a essay on glycolysis

No related articles found

Library homepage

  • school Campus Bookshelves
  • menu_book Bookshelves
  • perm_media Learning Objects
  • login Login
  • how_to_reg Request Instructor Account
  • hub Instructor Commons
  • Download Page (PDF)
  • Download Full Book (PDF)
  • Periodic Table
  • Physics Constants
  • Scientific Calculator
  • Reference & Cite
  • Tools expand_more
  • Readability

selected template will load here

This action is not available.

Chemistry LibreTexts

9.1: Glycolysis - Reaction and Regulation

  • Last updated
  • Save as PDF
  • Page ID 166215

Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. Nearly all living organisms carry out glycolysis as part of their metabolism. The process does not use oxygen and is therefore anaerobic. Glycolysis takes place in the cytoplasm of both prokaryotic and eukaryotic cells. Glucose enters heterotrophic cells in two ways. One method is through secondary active transport in which the transport takes place against the glucose concentration gradient. The other mechanism uses a group of integral proteins called GLUT proteins, also known as glucose transporter proteins . These transporters assist in the facilitated diffusion of glucose.

First Half of Glycolysis (Energy-Requiring Steps)

Step 1. The first step in glycolysis (Figure 9.1.1) is catalyzed by hexokinase, an enzyme with broad specificity that catalyzes the phosphorylation of six-carbon sugars. Hexokinase phosphorylates glucose using ATP as the source of the phosphate, producing glucose-6-phosphate, a more reactive form of glucose. This reaction prevents the phosphorylated glucose molecule from continuing to interact with the GLUT proteins, and it can no longer leave the cell because the negatively charged phosphate will not allow it to cross the hydrophobic interior of the plasma membrane.

Step 2 . In the second step of glycolysis, an isomerase converts glucose-6-phosphate into one of its isomers, fructose-6-phosphate. An isomerase is an enzyme that catalyzes the conversion of a molecule into one of its isomers. (This change from phosphoglucose to phosphofructose allows the eventual split of the sugar into two three-carbon molecules.).

Step 3 . The third step is the phosphorylation of fructose-6-phosphate, catalyzed by the enzyme phosphofructokinase. A second ATP molecule donates a high-energy phosphate to fructose-6-phosphate, producing fructose-1,6- bi sphosphate. In this pathway, phosphofructokinase is a rate-limiting enzyme . It is active when the concentration of ADP is high; it is less active when ADP levels are low and the concentration of ATP is high. Thus, if there is “sufficient” ATP in the system, the pathway slows down. This is a type of end product inhibition, since ATP is the end product of glucose catabolism.

Step 4. The newly added high-energy phosphates further destabilize fructose-1,6-bisphosphate. The fourth step in glycolysis employs an enzyme, aldolase, to cleave 1,6-bisphosphate into two three-carbon isomers: dihydroxyacetone-phosphate and glyceraldehyde-3-phosphate.

Step 5 . In the fifth step, an isomerase transforms the dihydroxyacetone-phosphate into its isomer, glyceraldehyde-3-phosphate. Thus, the pathway will continue with two molecules of a single isomer. At this point in the pathway, there is a net investment of energy from two ATP molecules in the breakdown of one glucose molecule.

This illustration shows the steps in the first half of glycolysis. In step one, the enzyme hexokinase uses one ATP molecule in the phosphorylation of glucose. In step two, glucose-6-phosphate is rearranged to form fructose-6-phosphate by phosphoglucose isomerase. In step three, phosphofructokinase uses a second ATP molecule in the phosphorylation of the substrate, forming fructose-1,6-bisphosphate. The enzyme fructose bisphosphate aldose splits the substrate into two, forming glyceraldeyde-3-phosphate and dihydroxyacetone-phosphate. In step 4, triose phosphate isomerase converts the dihydroxyacetone-phosphate into glyceraldehyde-3-phosphate

Second Half of Glycolysis (Energy-Releasing Steps)

So far, glycolysis has cost the cell two ATP molecules and produced two small, three-carbon sugar molecules. Both of these molecules will proceed through the second half of the pathway, and sufficient energy will be extracted to pay back the two ATP molecules used as an initial investment and produce a profit for the cell of two additional ATP molecules and two even higher-energy NADH molecules.

Step 6 . The sixth step in glycolysis (Figure 9.1.2) oxidizes the sugar (glyceraldehyde-3-phosphate), extracting high-energy electrons, which are picked up by the electron carrier NAD + , producing NADH. The sugar is then phosphorylated by the addition of a second phosphate group, producing 1,3-bisphosphoglycerate. Note that the second phosphate group does not require another ATP molecule.

This illustration shows the steps in the second half of glycolysis. In step six, the enzyme glyceraldehydes-3-phosphate dehydrogenase produces one NADH molecule and forms 1,3-bisphosphoglycerate. In step seven, the enzyme phosphoglycerate kinase removes a phosphate group from the substrate, forming one ATP molecule and 3-phosphoglycerate. In step eight, the enzyme phosphoglycerate mutase rearranges the substrate to form 2-phosphoglycerate. In step nine, the enzyme enolase rearranges the substrate to form phosphoenolpyruvate. In step ten, a phosphate group is removed from the substrate, forming one ATP molecule and pyruvate.

Here again is a potential limiting factor for this pathway. The continuation of the reaction depends upon the availability of the oxidized form of the electron carrier, NAD + . Thus, NADH must be continuously oxidized back into NAD +  in order to keep this step going. If NAD +  is not available, the second half of glycolysis slows down or stops. If oxygen is available in the system, the NADH will be oxidized readily, though indirectly, and the high-energy electrons from the hydrogen released in this process will be used to produce ATP. In an environment without oxygen, an alternate pathway (fermentation) can provide the oxidation of NADH to NAD + .

Step 7. In the seventh step, catalyzed by phosphoglycerate kinase (an enzyme named for the reverse reaction), 1,3-bisphosphoglycerate donates a high-energy phosphate to ADP, forming one molecule of ATP. (This is an example of substrate-level phosphorylation.) A carbonyl group on the 1,3-bisphosphoglycerate is oxidized to a carboxyl group, and 3-phosphoglycerate is formed.

Step 8 . In the eighth step, the remaining phosphate group in 3-phosphoglycerate moves from the third carbon to the second carbon, producing 2-phosphoglycerate (an isomer of 3-phosphoglycerate). The enzyme catalyzing this step is a mutase (isomerase).

Step 9. Enolase catalyzes the ninth step. This enzyme causes 2-phosphoglycerate to lose water from its structure; this is a dehydration reaction, resulting in the formation of a double bond that increases the potential energy in the remaining phosphate bond and produces phosphoenolpyruvate (PEP).

Step 10 . The last step in glycolysis is catalyzed by the enzyme pyruvate kinase (the enzyme in this case is named for the reverse reaction of pyruvate’s conversion into PEP) and results in the production of a second ATP molecule by substrate-level phosphorylation and the compound pyruvic acid (or its salt form, pyruvate). Many enzymes in enzymatic pathways are named for the reverse reactions, since the enzyme can catalyze both forward and reverse reactions (these may have been described initially by the reverse reaction that takes place in vitro, under non-physiological conditions).

The net reaction in the transformation of glucose into pyruvate is:

clipboard_ea1edd46a50645437499d763f8e695a31.png

Thus,  two molecules of  ATP  are generated in the conversion of glucose into two molecules of pyruvate . 

Note that the energy released in the anaerobic conversion of glucose into two molecules of pyruvate is -21 kcal mol -1  (- 88 kJ mol -1 ).

The Fates of Pyruvate

Pyruvic acid can be made from glucose through glycolysis, converted back to carbohydrates (such as glucose) via gluconeogenesis, or to fatty acids through acetyl-CoA. It can also be used to construct the amino acid alanine, and it can be converted into ethanol.

Pyruvic acid supplies energy to living cells through the citric acid cycle (also known as the Krebs cycle) when oxygen is present (aerobic respiration); when oxygen is lacking, it ferments to produce lactic acid. Pyruvate is an important chemical compound in biochemistry. It is the output of the anaerobic metabolism of glucose known as glycolysis. One molecule of glucose breaks down into two molecules of pyruvate, which are then used to provide further energy in one of two ways. Pyruvate is converted into acetyl- coenzyme A, which is the main input for a series of reactions known as the Krebs cycle.

The net reaction of converting pyruvate into acetyl CoA and CO 2  is:

clipboard_edf01b5c41606919203cf6849d28940c7.png

Pyruvate is also converted to oxaloacetate by an anaplerotic reaction, which replenishes Krebs cycle intermediates; also, oxaloacetate is used for gluconeogenesis. These reactions are named after Hans Adolf Krebs, the biochemist awarded the 1953 Nobel Prize for physiology, jointly with Fritz Lipmann, for research into metabolic processes. The cycle is also known as the citric acid cycle or tri-carboxylic acid cycle, because citric acid is one of the intermediate compounds formed during the reactions.

If insufficient oxygen is available, the acid is broken down anaerobically, creating lactate in animals and ethanol in plants and microorganisms. Pyruvate from glycolysis is converted by fermentation to lactate using the enzyme lactate dehydrogenase and the coenzyme NADH in lactate fermentation. Alternatively it is converted to acetaldehyde and then to ethanol in alcoholic fermentation.

Pyruvate is a key intersection in the network of metabolic pathways. Pyruvate can be converted into carbohydrates via gluconeogenesis, to fatty acids or energy through acetyl-CoA, to the amino acid alanine, and to ethanol. Therefore, it unites several key metabolic processes.

write a essay on glycolysis

                                                   

                                                               Figure 9.1.3 :   Glycolysis Regulation     

Control of glycolysis is unusual for a metabolic pathway, in that regulation occurs at three enzymatic points:

clipboard_ebd064dc2c8cbc4c614b95fd8e6b83db0.png

Glycolysis is regulated in a reciprocal fashion compared to its corresponding anabolic pathway, gluconeogenesis. Reciprocal regulation occurs when the same molecule or treatment (phosphorylation, for example) has opposite effects on catabolic and anabolic pathways. Reciprocal regulation is important when anabolic and corresponding catabolic pathways are occurring in the same cellular location.

As an example, consider regulation of PFK. It is activated by several molecules, most importantly fructose-2,6- bisphosphate (F2,6BP). This molecule has an inhibitory effect on the corresponding gluconeogenesis enzyme, fructose-1,6-bisphosphatase (F1,6BPase).

You might wonder why pyruvate kinase, the last enzyme in the pathway, is regulated. The answer is simple. Pyruvate kinase catalyzes the most energetically rich reaction of glycolysis. The reaction is favored so strongly in the forward direction that cells must do a ‘two-step’ around it in the reverse direction when making glucose. In other words, it takes two enzymes, two reactions, and two triphosphates to go from pyruvate back to PEP in gluconeogenesis. When cells are needing to make glucose, they can’t be sidetracked by having the PEP they have made in gluconeogenesis be converted directly back to pyruvate by pyruvate kinase. Consequently, pyruvate kinase is inhibited during gluconeogenesis, lest a “futile cycle" occur.

Another interesting control mechanism called feedforward activation involves pyruvate kinase. Pyruvate kinase is activated allosterically by F1,6BP. This molecule is a product of the PFK reaction and a substrate for the aldolase reaction. It should be noted that the aldolase reaction is energetically unfavorable (high +ΔΔG°’), thus allowing F1,6BP to accumulate. When this happens, some of the excess F1,6BP activates pyruvate kinase, which jump-starts the conversion of PEP to pyruvate. The resulting drop in PEP levels has the effect of “pulling" on the reactions preceding pyruvate kinase. As a consequence, the concentrations of G3P and DHAP fall, helping to move the aldolase reaction forward.

Outcomes of Glycolysis

Glycolysis starts with one molecule of glucose and ends with two pyruvate (pyruvic acid) molecules, a total of four ATP molecules, and two molecules of NADH. Two ATP molecules were used in the first half of the pathway to prepare the six-carbon ring for cleavage, so the cell has a net gain of two ATP molecules and 2 NADH molecules for its use. If the cell cannot catabolize the pyruvate molecules further (via the citric acid cycle or Krebs cycle), it will harvest only two ATP molecules from one molecule of glucose.

Mature mammalian red blood cells do not have mitochondria and are not capable of aerobic respiration, the process in which organisms convert energy in the presence of oxygen. Instead, glycolysis is their sole source of ATP. Therefore, if glycolysis is interrupted, the red blood cells lose their ability to maintain their sodium-potassium pumps, which require ATP to function, and eventually, they die. For example, since the second half of glycolysis (which produces the energy molecules) slows or stops in the absence of NAD + , when NAD + is unavailable, red blood cells will be unable to produce a sufficient amount of ATP in order to survive.

Additionally, the last step in glycolysis will not occur if pyruvate kinase, the enzyme that catalyzes the formation of pyruvate, is not available in sufficient quantities. In this situation, the entire glycolysis pathway will continue to proceed, but only two ATP molecules will be made in the second half (instead of the usual four ATP molecules). Thus, pyruvate kinase is a rate-limiting enzyme for glycolysis.

Contributors 

  • Darik Benson, (University California Davis)
  • Dr. Kevin Ahern  and  Dr. Indira Rajagopal  (Oregon State University)

Glycolysis Process in Yeast and in Human Report

Glycolysis is a series of reactions that converts glucose into pyruvate and produce small amounts of ATP (adenosine triphosphate). The overall process of sugar breakdown to produce energy, however, is called respiration, and it takes several biochemical reactions, including glycolysis.

The process of glycolysis is very important in the human body. It is a part of the respiration process where energy is produced in our bodies. Glycolysis is the process whereby sugar is broken down to produce energy in the human body. This process is catalyzed by about ten enzymes which include, Kinases, Isomerases, and dehydrogenases, which are the key player enzymes in this process. In the process of glycolysis, sugar gets oxidized and released in the form of energy ATP energy. Glycolysis assists the body in the production of energy under low energy and inactive muscles. (Romano, 1996 pp. 234-289).

Energy containing sugars that are referred to as Hexoses which include galactose and fructose are funneled into glycolysis and produce energy in the human body. Human bodies have several metabolic processes to choose from, anabolic or catabolic, that are available from the sugars we consume. However, this depends on the energy that we require in our cells. When we are less active, the energy produced from the sugars will be stored as glycogen or fat for use when needed. When our bodies are active, the body cells often run out of adequate energy. The sugars are instantly broken down to produce energy, and the energy is released instantly into the cells. Energy from glucose is stored in various forms. The main form of storage is glycogen. The synthesis and the breakdown process of glycogen are controlled by a hormone called insulin. Long-term energy storage in cells is the conversion of energy, especially bulk energy, to fats that are stored in the body muscles. Glycolysis plays a very important role in the conversion process of energy to fats. Though it is a single part of the catabolic process, it is an ideal model of energy conversion. The bodies have a choice on what to do with the food we eat. (Robert, 2004 pp. 112- 201).

In yeast, the glycolysis process is a fermentation reaction, and it takes the following general equation;

glucose + 2ADP + 2P = 2CO2 + 2ATP. The difference between glucose, ethanol, and carbon dioxide, ADP, and ATP is that glucose, ethanol, and carbon dioxide are external substrates as well as products, and they are ingested and excreted, forming natural metabolic boundaries. The other two that is, ATP and ADP are which are the internal substrates and products, form artificial metabolic boundaries and connect with other cellular processes. The end products from these external substrates are from other cellular processes; for example, ATP is used in biosynthesis and growth while amino acids are for protein synthesis, and nucleotides synthesize nucleic acid. The process of glycolysis in yeast is basically anaerobic as I fermentation of yeast the process do not require oxygen or takes place in low oxygen concentration. In human beings, however, the process takes place only at a high concentration of oxygen as it involves the oxidation of sugars to release energy. Glycolysis in humans that is aerobic produces more energy from glucose than in anaerobic glycolysis in yeast which relies on the energy of glycolysis alone. The end product in glycolysis in yeast is lactate, while in humans, carbon dioxide and water are produced as by-products after energy is produced. In human cells, sometimes anaerobic glycolysis takes place in red blood cells and in some skeletal muscles where there is a shortage of oxygen. Higher demand of energy, for example, in the increase in cells, may cause the process of glycolysis to take place at low oxygen levels even in human beings.

Romano, H. (1996). Evolution of Carbohydrate Metabolic Pathways , New York: Prentice-Hall, pp. 211- 345.

Voet, D. and Voet, J. (2004). Biochemistry, 3rd Edition, New York: John Wisley and Sons inc. pp. 112- 205.

Robert, A. (2004). Life on Earth , 4th Edition, New York: MacGraw Hill, pp. 112-213.

  • Chicago (A-D)
  • Chicago (N-B)

IvyPanda. (2021, October 26). Glycolysis Process in Yeast and in Human. https://ivypanda.com/essays/glycolysis-process-in-yeast-and-in-human/

"Glycolysis Process in Yeast and in Human." IvyPanda , 26 Oct. 2021, ivypanda.com/essays/glycolysis-process-in-yeast-and-in-human/.

IvyPanda . (2021) 'Glycolysis Process in Yeast and in Human'. 26 October.

IvyPanda . 2021. "Glycolysis Process in Yeast and in Human." October 26, 2021. https://ivypanda.com/essays/glycolysis-process-in-yeast-and-in-human/.

1. IvyPanda . "Glycolysis Process in Yeast and in Human." October 26, 2021. https://ivypanda.com/essays/glycolysis-process-in-yeast-and-in-human/.

Bibliography

IvyPanda . "Glycolysis Process in Yeast and in Human." October 26, 2021. https://ivypanda.com/essays/glycolysis-process-in-yeast-and-in-human/.

  • Measurement of the Rate of Glycolysis Using Saccharomyces Cerevisae
  • Glycolysis Process and Regulation
  • The Complexity of Photosynthesis and Respiration
  • Photosynthesis, Fermentation, and Enzyme Activity
  • Cellular Respiration in Context of Human Biology
  • Biology: Photosynthesis and Respiration
  • Enzymology and Catalytic Mechanism
  • Cell Energy Metabolism Controls
  • Adenosine Triphosphate, Energy and Phosphorylation
  • Anaerobic Respiration and Its Applications
  • Biology: Coral Reef and Its Diseases
  • Color Vision in Human Beings and Other Mammals
  • The Concept of Founder Mutations
  • Neurotransmitters. The Process of Signal Transmission
  • Botany and Taxonomy of the Onion

Home — Essay Samples — Science — Cell — Phases of Glycolysis

test_template

Phases of Glycolysis

  • Categories: Cell Glucose

About this sample

close

Words: 1884 |

10 min read

Published: Oct 11, 2018

Words: 1884 | Pages: 4 | 10 min read

Image of Alex Wood

Cite this Essay

Let us write you an essay from scratch

  • 450+ experts on 30 subjects ready to help
  • Custom essay delivered in as few as 3 hours

Get high-quality help

author

Verified writer

  • Expert in: Science Nursing & Health

writer

+ 120 experts online

By clicking “Check Writers’ Offers”, you agree to our terms of service and privacy policy . We’ll occasionally send you promo and account related email

No need to pay just yet!

Related Essays

1 pages / 513 words

1 pages / 407 words

2 pages / 820 words

3 pages / 1322 words

Remember! This is just a sample.

You can get your custom paper by one of our expert writers.

121 writers online

Phases of Glycolysis Essay

Still can’t find what you need?

Browse our vast selection of original essay samples, each expertly formatted and styled

Related Essays on Cell

Prokaryotic and eukaryotic cells are the two main types of cells that make up all living organisms. Despite their differences, there are several striking similarities between prokaryotic and eukaryotic cells that point to their [...]

Animal cells, the fundamental building blocks of life, harbor a remarkable complexity of structures and functions. This essay delves into the intricacies of animal cell machinery, exploring the vital components that enable [...]

Polymers are large molecules and have the same structural unit repeating over and over and these repeating units are known as monomers. These monomers are attached with each other with covalent bonds and form polymers. Polymers [...]

" Before delving into the adverse effects of changes of pH in our body it’s important to understand what pH is. pH is a measure of hydrogen ion concentration or how acidic or alkaline a substance is on a scale ranging from 1 to [...]

Nerve cells also are known as neurons transmit and receive electro nerve impulses. They can be found all over the body and are connected all over the body, but can mostly be found near around the Central Nervous System. They are [...]

A collection of cells performing a specific function is called tissue. Plant tissues can be grouped into plant tissue systems each performing specialized functions. A plant tissue system is defined as a functional unit, [...]

Related Topics

By clicking “Send”, you agree to our Terms of service and Privacy statement . We will occasionally send you account related emails.

Where do you want us to send this sample?

By clicking “Continue”, you agree to our terms of service and privacy policy.

Be careful. This essay is not unique

This essay was donated by a student and is likely to have been used and submitted before

Download this Sample

Free samples may contain mistakes and not unique parts

Sorry, we could not paraphrase this essay. Our professional writers can rewrite it and get you a unique paper.

Please check your inbox.

We can write you a custom essay that will follow your exact instructions and meet the deadlines. Let's fix your grades together!

Get Your Personalized Essay in 3 Hours or Less!

We use cookies to personalyze your web-site experience. By continuing we’ll assume you board with our cookie policy .

  • Instructions Followed To The Letter
  • Deadlines Met At Every Stage
  • Unique And Plagiarism Free

write a essay on glycolysis

Talk to our experts

1800-120-456-456

Write a short note on glycolysis.

seo images

Repeaters Course for NEET 2022 - 23

We use cookies to enhance our website for you. Proceed if you agree to this policy or learn more about it.

  • Essay Database >
  • Essays Examples >
  • Essay Topics

Essays on Glycolysis

26 samples on this topic

On this page, we've put together a catalog of free paper samples regarding Glycolysis. The plan is to provide you with a sample similar to your Glycolysis essay topic so that you could have a closer look at it in order to get a clear idea of what a top-notch academic work should look like. You are also recommended to implement the best Glycolysis writing practices revealed by competent authors and, eventually, come up with a high-quality paper of your own.

However, if crafting Glycolysis papers entirely by yourself is not an option at this point, WowEssays.com essay writer service might still be able to help you out. For example, our writers can write an one-of-a-kind Glycolysis essay sample specifically for you. This example paper on Glycolysis will be written from scratch and tailored to your custom requirements, fairly priced, and delivered to you within the pre-set deadline. Choose your writer and buy custom essay now!

Perfect Model Essay On Fats

Percentage of fat the athlete’s diet

What Happens In Different Nutrient Conditions?: Free Sample Literature Review To Follow

Vid30 complex participation in the degradation of CDC25 in yeast and their role in Ras/ cAMP/ PKA pathway

Free Essay About Cellular Respiration And Photosynthesis

Introduction

Course Work On Biochemistry

Q. 1. Explain how gel filtration chromatography (size exclusion chromatography) separates molecules on the basis of their mass/size.

Good Dissertation On Biology

Biology Assignment

The Warburg Effect Article Review Samples

- The Warburg effect was an observation found in cancer cells by a German biochemist Otto Heinrich Warburg. He was able to observe that in cancer cells, there is a high rate of glycolysis under aerobic conditions, a trait which is technically inefficient for energy production in multicellular organisms. Hence due to his discovery, it subsequently also became known as the “Warburg Effect” over the years.

- Apparently Warburg was wrong. It was said in the paper that not all cancer cells have their mitochondria improperly functioning.

Involvement of Enzymes in Fructose Decomposition Course Work Examples

Living organisms depend on biochemistry to power various chemical reaction cycles which are important for the overall biological functioning of an organism. Chemical reactions occur at a specific rate in certain conditions and require input energy (activation energy) to be supplied before a reaction can begin. Since a reaction cycle consist of many consecutive step, slowing one step slows down the whole cycle. Enzymes are proteins which act as catalysts in biochemical reactions and speeds up reactions to rates that are high enough for biological functioning. Enzymes manage this by providing an alternative reaction route with lower activation energy.

Example Of Biochemistry Assignment Course Work

Report on Case 1: Diagnosis of Hereditary Fructose Intolerance

Photosynthesis Course Work

Good article review on human mesenchymal stem cells, good research paper about recommended level of macronutrient intake for harvey kent.

Harvey requires enough energy to perform. Consequently, he must consume enough calories to meet all his energy needs. The actual requirement for calorie intake depends on one’s level of fitness and bodyweight. In addition, the intensity, frequency, and duration of physical activity also greatly influence one’s actual energy requirement.

Carbohydrates

Free Report About Some Of The Electron Carriers, Including Cytochromes, Are Similar Both In Chloroplast

Section Number.

Good Cell Respiration Glycolysis And Co2 Production Report Example

Essay on anatomy and pharmacy paper, example of essay on climate, membranes, enzymes and metabolic pathways, bioenergetics and respiration, free essay on topics in metabolism, lactate threshold essay example, example of nutrition: the metabolism of carbohydrates in terms or monosaccharide and polysaccharides essay.

(City, State)

Essay On Cells Biochemical Evidence For Evolution

Marathon versus sprint runners research paper examples, photosynthesis essay examples, material and methods report examples, advanced exercise physiology essay examples, cell reproduction research paper examples.

Cell Reproduction

Mitochondrial Disease Case Study

The doctor suspects mitochondrial disease which can occur at multiple levels in different mitochondrial processes. To help the doctor determine where the defect might have occurred:

1. Explain what would happen if the interconversions of the Cori cycle occurred and remained within a single cell.

275 words = 1 page double-spaced

submit your paper

Password recovery email has been sent to [email protected]

Use your new password to log in

You are not register!

By clicking Register, you agree to our Terms of Service and that you have read our Privacy Policy .

Now you can download documents directly to your device!

Check your email! An email with your password has already been sent to you! Now you can download documents directly to your device.

or Use the QR code to Save this Paper to Your Phone

The sample is NOT original!

Short on a deadline?

Don't waste time. Get help with 11% off using code - GETWOWED

No, thanks! I'm fine with missing my deadline

Ultimate Guide to Writing Your College Essay

Tips for writing an effective college essay.

College admissions essays are an important part of your college application and gives you the chance to show colleges and universities your character and experiences. This guide will give you tips to write an effective college essay.

Want free help with your college essay?

UPchieve connects you with knowledgeable and friendly college advisors—online, 24/7, and completely free. Get 1:1 help brainstorming topics, outlining your essay, revising a draft, or editing grammar.

 alt=

Writing a strong college admissions essay

Learn about the elements of a solid admissions essay.

Avoiding common admissions essay mistakes

Learn some of the most common mistakes made on college essays

Brainstorming tips for your college essay

Stuck on what to write your college essay about? Here are some exercises to help you get started.

How formal should the tone of your college essay be?

Learn how formal your college essay should be and get tips on how to bring out your natural voice.

Taking your college essay to the next level

Hear an admissions expert discuss the appropriate level of depth necessary in your college essay.

Student Stories

 alt=

Student Story: Admissions essay about a formative experience

Get the perspective of a current college student on how he approached the admissions essay.

Student Story: Admissions essay about personal identity

Get the perspective of a current college student on how she approached the admissions essay.

Student Story: Admissions essay about community impact

Student story: admissions essay about a past mistake, how to write a college application essay, tips for writing an effective application essay, sample college essay 1 with feedback, sample college essay 2 with feedback.

This content is licensed by Khan Academy and is available for free at www.khanacademy.org.

  • Share full article

Advertisement

Supported by

Guest Essay

A.I.-Generated Garbage Is Polluting Our Culture

A colorful illustration of a series of blue figures lined up on a bright pink floor with a red background. The farthest-left figure is that of a robot; every subsequent figure is slightly more mutated until the final figure at the right is strangely disfigured.

By Erik Hoel

Mr. Hoel is a neuroscientist and novelist and the author of The Intrinsic Perspective newsletter.

Increasingly, mounds of synthetic A.I.-generated outputs drift across our feeds and our searches. The stakes go far beyond what’s on our screens. The entire culture is becoming affected by A.I.’s runoff, an insidious creep into our most important institutions.

Consider science. Right after the blockbuster release of GPT-4, the latest artificial intelligence model from OpenAI and one of the most advanced in existence, the language of scientific research began to mutate. Especially within the field of A.I. itself.

write a essay on glycolysis

Adjectives associated with A.I.-generated text have increased in peer reviews of scientific papers about A.I.

Frequency of adjectives per one million words

Commendable

write a essay on glycolysis

A study published this month examined scientists’ peer reviews — researchers’ official pronouncements on others’ work that form the bedrock of scientific progress — across a number of high-profile and prestigious scientific conferences studying A.I. At one such conference, those peer reviews used the word “meticulous” more than 34 times as often as reviews did the previous year. Use of “commendable” was around 10 times as frequent, and “intricate,” 11 times. Other major conferences showed similar patterns.

Such phrasings are, of course, some of the favorite buzzwords of modern large language models like ChatGPT. In other words, significant numbers of researchers at A.I. conferences were caught handing their peer review of others’ work over to A.I. — or, at minimum, writing them with lots of A.I. assistance. And the closer to the deadline the submitted reviews were received, the more A.I. usage was found in them.

If this makes you uncomfortable — especially given A.I.’s current unreliability — or if you think that maybe it shouldn’t be A.I.s reviewing science but the scientists themselves, those feelings highlight the paradox at the core of this technology: It’s unclear what the ethical line is between scam and regular usage. Some A.I.-generated scams are easy to identify, like the medical journal paper featuring a cartoon rat sporting enormous genitalia. Many others are more insidious, like the mislabeled and hallucinated regulatory pathway described in that same paper — a paper that was peer reviewed as well (perhaps, one might speculate, by another A.I.?).

What about when A.I. is used in one of its intended ways — to assist with writing? Recently, there was an uproar when it became obvious that simple searches of scientific databases returned phrases like “As an A.I. language model” in places where authors relying on A.I. had forgotten to cover their tracks. If the same authors had simply deleted those accidental watermarks, would their use of A.I. to write their papers have been fine?

What’s going on in science is a microcosm of a much bigger problem. Post on social media? Any viral post on X now almost certainly includes A.I.-generated replies, from summaries of the original post to reactions written in ChatGPT’s bland Wikipedia-voice, all to farm for follows. Instagram is filling up with A.I.-generated models, Spotify with A.I.-generated songs. Publish a book? Soon after, on Amazon there will often appear A.I.-generated “workbooks” for sale that supposedly accompany your book (which are incorrect in their content; I know because this happened to me). Top Google search results are now often A.I.-generated images or articles. Major media outlets like Sports Illustrated have been creating A.I.-generated articles attributed to equally fake author profiles. Marketers who sell search engine optimization methods openly brag about using A.I. to create thousands of spammed articles to steal traffic from competitors.

Then there is the growing use of generative A.I. to scale the creation of cheap synthetic videos for children on YouTube. Some example outputs are Lovecraftian horrors, like music videos about parrots in which the birds have eyes within eyes, beaks within beaks, morphing unfathomably while singing in an artificial voice, “The parrot in the tree says hello, hello!” The narratives make no sense, characters appear and disappear randomly, and basic facts like the names of shapes are wrong. After I identified a number of such suspicious channels on my newsletter, The Intrinsic Perspective, Wired found evidence of generative A.I. use in the production pipelines of some accounts with hundreds of thousands or even millions of subscribers.

As a neuroscientist, this worries me. Isn’t it possible that human culture contains within it cognitive micronutrients — things like cohesive sentences, narrations and character continuity — that developing brains need? Einstein supposedly said : “If you want your children to be intelligent, read them fairy tales. If you want them to be very intelligent, read them more fairy tales.” But what happens when a toddler is consuming mostly A.I.-generated dream-slop? We find ourselves in the midst of a vast developmental experiment.

There’s so much synthetic garbage on the internet now that A.I. companies and researchers are themselves worried, not about the health of the culture, but about what’s going to happen with their models. As A.I. capabilities ramped up in 2022, I wrote on the risk of culture’s becoming so inundated with A.I. creations that when future A.I.s are trained, the previous A.I. output will leak into the training set, leading to a future of copies of copies of copies, as content became ever more stereotyped and predictable. In 2023 researchers introduced a technical term for how this risk affected A.I. training: model collapse . In a way, we and these companies are in the same boat, paddling through the same sludge streaming into our cultural ocean.

With that unpleasant analogy in mind, it’s worth looking to what is arguably the clearest historical analogy for our current situation: the environmental movement and climate change. For just as companies and individuals were driven to pollute by the inexorable economics of it, so, too, is A.I.’s cultural pollution driven by a rational decision to fill the internet’s voracious appetite for content as cheaply as possible. While environmental problems are nowhere near solved, there has been undeniable progress that has kept our cities mostly free of smog and our lakes mostly free of sewage. How?

Before any specific policy solution was the acknowledgment that environmental pollution was a problem in need of outside legislation. Influential to this view was a perspective developed in 1968 by Garrett Hardin, a biologist and ecologist. Dr. Hardin emphasized that the problem of pollution was driven by people acting in their own interest, and that therefore “we are locked into a system of ‘fouling our own nest,’ so long as we behave only as independent, rational, free-enterprisers.” He summed up the problem as a “tragedy of the commons.” This framing was instrumental for the environmental movement, which would come to rely on government regulation to do what companies alone could or would not.

Once again we find ourselves enacting a tragedy of the commons: short-term economic self-interest encourages using cheap A.I. content to maximize clicks and views, which in turn pollutes our culture and even weakens our grasp on reality. And so far, major A.I. companies are refusing to pursue advanced ways to identify A.I.’s handiwork — which they could do by adding subtle statistical patterns hidden in word use or in the pixels of images.

A common justification for inaction is that human editors can always fiddle around with whatever patterns are used if they know enough. Yet many of the issues we’re experiencing are not caused by motivated and technically skilled malicious actors; they’re caused mostly by regular users’ not adhering to a line of ethical use so fine as to be nigh nonexistent. Most would be uninterested in advanced countermeasures to statistical patterns enforced into outputs that should, ideally, mark them as A.I.-generated.

That’s why the independent researchers were able to detect A.I. outputs in the peer review system with surprisingly high accuracy: They actually tried. Similarly, right now teachers across the nation have created home-brewed output-side detection methods , like adding hidden requests for patterns of word use to essay prompts that appear only when copied and pasted.

In particular, A.I. companies appear opposed to any patterns baked into their output that can improve A.I.-detection efforts to reasonable levels, perhaps because they fear that enforcing such patterns might interfere with the model’s performance by constraining its outputs too much — although there is no current evidence this is a risk. Despite public pledges to develop more advanced watermarking, it’s increasingly clear that the companies are dragging their feet because it goes against the A.I. industry’s bottom line to have detectable products.

To deal with this corporate refusal to act we need the equivalent of a Clean Air Act: a Clean Internet Act. Perhaps the simplest solution would be to legislatively force advanced watermarking intrinsic to generated outputs, like patterns not easily removable. Just as the 20th century required extensive interventions to protect the shared environment, the 21st century is going to require extensive interventions to protect a different, but equally critical, common resource, one we haven’t noticed up until now since it was never under threat: our shared human culture.

Erik Hoel is a neuroscientist, a novelist and the author of The Intrinsic Perspective newsletter.

The Times is committed to publishing a diversity of letters to the editor. We’d like to hear what you think about this or any of our articles. Here are some tips . And here’s our email: [email protected] .

Follow the New York Times Opinion section on Facebook , Instagram , TikTok , WhatsApp , X and Threads .

IMAGES

  1. Give the schematic representation of glycolysis

    write a essay on glycolysis

  2. Glycolysis

    write a essay on glycolysis

  3. Glycolysis_gap_fill

    write a essay on glycolysis

  4. Essay Explaining the Process of Glycolysis

    write a essay on glycolysis

  5. Glycolysis as a Biological Process

    write a essay on glycolysis

  6. Glycolysis

    write a essay on glycolysis

VIDEO

  1. Glycolysis...#biology #cellbiology #biochemistry

  2. Chapter 9 Part 1 : Cellular Respiration

  3. GLYCOLYSIS CYCLE #EMP PATHWAY #GLYCOLYSIS KYA HAI #IMPORTANT OF GLYCOLYSIS CYCLE #USE OF GLYCOLYSIS

  4. Studying the glycolysis pathway

  5. Glycolysis full explanation in easy way!

  6. Glycolysis with Structures and Enzymes

COMMENTS

  1. Glycolysis

    Glycolysis takes place in the cytosol of a cell, and it can be broken down into two main phases: the energy-requiring phase, above the dotted line in the image below, and the energy-releasing phase, below the dotted line. Energy-requiring phase. In this phase, the starting molecule of glucose gets rearranged, and two phosphate groups are ...

  2. Glycolysis

    Glycolysis is the primary step of cellular respiration, which occurs in all organisms. Glycolysis is followed by the Krebs cycle during aerobic respiration. In the absence of oxygen, the cells make small amounts of ATP as glycolysis is followed by fermentation. This metabolic pathway was discovered by three German biochemists- Gustav Embden ...

  3. Glycolysis Explained in 10 Easy Steps

    Steps 1 and 3 = - 2ATP. Steps 7 and 10 = + 4 ATP. Net "visible" ATP produced = 2. Immediately upon finishing glycolysis, the cell must continue respiration in either an aerobic or anaerobic direction; this choice is made based on the circumstances of the particular cell. A cell that can perform aerobic respiration and which finds itself ...

  4. Biochemistry, Glycolysis

    Glycolysis is a metabolic pathway and an anaerobic energy source that has evolved in nearly all types of organisms. Another name for the process is the Embden-Meyerhof pathway, in honor of the major contributors towards its discovery and understanding.[1] Although it doesn't require oxygen, hence its purpose in anaerobic respiration, it is also the first step in cellular respiration.

  5. The 10 Steps of Glycolysis

    Glycolysis, which translates to "splitting sugars", is the process of releasing energy within sugars. In glycolysis, a six-carbon sugar known as glucose is split into two molecules of a three-carbon sugar called pyruvate. This multistep process yields two ATP molecules containing free energy, two pyruvate molecules, two high energy, electron-carrying molecules of NADH, and two molecules of water.

  6. Aerobic Respiration, Part 1: Glycolysis

    Glycolysis is the first pathway used in the breakdown of glucose to extract energy. It was probably one of the earliest metabolic pathways to evolve and is used by nearly all of the organisms on earth. Glycolysis consists of two parts: The first part prepares the six-carbon ring of glucose for cleavage into two three-carbon sugars. ATP is ...

  7. Glycolysis as a Biological Process

    Words: 623 Pages: 2. Glycolysis is a biological term used to describe reactions that extract energy from glucose by dividing it into two three-carbon molecules named pyruvates. It is an old metabolic pathway found in most living organisms (Chandel, 2021). The term glycolysis is derived from the root of two words, namely glycol, which stands for ...

  8. Glycolysis : The Pathway and Key Events In Glycolysis Process

    The overall process of glycolysis is an oxidation reaction. In this reaction, glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate, which involves the oxidation of an aldehyde group to a carboxylic acid group. The electrons that are lost by glyceraldehyde-3-phosphate are taken up by NAD +, which gets reduced to NADH.

  9. Overview of glycolysis (video)

    Overview of glycolysis. Let's explore the process of glycolysis, the first phase of cellular respiration. Learn how this process breaks down glucose into two 3-carbon compounds, using two ATPs in the investment phase and generating a net of two ATPs in the payoff phase. Created by Sal Khan.

  10. 9.3: Glycolysis

    Step 8. In the eighth step, the remaining phosphate group in 3-phosphoglycerate moves from the third carbon to the second carbon, producing 2-phosphoglycerate (an isomer of 3-phosphoglycerate). The enzyme catalyzing this step is a mutase (isomerase). Step 9. Enolase catalyzes the ninth step.

  11. Glycolysis: Introduction

    In the first two sections of this SparkNote, we will look at glycolysis in two major stages. The first involves the phosphorylation of the glucose ring in preparation for an eventual breakdown into two 3-carbon molecules. In the second stage, the two 3-carbon molecules are converted into pyruvate. Glycolysis quiz that tests what you know about ...

  12. Glycolysis Process and Its Stages

    Glycolysis is a process of splitting 6-carbon glucose into two molecules of pyruvate, which is 3-carbon. This process is also known as the Embden-Meyerhof Pathway, and it involves several steps to cover all reactions (Mauseth, 2014, p. 245; Stoker, 2012). The process occurs in the cytosol of the cytoplasm of a cell (Stoker, 2012, p. 907).

  13. Compartmentalization and metabolic regulation of glycolysis

    Introduction. Glycolysis is a core energy-producing pathway in cells; it converts glucose to two net ATPs and pyruvates, which can then be utilized by the mitochondria to generate an additional 34 ATPs through oxidative phosphorylation in the tricarboxylic acid (TCA) cycle (Al Tameemi et al., 2019) (Fig. 1).Hypoxic stress precludes the function of the highly efficient oxidative phosphorylation ...

  14. Glycolysis

    Biology definition: Glycolysis is a series of reactions happening in the cytosol that results in the conversion of a monosaccharide, often glucose, into pyruvate, and the concomitant production of a relatively small amount of high-energy biomolecules, such as ATP.It is the initial metabolic pathway of cellular respiration.. Cellular respiration is a series of metabolic processes wherein the ...

  15. 5.2.3 Glycolysis

    Aerobic Respiration: Glycolysis. Glycolysis is the first stage of respiration. It takes place in the cytoplasm of the cell and involves: Trapping glucose in the cell by phosphorylating the molecule. Splitting the glucose molecule in two. It results in the production of. 2 Pyruvate (3C) molecules. Net gain 2 ATP. 2 reduced NAD.

  16. 9.1: Glycolysis

    Darik Benson, (University California Davis) Dr. Kevin Ahern and Dr. Indira Rajagopal (Oregon State University) 9.1: Glycolysis - Reaction and Regulation is shared under a license and was authored, remixed, and/or curated by LibreTexts. Glycolysis begins with the six carbon ring-shaped structure of a single glucose molecule and ends with two ...

  17. Glycolysis Process and Regulation

    Glycolysis starts with the rearrangement of the glucose molecule, where it receives two extra phosphate groups from ATP. The modified molecule is called fructose-1,6-bisphosphate, and it has two three-carbon sugars with phosphate groups attached. This process uses 2 ATP molecules to produce phosphate groups. This step makes the sugar molecule ...

  18. Glycolysis Process in Yeast and in Human Report

    Glycolysis is the process whereby sugar is broken down to produce energy in the human body. This process is catalyzed by about ten enzymes which include, Kinases, Isomerases, and dehydrogenases, which are the key player enzymes in this process. In the process of glycolysis, sugar gets oxidized and released in the form of energy ATP energy.

  19. Phases of Glycolysis: [Essay Example], 1884 words GradesFixer

    The first five steps of the glycolysis reaction are known as the preparatory or investment phase. This stage consumes energy to convert the glucose molecule into two molecules three-carbon sugar molecule. Step 1. The step one in glycolysis is phosphorylation. This step glucose is phosphorylated by the enzyme hexokinases.

  20. Write a short note on glycolysis.

    Hint: Glycolysis is an anaerobic process that takes place in the cell cytoplasm. Glycolysis is the stage where 1 glucose molecule is broken down into 2 molecules of pyruvate along with the release of energy. The glycolysis cycle begins when the glucose molecule is broken down due to certain conditions and results in the formation of the two ...

  21. Glycolysis Essay Examples

    For example, our writers can write an one-of-a-kind Glycolysis essay sample specifically for you. This example paper on Glycolysis will be written from scratch and tailored to your custom requirements, fairly priced, and delivered to you within the pre-set deadline. Choose your writer and buy custom essay now!

  22. Glycolysis Essay

    1. Glycolysis is an essential anaerobic pathway for ATP production in the body. There are various steps and processes that occur and lead to the production of various products and most importantly ATP. Let's dive right into it and get started on the process of glycolysis. Glycolysis occurs in the cytosol of the cell and can be divided into ...

  23. Ultimate Guide to Writing Your College Essay

    Sample College Essay 2 with Feedback. This content is licensed by Khan Academy and is available for free at www.khanacademy.org. College essays are an important part of your college application and give you the chance to show colleges and universities your personality. This guide will give you tips on how to write an effective college essay.

  24. Glycolysis: Study Guide

    Biology (SparkCharts) Buy Now. View all Available Study Guides. From a general summary to chapter summaries to explanations of famous quotes, the SparkNotes Glycolysis Study Guide has everything you need to ace quizzes, tests, and essays.

  25. Opinion

    1025. By José Andrés. Mr. Andrés is the founder of World Central Kitchen. Leer en español. In the worst conditions you can imagine — after hurricanes, earthquakes, bombs and gunfire — the ...

  26. AI Garbage Is Already Polluting the Internet

    A.I.-Generated Garbage Is Polluting Our Culture. Mr. Hoel is a neuroscientist and novelist and the author of The Intrinsic Perspective newsletter. Increasingly, mounds of synthetic A.I.-generated ...