a level biology essay on enzymes

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 Revision Notes >
• CIE A-level Biology Revision Notes

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” .
• Most enzyme reactions are reversible . The importance of the enzyme-product complex is that in most cases, the enzyme could induce the product to change back into the substrate, i.e. reverse the reaction. This is why most reactions catalysed by an enzyme are reversible.

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, related links.

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Properties of the enzyme

The relationship between temperature and enzyme activity, what is an enzyme, what is the structure of enzymes, what are the factors affecting the activity of enzymes, what happens to enzymes at high temperatures.

Enzymes are biological catalysts that accelerate chemical reactions in living organisms by lowering the activation energy required for a reaction to occur, and are essential for maintaining cellular processes such as metabolism, DNA replication, and protein synthesis. Keep reading for more detailed A-level Biology revision!

• Biochemical reactions are necessary for growth, repairing damaged tissues and obtaining energy and take place in all living organisms’ bodies. These reactions are called ‘metabolism’ and happen continuously. If they stop working, it leads to the death of the organism.
• Metabolism is a group of biochemical processes that take place inside a cell. In these processes, complex and macromolecules are built from simple molecules. This is called anabolism. On the other hand, some molecules get broken down to extract chemical energy stored in them. This is called catabolism.
• Catabolism is the process of releasing energy stored in the chemical bonds present in the molecules, such as glucose. In the process of anabolism, simple molecules are used to build up more complex substances through a chain of reactions. These reactions consume energy, such as the synthesis of proteins from amino acids.
• All the reactions occurring in living organisms require high activation energy to take place. To reduce the cell’s consumption of energy, there should be a catalyst to ensure that the chemical reaction occurs rapidly throughout, reducing the activation energy. This catalyst is the enzymes.
• Enzymes are biological catalysts made up of large protein molecules. They speed up the chemical reactions inside the cell. The enzyme is made up of a combination of amino acids forming a chain or polypeptide between each other.

Read more about Enzyme Mechanism of Action

• Enzymes are similar to the other chemical catalysts. They participate in the reaction without getting affected. In other words, they speed up the chemical reactions inside the cells without getting consumed.
• Enzymes are affected by the hydrogen ion concentration (pH) and the temperature.
• Enzymes are much more specific than other catalysts. Each enzyme is specialized for one reactant substance. This reactant substance is called substrate, and it is specialized for one type of reaction or for a few reactions.
• There are several factors that affect the speed of enzymes, such as the concentration of the enzyme, the concentration of the substrate, temperature, hydrogen ion concentration (pH), and the presence of inhibitors.

The following is an illustration to show the effect of some of these factors on the speed of enzyme action.

• The protein nature of the enzymes makes them extremely sensitive to thermal changes. Enzyme activity is determined by a narrow range of temperatures compared to ordinary chemical reactions.
• Each enzyme has a certain temperature at which it is more active. This point is called the ‘optimal temperature’, which ranges between 37 to 40C°.
• The enzyme activity gradually lowers as the temperature rises more than the optimal temperature until it reaches a certain temperature at which the enzyme activity stops completely due to the change of its natural composition.

Potential of hydrogen (pH)

• Potential of hydrogen (pH) is the best measurement for determining the concentration of hydrogen ion H + in the solution. It also determines whether the liquid is acidic, basic or neutral. Generally, all liquids with a pH below 7 are called acids, whereas the liquids with a pH above 7 are called bases or alkaline. Liquids with pH 7 are neutral and equal the acidity of pure water at 25°C. You can determine the pH of any solution using the pH indicator scale.
• Enzymes are protein substances. They contain acidic carboxylic groups (COOH), and basic amino groups (NH 2) . Enzymes are affected by the changing of pH value.
• Each enzyme has a pH value at which it works with maximum efficiency called the optimal pH. If the pH is lower or higher than the optimal pH, the enzyme activity decreases until it stops working. For example, pepsin works at a low pH, i.e, it is highly acidic, while trypsin works at a high pH. i.e, it is basic. Most enzymes work at neutral pH 7.4.

Frequently Asked Questions

An enzyme is a biocatalyst. It means that enzymes help in the regulation of chemical reactions taking place in human bodies.

Enzymes are globular proteins in structure. Enzymes are folded on themselves to form a globular structure.

The activity of enzymes is affected by the following factors:

Enzyme concentration

Substrate concentration

Temperature

Enzymes have an optimal temperature at which they work. Temperature higher than optimal temperature denatures the enzymes.

• Biological Molecules

Enzymes are Biological Catalysts . They increase the rate of Metabolic reactions . Almost all Biological Reactions involve Enzymes. All enzymes are Globular Proteins with a specific Tertiary Shape . They are usually specific to only one reaction.

The part of the Enzyme that acts a Catalyst is called the Active Site . The rest of the Enzyme is much larger and is involved in maintaining the specific shape of of the Enzyme.

When a reaction involving an Enzyme occurs, a Substrate is turned into a Product . The Substrate can be one or more molecules. The Active Site of an Enzyme is Complementary to the Substrate it catalyses.

• Lactase : Breaks down Lactose into Glucose and Galactose.
• Catalase : Breaks Hydrogen Peroxide down into Water and Oxygen.
• Glycogen Synthase : Catalyses the formation of Glycosidic Bonds between Glucose molecules.
• ATP-ase : Breaks down ATP into ADP, producing energy._

Enzymes in the Real World

Since Enzymes are Proteins, which are effected by their environment , organisms that live in varying conditions have adapted by producing Enzymes more suitable to their environments. Endotherms (animals that maintain their body temperature) keep the temperature of the Enzymes within their bodies constant to ensure optimum rates of reaction .

Enzymes are used for a wide variety of purposes, such as in digestion . The action of an Enzyme may be Intracellular (the Enzymes are attached to the cell membrane or are in the Cytoplasm , and reactions occur inside the cell) or Extracellular (Enzymes work outside cells , and their products may be absorbed into the cell)

Enzymes are also used in protection against Pathogens . They can be used to destroy invading Microorgansims. For example, Phagocytes engulf Pathogens and the Endocytosed Vesicle then fuses with Lysosomes which contain enzymes that destroy the Pathogen’s cell membrane.

How Enzymes Work

• Most reactions in a cell require very high temperatures to get going, which would destroy the cell. Enzymes work by lowering the Activation Energy of a reaction.
• The Activation Energy of a reaction is lowered by putting stress on the bonds within a molecule, or by holding molecules close together. This increases the likelihood of a reaction, and so lowers the energy required to begin it.

The Lock-and-key Hypothesis

The Lock-and-key Hypothesis is a model of how Enzymes catalyse Substrate reactions. It states that the shape of the Active Sites of Enzymes are exactly Complementary to the shape of the Substrate.

When a substrate molecule collides with an enzyme whose Active Site shape is complementary, the substrate will fit into the Active Site and an Enzyme-Substrate Complex will form.

• The enzyme will catalyse the reaction, and the products , together with the enzyme, will form an Enzyme-Product Complex . According to this model, it is possible for an enzyme to catalyse a reverse reaction.

The Induced-Fit Hypothesis

A more recent model, which is backed up by evidence ,and is widely accepted as describing the way enzymes work, is the Induced-Fit Hypothesis . It states that the shape of Active Sites are not exactly Complementary , but change shape in the presence of a specific substrate to become Complementary .

When a substrate molecule collides with an enzyme, if its composition is specifically correct, the shape of the enzyme’s Active Site will change so that the substrate fits into it and an Enzyme-Substrate Complex can form. The reaction is then catalysed and an Enzyme-Product Complex forms.

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New A-level biology example essay: The importance of enzymes in the functioning of cells, tissues an

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Proteins: Enzymes ( AQA A Level Biology )

Topic questions.

Explain why enzymes are referred to as biological catalysts . 

How did you do?

Figure 1 below shows a representation of an enzyme-controlled reaction.

Describe the events taking place in Figure 1 .

Figure 1 shows a model of enzyme action called the lock and key model. Modern understanding of enzyme function uses a modified version of this model called the induced fit hypothesis. State the difference between the lock and key model and the induced fit hypothesis. You may use a diagram in your answer. 

Figure 2 below shows how enzymes affect biological reactions.

Use Figure 2 and/or your own knowledge of enzyme function to explain how enzymes  function as biological catalysts. 

Did this page help you?

A student wanted to investigate the effect of substrate concentration on the activity of an enzyme called catalase. Catalase is an enzyme that commonly occurs inside living cells where it breaks down toxic hydrogen peroxide into oxygen and water. Figure 1 below shows the experiment set up by the student.

Give two control variables that the student would need to be aware of in the experiment shown in Figure 1 .

The student decided to make up solutions at five different hydrogen peroxide concentrations. Their measurements for these solutions are shown in Table 1 below.

Give the measurements needed to fill in gaps A-C in Table 1 .

After measuring out the range of hydrogen peroxide concentrations shown in Table 1 , the student carried out the experiment using the equipment set up in Figure 1 . They recorded the volume of oxygen (the product) produced after one minute, and repeated this measurement 3 times at each concentration. Their results are shown in Table 2 .

Use the data in Table 2 to calculate the value missing from the square marked X .

Plot a graph of hydrogen peroxide concentration against the mean volume of oxygen.

A student wanted to investigate the effect of temperature on the activity of the enzyme  amylase. They decided to follow the procedure in Figure 1 below.

State the purpose of the iodine solution in the spotting tiles, and how it achieves this  purpose.

Figure 1 below shows the results gained for the experiment carried out at 10°C.

Explain why the iodine no longer chages colour at 300 seconds in Figure 1.

Table 1 shows the results gained by the student.

Explain the results shown at 50°C and 60°C in Table 1 . 

State how the student could make their results more precise .

Figure 1 shows how the addition of a molecule named here as molecule X affects the  rate of an enzyme-controlled reaction. 

Describe how the addition of molecule X affects the rate of reaction in Figure 1 .

Figure 2 shows how molecule X interacts with the enzyme. 

Use Figure 2 to explain the results shown in Figure 1 . 

Figure 3 below shows another molecule, molecule Y . 

Suggest how molecule Y in Figure 3 might interact with the enzyme shown in Figure 2 .

Sketch a line on Figure 1 to show how molecule Y might affect the rate of reaction.

A researcher investigated the effect of pH on the activity of stomach enzyme pepsin.  Their results are shown in Figure 1 below. 

Calculate the rate of reaction at pH 4. Give your answer with the correct units.

Describe the differences between the curves at pH 4 and pH 2.

State why product production at pH 2 does not continue indefinitely but reaches a  plateau at around 14.75 g.

Predict and explain what the graph might show if the pH were to be raised to pH 10.

Enzyme X is found in human cells. It has been discovered that there are non-functional and functional forms of enzyme   X that exist. The functional form of enzyme X is only formed when a phosphate group binds to enzyme X . The mechanism described is shown in Figure 1 below.

Explain how the addition of a phosphate group to the non-functional form of enzyme X leads to the formation of the functional form of enzyme X .

The formation of the enzyme-substrate complex between the functional form of enzyme X and its substrate results in products that affect the renewal of skin cells. Too high a concentration of the products results in excess skin renewal. A chronic skin disease is caused by an abnormal form of enzyme X . Figure 2 shows the abnormal form of enzyme X .

Suggest how the abnormal enzyme X causes the chronic skin disease.

Drug Y is a drug used to treat the chronic skin condition caused by abnormal enzyme X . Figure 3 shows how drug Y inhibits abnormal enzyme X .

Using the information given, describe how drug Y prevents the development of the chronic skin condition.

Individuals that are prescribed drug Y must take the drug at regular, repeated intervals. It is also vital that they do not exceed the maximum prescribed dose. Explain why.

A protease is an enzyme that digests protein. A research scientist isolated protease C from a particular species of bacteria. They investigated the effect of temperature on the rate of hydrolysis of a protein by protease C .  After 4 minutes the mass of protein hydrolysed was measured at each temperature. The results can be seen in Table 1 below.

Fill in the missing details of Table 1 .

Plot a graph of the results seen in Table 1 .

A research assistant concluded from their graph of the data in Table 1 that the bacterium's habitat was likely around 25°C. Evaluate this conclusion.

Suggest how the research scientist controlled the pH throughout the experiment.

In their first few weeks of life puppies produce large amounts of the enzyme lactase so that they can break down their mothers milk. However as they grow older and are weaned onto solid dog food they produce less and less lactase. Milk can still be beneficial for an older puppy because of its high calcium content. 

Cow’s milk contains large amounts of the sugar lactose but it can be made suitable for older puppies via treatment with the enzyme lactase. This makes the cow’s milk lactose-free. Beads are coated with the enzyme lactase and placed in a glass cylinder, as shown in Figure 1 below. As the cow’s milk flows over the beads the lactose is hydrolysed.

Lactose is broken down into glucose and galactose by lactase. Galactose has a similar structure to a section of the lactose molecule. Explain how galactose acts as an inhibitor of lactase.

Attaching the enzyme to the beads is a more efficient method for using the enzyme, rather than directly adding it to cow’s milk. Suggest four reasons why it is a more efficient method.

The scientist varied the flow rate of the milk through the column. The effect of flow rate on the concentration of glucose in Milk B is shown in Table 1 below.

Using the information from Table 1 suggest which flow rate should be used by a manufacturer wanting to produce large volumes of lactose free puppy milk. Justify your answer.

Many humans also struggle with digesting cow’s milk. Those who are lactose intolerant have little or no lactase enzymes.

Fortunately, lactase tablets can be taken to help aid in the digestion of lactose heavy foods. These tablets don’t have to be stored at a lower temperature but other enzymes used in experiments can often require storage in a laboratory refrigerator. Use your knowledge of protein structure to explain why this is so.

An enzyme can only catalyse one reaction but a substrate can be hydrolysed by more than one enzyme. Explain why.

A lab technician was investigating the effect of temperature on the rate of an specific enzyme-controlled reaction.  Water baths were used to maintain temperatures of 30 and 50 degrees Celsius. For the reactions at both temperatures, the same concentration of substrate and enzyme was used. Figure 1 shows their results.

Sketch tangents to find the initial rates of reaction for both temperatures. Then use these values to calculate the ratio of the initial rates of reaction at 50°C : 30°C. Show your working.

Ratio = _________:1

Explain the difference in the initial rates of reaction at 50 °C and 30 °C.

Explain the difference in the rates of reaction at 50 °C and 30 °C after 10 minutes.

Scientists investigated the effect of pH on the activity of enzyme A . Agar plates containing the enzyme substrate were used. The substrate caused the agar to go a grey colour. The scientists created four wells of equal size in the agar of each plate. A drop of enzyme A solution was added to each of the wells. The pH of the enzyme solution was different in each well. The agar plates were incubated for 5 hours at a constant temperature.  

Figure 1 below shows how the agar plates looked after they were incubated. 

Describe and explain the results seen in Figure 1 .

While the scientists were investigating another enzyme, enzyme B , they found that a change in pH from 7.2 to 7.6 had a very large effect on the rate of reaction controlled by enzyme B . Using your knowledge of pH, explain why a small change in pH produces a large effect on the rate of reaction.

Research scientists have investigated the effects of both competitive and non-competitive inhibitors of enzyme A .  One of the inhibitors being investigated is represented  in Figure 2 below. State what type of inhibitor molecule 1 is and describe how it works.

Suggest how the inhibition of enzyme A by molecule 1 could be overcome.

Enzymes are known to reduce the activation energy of biochemical reactions. Suggest and explain two mechanisms by which activation energy might be lowered. Use the context of an anabolic reaction, i.e. two small substrates being joined chemically into a larger product.   

Explain the Induced Fit Hypothesis which has superseded the previous model of enzyme action, the Lock and Key Hypothesis.

The first step of cellular respiration is the phosphorylation of glucose in the cell  cytoplasm.  This is catalysed by the enzyme hexokinase:

glucose + ATP → glucose 6-phosphate + ADP 

Figure 1 shows the images obtained of the enzyme and enzyme-substrate  complex. X-ray crystallography was used to obtain these images.

Identify the evidence of the induced fit hypothesis in Figure 1 .

Describe and explain two ways in which an enzyme can become denatured.

Certain plants that reproduce sexually contain an enzyme called pyrophosphatase. This enzyme plays a role in ensuring self-incompatibility, which is a mechanism that prevents a plant from fertilising itself. The selective advantage of self-incompatibility is that more cross-breeding can occur within a species, which has long term benefits for evolution and for maintaining a wide pool of alleles.

Known volumes of pyrophosphatase and substrate can be mixed in a cuvette with a blue dye that starts as colourless and develops colour over time. The rate of colour development can be measured in a colorimeter by measuring the absorbance of light of wavelength 620 nm (red light). 

Figure 1 shows the mean rate of reaction of pyrophosphatase measured over five repeats at 20°C.

State why the wavelength of 620 nm is selected for this experimental measurement.

Use Figure 1 to calculate the rate of the reaction at 100 seconds. Give your answer in suitable units. 

Predict and explain whether your answer to 2 (b) would be higher, lower or the same if a higher concentration of enzyme at the beginning of the experiment.

As temperature increases, the rate at which pyrophosphatase works increases, then decreases.  Explain why these changes take place.  

Describe and explain the similarities and differences between competitive and non-competitive enzyme inhibition. 

Many products of multi-step cellular reactions act as inhibitors of the enzymes that catalyse the preceding steps in a metabolic pathway. For example, ATP acts as a non-competitive inhibitor of the enzyme pyruvate kinase, which catalyses the final step  of glycolysis, the first stage of cellular respiration of glucose. 

Suggest how the inhibition of pyruvate kinase by ATP allows cells to prevent overproduction and wasting of cellular energy.

Figure 1 shows the effects of increasing substrate concentration on enzyme activity with and without two types of inhibitor, competitive and non-competitive. 

Sketch a line on both graphs to indicate the effect of increasing inhibitor concentration in each case. Explain the position and shape of each line. 

Compare and contrast the features of a substrate and a competitive inhibitor

Define the term ‘specificity’ in the context of enzymes. 

In humans, the enzyme sucrase hydrolyses sucrose. This reaction occurs in the small intestine at 37°C. Explain why sucrase only hydrolyses sucrose, and why this reaction can take place at normal body temperature. 

A sucrose solution was split into two equal portions. One portion ( A ) was left untreated at room temperature, and the other ( B ) was treated with sucrase and left for 30 minutes at room temperature. Both solutions were tasted by human volunteers. Identify which solution would taste sweeter and explain your choice.

Suggest two sources of error that could arise from an experiment to measure the effect of temperature on the rate of an enzyme-controlled reaction. Assume that in this experiment, the dependent variable is measured as the volume of a gas produced.

A significant amount of research has been conducted on the enzyme composition of extremophile microorganisms, in order to discover new enzymes that can be used in the home in extreme conditions. One such organism, Planococcus halocryophilus , is a psychrophile (it grows at cold temperatures around 0°C). Trials with the enzymes of P. halocryophilus have discovered applications of these enzymes in the detergent industry. 

Suggest and explain how these trial results are encouraging for the laundry detergent industry.  

Many commercially-produced biological laundry detergents contain a range of different enzymes. Explain why a range of enzymes can improve the detergent’s performance in the home.

Papain is a proteolytic enzyme derived from papaya fruit. It has been used in contact lens cleaning solutions to remove denatured protein-containing deposits that accumulate on the surfaces of contact lenses during long periods of wear. The periodic removal of protein deposits increase wearer comfort and extends wearing time.

Th e principal protein component of tear film fluid is lysozyme. Suggest a reason for the presence of lysozyme in tear film fluid.  

Lysozyme and other proteins present in tear film fluid can denature rapidly when in contact with contact lens material. This denatured material loses its original function and forms deposits on the lens surface. Describe and explain the mode of action of papain against the denatured protein deposits on the surfaces of the contact lenses.

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Chicken meal as a fishmeal substitute: effects on growth, antioxidants, and digestive enzymes in lithobates catesbeianus, simple summary, 1. introduction, 2. materials and methods, 2.1. experimental feed, 2.2. animals and feeding management, 2.3. sample collection, 2.4. sample analysis, detection, and calculation, 2.5. statistical analysis of data, 3.1. effect of replacing fishmeal with chicken meal on the growth performance of bullfrogs, 3.2. the effect of chicken meal replacing fishmeal on the amino acid composition of muscle, 3.3. the effect of chicken meal replacing fishmeal on the antioxidant capacity of bullfrog muscles, 3.4. effect of chicken meal replacing fishmeal on the intestinal tissue structure and digestive enzyme activity of bullfrogs, 3.5. the effect of replacing fishmeal with chicken meal on the antioxidant capacity and inflammatory indicators in the intestine of bullfrogs, 4. discussion, 5. conclusions, supplementary materials, author contributions, institutional review board statement, informed consent statement, data availability statement, conflicts of interest.

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Zhu, B.; Xu, W.; Dai, Z.; Shao, C.; Hu, Y.; Chen, K. Chicken Meal as a Fishmeal Substitute: Effects on Growth, Antioxidants, and Digestive Enzymes in Lithobates catesbeianus . Animals 2024 , 14 , 2200. https://doi.org/10.3390/ani14152200

Zhu B, Xu W, Dai Z, Shao C, Hu Y, Chen K. Chicken Meal as a Fishmeal Substitute: Effects on Growth, Antioxidants, and Digestive Enzymes in Lithobates catesbeianus . Animals . 2024; 14(15):2200. https://doi.org/10.3390/ani14152200

Zhu, Bo, Wenjie Xu, Zhenyan Dai, Chuang Shao, Yi Hu, and Kaijian Chen. 2024. "Chicken Meal as a Fishmeal Substitute: Effects on Growth, Antioxidants, and Digestive Enzymes in Lithobates catesbeianus " Animals 14, no. 15: 2200. https://doi.org/10.3390/ani14152200

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