1.4.5
Enzymes
Enzymes
Enzymes
Enzymes are proteins that catalyse reactions. The chemical reactants that enzymes bind to are called substrates.
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Biological catalyst
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.
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Activation energy
Activation energy
- For a chemical reaction to start, it needs a specific amount of energy. This amount of energy is different for different reactions.
- This is called the activation energy.
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Activation energy and enzymes
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.
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The active site
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
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.
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The lock and key model
The lock and key model
- The lock and key model was originally used to explain enzyme action.
- The model proposes that the enzyme and substrate fit together perfectly.
- The substrate is a key fitting into a lock (the enzyme).
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The induced fit model
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
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:
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Active site
Active site
- Every enzyme only catalyses one specific reaction.
- Every enzyme has a specific active site that is complementary to the specific substrate.
- This jigsaw puzzle-like match between an enzyme and its substrates is what makes enzymes highly specific.
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Environmental factors
Environmental factors
- The 3D, tertiary structure of the polypetide chain determines the shape of the active site.
- Environmental changes can change the tertiary structure of the active site and can stop the enzyme from working properly.
- This is called a denatured enzyme.
1Biological Molecules
1.1Monomers & Polymers
1.2Carbohydrates
1.3Lipids
1.4Proteins
1.4.1The Peptide Chain
1.4.2Investigating Proteins
1.4.3Primary & Secondary Protein Structure
1.4.4Tertiary & Quaternary Protein Structure
1.4.5Enzymes
1.4.6Factors Affecting Enzyme Activity
1.4.7Enzyme-Controlled Reactions
1.4.8End of Topic Test - Lipids & Proteins
1.4.9A-A* (AO3/4) - Enzymes
1.4.10A-A* (AO3/4) - Proteins
1.5Nucleic Acids
1.6ATP
1.7Water
1.8Inorganic Ions
2Cells
2.1Cell Structure
2.2Mitosis & Cancer
2.3Transport Across Cell Membrane
2.4Cell Recognition & the Immune System
3Substance Exchange
3.1Surface Area to Volume Ratio
3.2Gas Exchange
3.3Digestion & Absorption
4Genetic Information & Variation
4.1DNA, Genes & Chromosomes
4.2DNA & Protein Synthesis
4.3Mutations & Meiosis
4.4Genetic Diversity & Adaptation
4.5Species & Taxonomy
4.6Biodiversity Within a Community
4.7Investigating Diversity
5Energy Transfers (A2 only)
5.1Photosynthesis
5.1.1Overview of Photosynthesis
5.1.2Photoionisation of Chlorophyll
5.1.3Production of ATP & Reduced NADP
5.1.4Cyclic Photophosphorylation
5.1.5Light-Independent Reaction
5.1.6A-A* (AO3/4) - Photosynthesis Reactions
5.1.7Limiting Factors
5.1.8Photosynthesis Experiments
5.1.9End of Topic Test - Photosynthesis
5.1.10A-A* (AO3/4) - Photosynthesis
5.2Respiration
5.3Energy & Ecosystems
6Responding to Change (A2 only)
6.1Nervous Communication
6.2Nervous Coordination
6.3Muscle Contraction
6.4Homeostasis
6.4.1Overview of Homeostasis
6.4.2Blood Glucose Concentration
6.4.3Controlling Blood Glucose Concentration
6.4.4End of Topic Test - Blood Glucose
6.4.5Primary & Secondary Messengers
6.4.6Diabetes Mellitus
6.4.7Measuring Glucose Concentration
6.4.8Osmoregulation
6.4.9Controlling Blood Water Potential
6.4.10ADH
6.4.11End of Topic Test - Diabetes & Osmoregulation
6.4.12A-A* (AO3/4) - Homeostasis
7Genetics & Ecosystems (A2 only)
7.1Genetics
7.2Populations
7.3Evolution
7.3.1Variation
7.3.2Natural Selection & Evolution
7.3.3End of Topic Test - Populations & Evolution
7.3.4Types of Selection
7.3.5Types of Selection Summary
7.3.6Overview of Speciation
7.3.7Causes of Speciation
7.3.8Diversity
7.3.9End of Topic Test - Selection & Speciation
7.3.10A-A* (AO3/4) - Populations & Evolution
8The Control of Gene Expression (A2 only)
8.2Gene Expression
8.2.1Stem Cells
8.2.2Stem Cells in Disease
8.2.3End of Topic Test - Mutation & Gene Epression
8.2.4A-A* (AO3/4) - Mutation & Stem Cells
8.2.5Regulating Transcription
8.2.6Epigenetics
8.2.7Epigenetics & Disease
8.2.8Regulating Translation
8.2.9Experimental Data
8.2.10End of Topic Test - Transcription & Translation
8.2.11Tumours
8.2.12Correlations & Causes
8.2.13Prevention & Treatment
8.2.14End of Topic Test - Cancer
8.2.15A-A* (AO3/4) - Gene Expression & Cancer
8.3Genome Projects
Jump to other topics
1Biological Molecules
1.1Monomers & Polymers
1.2Carbohydrates
1.3Lipids
1.4Proteins
1.4.1The Peptide Chain
1.4.2Investigating Proteins
1.4.3Primary & Secondary Protein Structure
1.4.4Tertiary & Quaternary Protein Structure
1.4.5Enzymes
1.4.6Factors Affecting Enzyme Activity
1.4.7Enzyme-Controlled Reactions
1.4.8End of Topic Test - Lipids & Proteins
1.4.9A-A* (AO3/4) - Enzymes
1.4.10A-A* (AO3/4) - Proteins
1.5Nucleic Acids
1.6ATP
1.7Water
1.8Inorganic Ions
2Cells
2.1Cell Structure
2.2Mitosis & Cancer
2.3Transport Across Cell Membrane
2.4Cell Recognition & the Immune System
3Substance Exchange
3.1Surface Area to Volume Ratio
3.2Gas Exchange
3.3Digestion & Absorption
4Genetic Information & Variation
4.1DNA, Genes & Chromosomes
4.2DNA & Protein Synthesis
4.3Mutations & Meiosis
4.4Genetic Diversity & Adaptation
4.5Species & Taxonomy
4.6Biodiversity Within a Community
4.7Investigating Diversity
5Energy Transfers (A2 only)
5.1Photosynthesis
5.1.1Overview of Photosynthesis
5.1.2Photoionisation of Chlorophyll
5.1.3Production of ATP & Reduced NADP
5.1.4Cyclic Photophosphorylation
5.1.5Light-Independent Reaction
5.1.6A-A* (AO3/4) - Photosynthesis Reactions
5.1.7Limiting Factors
5.1.8Photosynthesis Experiments
5.1.9End of Topic Test - Photosynthesis
5.1.10A-A* (AO3/4) - Photosynthesis
5.2Respiration
5.3Energy & Ecosystems
6Responding to Change (A2 only)
6.1Nervous Communication
6.2Nervous Coordination
6.3Muscle Contraction
6.4Homeostasis
6.4.1Overview of Homeostasis
6.4.2Blood Glucose Concentration
6.4.3Controlling Blood Glucose Concentration
6.4.4End of Topic Test - Blood Glucose
6.4.5Primary & Secondary Messengers
6.4.6Diabetes Mellitus
6.4.7Measuring Glucose Concentration
6.4.8Osmoregulation
6.4.9Controlling Blood Water Potential
6.4.10ADH
6.4.11End of Topic Test - Diabetes & Osmoregulation
6.4.12A-A* (AO3/4) - Homeostasis
7Genetics & Ecosystems (A2 only)
7.1Genetics
7.2Populations
7.3Evolution
7.3.1Variation
7.3.2Natural Selection & Evolution
7.3.3End of Topic Test - Populations & Evolution
7.3.4Types of Selection
7.3.5Types of Selection Summary
7.3.6Overview of Speciation
7.3.7Causes of Speciation
7.3.8Diversity
7.3.9End of Topic Test - Selection & Speciation
7.3.10A-A* (AO3/4) - Populations & Evolution
8The Control of Gene Expression (A2 only)
8.2Gene Expression
8.2.1Stem Cells
8.2.2Stem Cells in Disease
8.2.3End of Topic Test - Mutation & Gene Epression
8.2.4A-A* (AO3/4) - Mutation & Stem Cells
8.2.5Regulating Transcription
8.2.6Epigenetics
8.2.7Epigenetics & Disease
8.2.8Regulating Translation
8.2.9Experimental Data
8.2.10End of Topic Test - Transcription & Translation
8.2.11Tumours
8.2.12Correlations & Causes
8.2.13Prevention & Treatment
8.2.14End of Topic Test - Cancer
8.2.15A-A* (AO3/4) - Gene Expression & Cancer
8.3Genome Projects
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