aqa a level biology enzymes essay

Enzymes are proteins that catalyse reactions. The chemical reactants that enzymes bind to are called substrates.

Biological catalyst

• A substance that speeds up a chemical reaction without being used up itself is a catalyst.
• Enzymes are proteins that catalyse biochemical reactions.
• Enzymes can act inside or outside of cells.

Activation energy

• This is called the activation energy.

Activation energy and enzymes

• Enzymes lower the activation energies of chemical reactions inside the cell to increase the rate of reactions.
• Enzymes lower the activation energy by binding to the reactant molecules (substrate) and allowing chemical bond-breaking and bond-forming processes to happen more easily.

The active site

• Enzymes catalyse specific reactions.
• The active site has a specific shape for each enzyme.
• Substrates with a complementary shape to the active site of an enzyme can bind to form an enzyme-substrate complex.
• The shape of the active site is determined by the tertiary structure of the polypeptide.

Models of Enzyme Action

Models of enzyme action have changed over time. For many years, it was thought that enzymes worked in a lock and key manner. The induced fit model is now more widely accepted.

The lock and key model

• The lock and key model was originally used to explain enzyme action.
• The substrate is a key fitting into a lock (the enzyme).

The induced fit model

• The induced fit model suggests there is a more dynamic interaction between enzyme and substrate.
• The model states that as an enzyme and substrate come together, their interaction causes a small shift in the enzyme’s structure.
• The shift means that the enzyme and substrate can bind to form an enzyme-substrate complex and catalyse a reaction.
• This model is now more widely accepted.

Enzyme-Substrate Complexes

Enzymes bind with substrates to form an enzyme-substrate complex in a specific fashion. The specificity of enzymes is determined by two things:

Active site

• Every enzyme only catalyses one specific reaction.
• This jigsaw puzzle-like match between an enzyme and its substrates is what makes enzymes highly specific.

Environmental factors

• The 3D, tertiary structure of the polypetide chain determines the shape of the active site.
• This is called a denatured enzyme.

1 Biological Molecules

1.1 Monomers & Polymers

1.1.1 Monomers & Polymers

1.1.2 Condensation & Hydrolysis Reactions

1.2 Carbohydrates

1.2.1 Structure of Carbohydrates

1.2.2 Types of Polysaccharides

1.2.3 End of Topic Test - Monomers, Polymers and Carbs

1.2.4 Exam-Style Question - Carbohydrates

1.2.5 A-A* (AO3/4) - Carbohydrates

1.3.1 Triglycerides & Phospholipids

1.3.2 Types of Fatty Acids

1.3.3 Testing for Lipids

1.3.4 Exam-Style Question - Fats

1.3.5 A-A* (AO3/4) - Lipids

1.4 Proteins

1.4.1 The Peptide Chain

1.4.2 Investigating Proteins

1.4.3 Primary & Secondary Protein Structure

1.4.4 Tertiary & Quaternary Protein Structure

1.4.5 Enzymes

1.4.6 Factors Affecting Enzyme Activity

1.4.7 Enzyme-Controlled Reactions

1.4.8 End of Topic Test - Lipids & Proteins

1.4.9 A-A* (AO3/4) - Enzymes

1.4.10 A-A* (AO3/4) - Proteins

1.5 Nucleic Acids

1.5.1 DNA & RNA

1.5.2 Polynucleotides

1.5.3 DNA Replication

1.5.4 Exam-Style Question - Nucleic Acids

1.5.5 A-A* (AO3/4) - Nucleic Acids

1.6.1 Structure of ATP

1.6.2 End of Topic Test - Nucleic Acids & ATP

1.7.1 Structure & Function of Water

1.7.2 A-A* (AO3/4) - Water

1.8 Inorganic Ions

1.8.1 Inorganic Ions

1.8.2 End of Topic Test - Water & Inorganic Ions

2.1 Cell Structure

2.1.1 Introduction to Cells

2.1.2 Eukaryotic Cells & Organelles

2.1.3 Eukaryotic Cells & Organelles 2

2.1.4 Prokaryotes

2.1.5 A-A* (AO3/4) - Organelles

2.1.6 Methods of Studying Cells

2.1.7 Microscopes

2.1.8 End of Topic Test - Cell Structure

2.1.9 Exam-Style Question - Cells

2.1.10 A-A* (AO3/4) - Cells

2.2 Mitosis & Cancer

2.2.1 Mitosis

2.2.2 Investigating Mitosis

2.2.3 Cancer

2.2.4 A-A* (AO3/4) - The Cell Cycle

2.3 Transport Across Cell Membrane

2.3.1 Cell Membrane Structure

2.3.2 A-A* (AO3/4) - Membrane Structure

2.3.3 Diffusion

2.3.4 Osmosis

2.3.5 Active Transport

2.3.6 End of Topic Test - Mitosis, Cancer & Transport

2.3.7 Exam-Style Question - Membranes

2.3.8 A-A* (AO3/4) - Membranes & Transport

2.3.9 A-A*- Mitosis, Cancer & Transport

2.4 Cell Recognition & the Immune System

2.4.1 Immune System

2.4.2 The Immune Response

2.4.3 Antibodies

2.4.4 Primary & Secondary Response

2.4.5 Vaccines

2.4.7 Ethical Issues

2.4.8 End of Topic Test - Immune System

2.4.9 Exam-Style Question - Immune System

2.4.10 A-A* (AO3/4) - Immune System

3 Substance Exchange

3.1 Surface Area to Volume Ratio

3.1.1 Size & Surface Area

3.1.2 A-A* (AO3/4) - Cell Size

3.2 Gas Exchange

3.2.1 Single-Celled Organisms

3.2.2 Multicellular Organisms

3.2.3 Control of Water Loss

3.2.4 Human Gas Exchange

3.2.5 Ventilation

3.2.6 Dissection

3.2.7 Measuring Gas Exchange

3.2.8 Lung Disease

3.2.9 Lung Disease Data

3.2.10 End of Topic Test - Gas Exchange

3.2.11 A-A* (AO3/4) - Gas Exchange

3.3 Digestion & Absorption

3.3.1 Overview of Digestion

3.3.2 Digestion in Mammals

3.3.3 Absorption

3.3.4 End of Topic Test - Substance Exchange & Digestion

3.3.5 A-A* (AO3/4) - Substance Ex & Digestion

3.4 Mass Transport

3.4.1 Haemoglobin

3.4.2 Oxygen Transport

3.4.3 The Circulatory System

3.4.4 The Heart

3.4.5 Blood Vessels

3.4.6 Cardiovascular Disease

3.4.7 Heart Dissection

3.4.8 Xylem

3.4.9 Phloem

3.4.10 Investigating Plant Transport

3.4.11 End of Topic Test - Mass Transport

3.4.12 A-A* (AO3/4) - Mass Transport

4 Genetic Information & Variation

4.1 DNA, Genes & Chromosomes

4.1.2 Genes

4.1.3 A-A* (AO3/4) - DNA

4.2 DNA & Protein Synthesis

4.2.1 Protein Synthesis

4.2.2 Transcription & Translation

4.2.3 End of Topic Test - DNA, Genes & Protein Synthesis

4.2.4 Exam-Style Question - Protein Synthesis

4.2.5 A-A* (AO3/4) - Coronavirus Translation

4.2.6 A-A* (AO3/4) - Transcription

4.2.7 A-A* (AO3/4) - Translation

4.3 Mutations & Meiosis

4.3.1 Mutations

4.3.2 Meiosis

4.3.3 A-A* (AO3/4) - Meiosis

4.3.4 Meiosis vs Mitosis

4.3.5 End of Topic Test - Mutations, Meiosis

4.3.6 A-A* (AO3/4) - DNA,Genes, CellDiv & ProtSynth

4.4 Genetic Diversity & Adaptation

4.4.1 Genetic Diversity

4.4.2 Natural Selection

4.4.3 A-A* (AO3/4) - Natural Selection

4.4.4 Adaptations

4.4.5 Investigating Natural Selection

4.4.6 End of Topic Test - Genetic Diversity & Adaptation

4.4.7 A-A* (AO3/4) - Genetic Diversity & Adaptation

4.5 Species & Taxonomy

4.5.1 Classification

4.5.2 DNA Technology

4.5.3 A-A* (AO3/4) - Species & Taxonomy

4.6 Biodiversity Within a Community

4.6.1 Biodiversity

4.6.2 Agriculture

4.6.3 End of Topic Test - Species,Taxonomy& Biodiversity

4.6.4 A-A* (AO3/4) - Species,Taxon&Biodiversity

4.7 Investigating Diversity

4.7.1 Genetic Diversity

4.7.2 Quantitative Investigation

5 Energy Transfers (A2 only)

5.1 Photosynthesis

5.1.1 Overview of Photosynthesis

5.1.2 Light-Dependent Reaction

5.1.3 Light-Independent Reaction

5.1.4 A-A* (AO3/4) - Photosynthesis Reactions

5.1.5 Limiting Factors

5.1.6 Photosynthesis Experiments

5.1.7 End of Topic Test - Photosynthesis

5.1.8 A-A* (AO3/4) - Photosynthesis

5.2 Respiration

5.2.1 Overview of Respiration

5.2.2 Anaerobic Respiration

5.2.3 A-A* (AO3/4) - Anaerobic Respiration

5.2.4 Aerobic Respiration

5.2.5 Respiration Experiments

5.2.6 End of Topic Test - Respiration

5.2.7 A-A* (AO3/4) - Respiration

5.3 Energy & Ecosystems

5.3.1 Biomass

5.3.2 Production & Productivity

5.3.3 Agricultural Practices

5.4 Nutrient Cycles

5.4.1 Nitrogen Cycle

5.4.2 Phosphorous Cycle

5.4.3 Fertilisers & Eutrophication

5.4.4 End of Topic Test - Nutrient Cycles

5.4.5 A-A* (AO3/4) - Energy,Ecosystems&NutrientCycles

6 Responding to Change (A2 only)

6.1 Nervous Communication

6.1.1 Survival

6.1.2 Plant Responses

6.1.3 Animal Responses

6.1.4 Reflexes

6.1.5 End of Topic Test - Reflexes, Responses & Survival

6.1.6 Receptors

6.1.7 The Human Retina

6.1.8 Control of Heart Rate

6.1.9 End of Topic Test - Receptors, Retina & Heart Rate

6.2 Nervous Coordination

6.2.1 Neurones

6.2.2 Action Potentials

6.2.3 Speed of Transmission

6.2.4 End of Topic Test - Neurones & Action Potentials

6.2.5 Synapses

6.2.6 Types of Synapse

6.2.7 Medical Application

6.2.8 End of Topic Test - Synapses

6.2.9 A-A* (AO3/4) - Nervous Comm&Coord

6.3 Muscle Contraction

6.3.1 Skeletal Muscle

6.3.2 Sliding Filament Theory

6.3.3 Contraction

6.3.4 Slow & Fast Twitch Fibres

6.3.5 End of Topic Test - Muscles

6.3.6 A-A* (AO3/4) - Muscle Contraction

6.4 Homeostasis

6.4.1 Overview of Homeostasis

6.4.2 Blood Glucose Concentration

6.4.3 Controlling Blood Glucose Concentration

6.4.4 End of Topic Test - Blood Glucose

6.4.5 Primary & Secondary Messengers

6.4.6 Diabetes Mellitus

6.4.7 Measuring Glucose Concentration

6.4.8 Osmoregulation

6.4.9 Controlling Blood Water Potential

6.4.11 End of Topic Test - Diabetes & Osmoregulation

6.4.12 A-A* (AO3/4) - Homeostasis

7 Genetics & Ecosystems (A2 only)

7.1 Genetics

7.1.1 Key Terms in Genetics

7.1.2 Inheritance

7.1.3 Linkage

7.1.4 Multiple Alleles & Epistasis

7.1.5 Chi-Squared Test

7.1.6 End of Topic Test - Genetics

7.1.7 A-A* (AO3/4) - Genetics

7.2 Populations

7.2.1 Populations

7.2.2 Hardy-Weinberg Principle

7.3 Evolution

7.3.1 Variation

7.3.2 Natural Selection & Evolution

7.3.3 End of Topic Test - Populations & Evolution

7.3.4 Types of Selection

7.3.5 Types of Selection Summary

7.3.6 Overview of Speciation

7.3.7 Causes of Speciation

7.3.8 Diversity

7.3.9 End of Topic Test - Selection & Speciation

7.3.10 A-A* (AO3/4) - Populations & Evolution

7.4 Populations in Ecosystems

7.4.1 Overview of Ecosystems

7.4.2 Niche

7.4.3 Population Size

7.4.4 Investigating Population Size

7.4.5 End of Topic Test - Ecosystems & Population Size

7.4.6 Succession

7.4.7 Conservation

7.4.8 End of Topic Test - Succession & Conservation

7.4.9 A-A* (AO3/4) - Ecosystems

8 The Control of Gene Expression (A2 only)

8.1 Mutation

8.1.1 Mutations

8.1.2 Effects of Mutations

8.1.3 Causes of Mutations

8.2 Gene Expression

8.2.1 Stem Cells

8.2.2 Stem Cells in Disease

8.2.3 End of Topic Test - Mutation & Gene Epression

8.2.4 A-A* (AO3/4) - Mutation & Stem Cells

8.2.5 Regulating Transcription

8.2.6 Epigenetics

8.2.7 Epigenetics & Disease

8.2.8 Regulating Translation

8.2.9 Experimental Data

8.2.10 End of Topic Test - Transcription & Translation

8.2.11 Tumours

8.2.12 Correlations & Causes

8.2.13 Prevention & Treatment

8.2.14 End of Topic Test - Cancer

8.2.15 A-A* (AO3/4) - Gene Expression & Cancer

8.3 Genome Projects

8.3.1 Using Genome Projects

8.4 Gene Technology

8.4.1 Recombinant DNA

8.4.2 Producing Fragments

8.4.3 Amplification

8.4.4 End of Topic Test - Genome Project & Amplification

8.4.5 Using Recombinant DNA

8.4.6 Medical Diagnosis

8.4.7 Genetic Fingerprinting

8.4.8 End of Topic Test - Gene Technologies

8.4.9 A-A* (AO3/4) - Gene Technology

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• A-Level Biology >
• CIE A-level Biology

Enzymes: Key Concepts (A-level Biology)

Enzymes: key concepts, enzymes are involved in structural and metabolic reactions.

Enzymes are not just involved in metabolic reactions. They are also involved in formation of structural components

• Enzymes can facilitate formation of structural substances . Enzymes can help catalyse reactions that produce structural components of the organisms, such as cellulose in plants’ cell walls and collagen in animals.
• Enzymes participate in metabolic reactions. Enzymes are key in almost all metabolic reactions. Examples include cellular respiration, and digestion.

The structure of an enzyme is crucial to its function

Remember, the functionality of a protein is directly determined by its biochemical structure.

• All enzymes have an active site with a specific shape. The active site of an enzyme binds to a substrate (the target). The structure of an enzyme’s active site determines which substrates it is capable of binding to.
• Enzymes are substrate specific. Because of the unique structure of each enzyme’s active site, most enzymes can only readily bind to two substrates which “fit” into its active site.

Enzyme-Substrate Complexes

• Enzymes optimise the position of reactants . In order for chemical reactions to happen, reactants need to be in the right place at the right time, and they need to be very close to each other.
• Enzyme-substrate complexes are formed . When enzymes bind to their substrates, they form an “ enzyme-substrate complex ”. These complexes reduce activation energy in two ways:
• Bringing substrates close together . By bringing two substrates together, the enzyme puts them in very close proximity to each other thereby allowing them to readily bond with each other.
• Putting chemical strain . In catalysis (breakdown) reactions, the active site of an enzyme can put chemical strains on the bonds of a molecule causing them to break easily.

Enzyme-product Complexes

• Enzyme product complexes are formed towards the end of the reaction . Just before the reaction is complete, the substrate is changed into a product, which remains bound to the enzyme before it is released. We call this the “enzyme-product complex” .

Changes in Tertiary Structure

• Enzymes are similar to most proteins . Enzymes are proteins and therefore their chemical properties are more or less similar to most proteins. The majority of the properties that will be discussed in this section can be readily applied to proteins as well.
• Like proteins, enzymes derive their properties from their tertiary structure . Changes to their tertiary structure will lead to changes in their functionality. The tertiary structure of an enzyme determines the structure of its active site, and therefore its substrate binding ability.
• Mutations can disrupt enzymes . Mutations in the DNA of an organism can lead to the development of proteins and enzymes with mutations. These mutations can cause a protein or enzyme to lose its intended function.

Natural Degradation

• Unlike most proteins, enzymes are reusable . Once they bind to a substrate and catalyse a reaction, enzymes will release the substrate and the active site will regain its shape, ready to bind to another set of substrates. However, over time, enzymes can degrade and be replaced by new enzymes.

Enzymes are biological catalysts that are responsible for speeding up chemical reactions within cells. They are made up of proteins and are essential for many cellular processes, such as metabolism and energy production.

The function of enzymes is to lower the activation energy required for a chemical reaction to occur, making the reaction faster and more efficient. By reducing the amount of energy required for a reaction, enzymes help to keep cellular processes running smoothly and allow cells to carry out their functions.

Enzymes work by binding to specific substrate molecules and bringing them into close proximity with each other. This allows the substrate molecules to react more readily and increases the likelihood of a successful reaction. The enzyme itself remains unchanged and is able to continue catalyzing other reactions.

Enzyme activity can be influenced by several factors, including temperature, pH, and substrate concentration. Increasing the temperature can speed up enzyme activity, but if the temperature is too high, the enzyme will denature and lose its ability to function. Changes in pH can also affect enzyme activity, with each enzyme having a specific optimal pH range. The substrate concentration can also affect enzyme activity, with increasing substrate concentration leading to an increase in reaction rate.

The rate of reaction is directly proportional to the concentration of enzymes present. Increasing the number of enzymes will increase the rate of reaction, while decreasing the number of enzymes will decrease the rate of reaction. This relationship is important because it allows cells to control the speed of their reactions and to regulate their metabolic processes.

Enzymes help to lower the activation energy required for a chemical reaction to occur. By binding to substrate molecules and bringing them into close proximity, enzymes create the conditions necessary for a reaction to occur with less energy. This helps to make the reaction faster and more efficient.

Cofactors are non-protein compounds that are required for enzymes to function. Cofactors can be inorganic ions, such as iron or magnesium, or organic molecules, such as vitamins. Coenzymes are organic molecules that transfer functional groups between enzymes, and are often derived from vitamins.

The study of enzymes is important in A-Level Biology because it provides a fundamental understanding of the mechanisms behind many cellular processes. This knowledge is essential for understanding topics such as metabolism, energy production, and the regulation of cellular processes. Additionally, a deep understanding of enzymes is necessary for the development of treatments for diseases and conditions related to enzyme activity, such as genetic disorders.

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CIE 1 Cell structure

Roles of atp (a-level biology), atp as an energy source (a-level biology), the synthesis and hydrolysis of atp (a-level biology), the structure of atp (a-level biology), magnification and resolution (a-level biology), calculating cell size (a-level biology), studying cells: confocal microscopes (a-level biology), studying cells: electron microscopes (a-level biology), studying cells: light microscopes (a-level biology), life cycle and replication of viruses (a-level biology), cie 10 infectious disease, bacteria, antibiotics, and other medicines (a-level biology), pathogens and infectious diseases (a-level biology), cie 11 immunity, types of immunity and vaccinations (a-level biology), structure and function of antibodies (a-level biology), the adaptive immune response (a-level biology), introduction to the immune system (a-level biology), primary defences against pathogens (a-level biology), cie 12 energy and respiration, anaerobic respiration in mammals, plants and fungi (a-level biology), anaerobic respiration (a-level biology), oxidative phosphorylation and chemiosmosis (a-level biology), oxidative phosphorylation and the electron transport chain (a-level biology), the krebs cycle (a-level biology), the link reaction (a-level biology), the stages and products of glycolysis (a-level biology), glycolysis (a-level biology), the structure of mitochondria (a-level biology), the need for cellular respiration (a-level biology), cie 13 photosynthesis, limiting factors of photosynthesis (a-level biology), cyclic and non-cyclic phosphorylation (a-level biology), the 2 stages of photosynthesis (a-level biology), photosystems and photosynthetic pigments (a-level biology), site of photosynthesis, overview of photosynthesis (a-level biology), cie 14 homeostasis, ectotherms and endotherms (a-level biology), thermoregulation (a-level biology), plant responses to changes in the environment (a-level biology), cie 15 control and co-ordination, the nervous system (a-level biology), sources of atp during contraction (a-level biology), the ultrastructure of the sarcomere during contraction (a-level biology), the role of troponin and tropomyosin (a-level biology), the structure of myofibrils (a-level biology), slow and fast twitch muscles (a-level biology), the structure of mammalian muscles (a-level biology), how muscles allow movement (a-level biology), the neuromuscular junction (a-level biology), features of synapses (a-level biology), cie 16 inherited change, calculating genetic diversity (a-level biology), how meiosis produces variation (a-level biology), cell division by meiosis (a-level biology), importance of meiosis (a-level biology), cie 17 selection and evolution, types of selection (a-level biology), mechanism of natural selection (a-level biology), types of variation (a-level biology), cie 18 biodiversity, classification and conservation, biodiversity and gene technology (a-level biology), factors affecting biodiversity (a-level biology), biodiversity calculations (a-level biology), introducing biodiversity (a-level biology), the three domain system (a-level biology), phylogeny and classification (a-level biology), classifying organisms (a-level biology), cie 19 genetic technology, cie 2 biological molecules, properties of water (a-level biology), structure of water (a-level biology), test for lipids and proteins (a-level biology), tests for carbohydrates (a-level biology), protein structures: globular and fibrous proteins (a-level biology), protein structures: tertiary and quaternary structures (a-level biology), protein structures: primary and secondary structures (a-level biology), protein formation (a-level biology), proteins and amino acids: an introduction (a-level biology), phospholipid bilayer (a-level biology), cie 3 enzymes, enzymes: inhibitors (a-level biology), enzymes: rates of reaction (a-level biology), enzymes: intracellular and extracellular forms (a-level biology), enzymes: mechanism of action (a-level biology), enzymes: introduction (a-level biology), cie 4 cell membranes and transport, transport across membranes: active transport (a-level biology), investigating transport across membranes (a-level biology), transport across membranes: osmosis (a-level biology), transport across membranes: diffusion (a-level biology), signalling across cell membranes (a-level biology), function of cell membrane (a-level biology), factors affecting cell membrane structure (a-level biology), structure of cell membranes (a-level biology), cie 5 the mitotic cell cycle, chromosome mutations (a-level biology), cell division: checkpoints and mutations (a-level biology), cell division: phases of mitosis (a-level biology), cell division: the cell cycle (a-level biology), cell division: chromosomes (a-level biology), cie 6 nucleic acids and protein synthesis, transfer rna (a-level biology), transcription (a-level biology), messenger rna (a-level biology), introducing the genetic code (a-level biology), genes and protein synthesis (a-level biology), synthesising proteins from dna (a-level biology), structure of rna (a-level biology), dna replication (a-level biology), dna structure and the double helix (a-level biology), polynucleotides (a-level biology), cie 7 transport in plants, translocation and evidence of the mass flow hypothesis (a-level biology), the phloem (a-level biology), importance of and evidence for transpiration (a-level biology), introduction to transpiration (a-level biology), the pathway and movement of water into the roots and xylem (a-level biology), the xylem (a-level biology), cie 8 transport in mammals, controlling heart rate (a-level biology), structure of the heart (a-level biology), transport of carbon dioxide (a-level biology), transport of oxygen (a-level biology), exchange in capillaries (a-level biology), structure and function of blood vessels (a-level biology), cie 9 gas exchange and smoking, lung disease (a-level biology), pulmonary ventilation rate (a-level biology), ventilation (a-level biology), structure of the lungs (a-level biology), general features of exchange surfaces (a-level biology), understanding surface area to volume ratio (a-level biology), the need for exchange surfaces (a-level biology), edexcel a 1: lifestyle, health and risk, phospholipids – introduction (a-level biology), edexcel a 2: genes and health, features of the genetic code (a-level biology), gas exchange in plants (a-level biology), gas exchange in insects (a-level biology), edexcel a 3: voice of the genome, edexcel a 4: biodiversity and natural resources, edexcel a 5: on the wild side, reducing biomass loss (a-level biology), sources of biomass loss (a-level biology), transfer of biomass (a-level biology), measuring biomass (a-level biology), net primary production (a-level biology), gross primary production (a-level biology), trophic levels (a-level biology), edexcel a 6: immunity, infection & forensics, microbial techniques (a-level biology), the innate immune response (a-level biology), edexcel a 7: run for your life, edexcel a 8: grey matter, inhibitory synapses (a-level biology), synaptic transmission (a-level biology), the structure of the synapse (a-level biology), factors affecting the speed of transmission (a-level biology), myelination (a-level biology), the refractory period (a-level biology), all or nothing principle (a-level biology), edexcel b 1: biological molecules, inorganic ions (a-level biology), edexcel b 10: ecosystems, nitrogen cycle: nitrification and denitrification (a-level biology), the phosphorus cycle (a-level biology), nitrogen cycle: fixation and ammonification (a-level biology), introduction to nutrient cycles (a-level biology), edexcel b 2: cells, viruses, reproduction, edexcel b 3: classification & biodiversity, edexcel b 4: exchange and transport, edexcel b 5: energy for biological processes, edexcel b 6: microbiology and pathogens, edexcel b 7: modern genetics, edexcel b 8: origins of genetic variation, edexcel b 9: control systems, ocr 2.1.1 cell structure, structure of prokaryotic cells (a-level biology), eukaryotic cells: comparing plant and animal cells (a-level biology), eukaryotic cells: plant cell organelles (a-level biology), eukaryotic cells: the endoplasmic reticulum (a-level biology), eukaryotic cells: the golgi apparatus and lysosomes (a-level biology), ocr 2.1.2 biological molecules, introduction to eukaryotic cells and organelles (a-level biology), ocr 2.1.3 nucleotides and nucleic acids, ocr 2.1.4 enzymes, ocr 2.1.5 biological membranes, ocr 2.1.6 cell division, diversity & organisation, ocr 3.1.1 exchange surfaces, ocr 3.1.2 transport in animals, ocr 3.1.3 transport in plants, examples of xerophytes (a-level biology), introduction to xerophytes (a-level biology), ocr 4.1.1 communicable diseases, structure of viruses (a-level biology), ocr 4.2.1 biodiversity, ocr 4.2.2 classification and evolution, ocr 5.1.1 communication and homeostasis, the resting potential (a-level biology), ocr 5.1.2 excretion, ocr 5.1.3 neuronal communication, hyperpolarisation and transmission of the action potential (a-level biology), depolarisation and repolarisation in the action potential (a-level biology), ocr 5.1.4 hormonal communication, ocr 5.1.5 plant and animal responses, ocr 5.2.1 photosynthesis, ocr 5.2.2 respiration, ocr 6.1.1 cellular control, ocr 6.1.2 patterns of inheritance, ocr 6.1.3 manipulating genomes, ocr 6.2.1 cloning and biotechnology, ocr 6.3.1 ecosystems, ocr 6.3.2 populations and sustainability.

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A-Level AQA Biology - Biological Molecules

Structure & function.

What are some of the key terms associated with enzymes?

• Active site
• Enzyme-substrate complex
• Biological catalyst

Enzymes are biological catalysts made of proteins. They speed up reactions without being used up themselves. Some of the essential reactions they catalyze include respiration, photosynthesis, protein synthesis, and digestion. Having studied the structure and function of proteins, this theory can now be applied to enzymes. While enzymes are relatively large molecules, only a small part of the enzymes attaches to a substrate to catalyze a reaction. This site is known as the active site. The active site is specific and unique in shape due to the specific folding and bonding in the tertiary structure of the protein. Due to this specific active site, enzymes can only attach to substrates that are complementary in shape.

Two Models of Enzyme Action

We have stated above the structure and function of enzymes, and next is to explain how enzymes speed up reactions by attaching to substrates. All reactions require a certain amount of energy before they occur (diagram a), this is known as the activation energy. When enzymes attach to the substrate, they can lower the activation energy needed for the reaction to occur (diagram b), and therefore speed up the reaction. There are two models to explain how this occurs.

Lock & Key Model

This model suggests that the enzyme is like a lock and that the substrate is like a key that fits into it due to their complementarity in shape. This model suggests that the enzyme active site is a fixed shape and that due to random collision, the substrate can collide and attach to the enzyme. This forms an enzyme-substrate complex.

The term enzyme-substrate complex is always a marking point for enzyme questions!

Once the enzyme-substrate complex has formed, the charged groups within the active site are thought to distort the substrate and therefore lower the activation energy. The products are then released, and the enzyme active site is empty and ready to be reused.

Induced Fit Model

This model suggests that the enzyme is like a glove and the substrate is like your hand; the empty glove is not exactly complementary in shape to your hand, but when your hand enters it enables the glove to mold around your hand to become completely complementary. This analogy describes the process well. The induced fit is when the enzyme active site is induced, or slightly changes shape, to mold around the substrate. When the enzyme-substrate complex occurs, due to the enzyme molding around the substrate, it puts strain on the bonds and therefore lowers the activation energy. The products are then removed, and the enzyme active site returns to its original shape. The induced fit model is the accepted model for how enzymes function.

In summary, what is the difference between the two models? The induced fit model suggests that the active site changes shape and then becomes complementary in shape, whereas the lock and key model suggests enzymes are a fixed shape, and the active site does not change.

Factors Affecting Enzymes

Enzymes, which are proteins, are sensitive to certain conditions:

Temperature

If the temperature is too low, there is not enough kinetic energy for successful collisions. If the temperature is too high, enzymes denature, the active site changes shape, and enzyme-complexes cannot form.

Too high or too low a pH will interfere with the charges in the amino acids in the active site. Therefore the enzyme denatures.

Substrate and Enzyme Concentration

If there is not enough substrate added, then the reaction will be slower as there will be fewer collisions between the enzyme and substrate. If there are not enough enzymes, then the enzyme active sites will become saturated with substrate and unable to work any faster.

Enzyme Inhibitors

Competitive inhibitors are the same shape as the substrate and can bind to the active site. This prevents the substrate from binding, and the reaction occurring. If you add more substrate, this will flood/out-compete the inhibitor, knocking them out of the active site.

Non-competitive inhibitors bind to the enzyme away from the active site, the allosteric site. This causes the active site to change shape, and therefore the substrate can no longer bind, regardless of how much substrate is added (see graph below):

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Aqa alevel biology 25 mark essay - interactions between cells and organisms

Subject: Biology

Age range: 16+

Resource type: Other

Last updated

24 March 2024

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