2.4.1

Enzymes

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Enzymes

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

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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

  • 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

  • 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

  • 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.

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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 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:

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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

  • 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.

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1Cell Biology

1.1Introduction to Cells

1.1.1Introduction to Cells

1.1.2Cell Size & Surface Area

1.1.3Surface Area to Volume Ratio

1.1.4Eukaryotic vs Prokaryotic Cells

1.1.5Stem Cells

1.1.6Stem Cells in Disease

1.2Ultrastructure of Cells

1.2.1Eukaryotic Cells & Organelles

1.2.2Golgi, Lysosomes & Ribosomes

1.2.3Cell Walls & Vacuole

1.2.4Prokaryotes

1.2.5Binary Fission

1.2.6Subcellular Components & Organelles

1.3Membrane Structure

1.3.1Cell Membrane Structure & Permeability

1.4Membrane Transport

1.4.1Passive Movement Across Membranes

1.4.2Active Movement Across Membranes

1.4.3Endocytosis & Exocystosis

1.5The Origin of Cells

1.5.1Origins - Endosymbiosis

1.6Cell Division

1.6.1The Cell Cycle

1.6.2Mitosis

1.6.3Regulation of the Cell Cycle

1.6.4End of Topic Quiz - The Cell Cycle

1.6.5IB Multiple Choice - The Cell Cycle

1.6.6Extended Response - Mitosis

2Molecular Biology

2.1Water

2.1.1Water & Hydrogen Bonding

2.1.2IB Multiple Choice - Water & Hydrogen Bonding

2.1.3Extended Response - Water

2.2Carbohydrates & Lipids

2.2.1Monosaccharides

2.2.2Disaccharides & Polysaccharides

2.2.3Triglycerides & Phospholipids

2.2.4Cellulose

2.2.5Starch & Glycogen

2.3Proteins

2.3.1Structure & Functions of Proteins

2.4Enzymes

2.4.1Enzymes

2.4.2Factors Affecting Enzyme Activity

2.4.3Enzyme-Controlled Reactions

2.4.4End of Topic Test - Enzymes

2.5Structure of DNA & RNA

2.5.1DNA & RNA

2.6DNA Replication, Transcription & Translation

2.6.1Protein Synthesis

2.6.2Transcription & Translation

2.6.3End of Topic Test - DNA, Genes & Protein Synthesis

2.6.4Exam-Style Question - Protein Synthesis

2.6.5End of Topic Test - Coronavirus Translation

2.6.6IB Multiple Choice - Transcription

2.6.7IB Multiple Choice - Translation

2.7Cell Respiration

2.7.1Overview of Respiration

2.7.2Anaerobic Respiration

2.7.3End of Topic Test - Anaerobic Respiration

2.7.4Respiration Experiments

2.7.5End of Topic Test - Respiration

2.7.6IB Multiple Choice - Respiration

2.8Photosynthesis

2.8.1Overview of Photosynthesis

3Genetics

3.1Genes

3.1.1Genes

3.1.2Mutations

3.2Chromosomes

3.2.1Chromosomal Theory of Inheritance

3.2.2Chromosomal Basis of Inherited Disorders

3.2.3IB Multiple Choice - Chromosomal Inheritance

3.3Meiosis

3.3.1Meiosis

3.3.2Mitosis vs Meiosis

3.3.3Meiosis & Genetic Diversity

3.3.4End of Topic Quiz - Meiosis

3.3.5IB Multiple Choice - Meiosis

3.4Inheritance

3.4.1Key Terms

3.4.2Mendelian Genetics & Common Ancestry

3.4.3Mendelian Laws

3.4.4Monohybrid Crosses & Law of Segregation

3.4.5Introduction to Non-Mendelian Inheritance

3.4.6Codominance

3.4.7Multiple Alleles

3.5Genetic Modification & Biotechnology

3.5.1DNA Technology

3.5.2PCR & Gel Electrophoresis

3.5.3Genetic Modification

3.5.4Cloning

4Ecology

4.1Species, Communities & Ecosytems

4.1.1Population Dynamics

4.1.2Communities & Measuring Diversity

4.1.3Relationships Between Populations

4.1.4Overview of Ecosystems

4.1.5Nutrient Cycles

4.1.6Fertilisers

4.1.7Eutrophication

4.1.8Chi-Squared Test

4.2Energy Flow

4.2.1Energy

4.2.2Energy Flow

4.2.3Biomass & Food Chains

4.2.4Heterotrophs & Autotrophs

4.3Carbon Cycle

4.3.1Carbon Cycle

4.4Climate Change

4.4.1Carbon Dioxide

4.4.2The Greenhouse Effect

4.4.3Global Warming

4.4.4Maintaining Biodiversity

5Evolution & Biodiversity

5.1Evidence for Evolution

5.1.1Evidence for Evolution - Fossils & DNA

5.1.2Evidence for Evolution - Anatomy & Geography

5.1.3IB Multiple Choice - Evidence for Evolution

5.1.4Extended Response - DNA & Evolution

5.2Natural Selection

5.2.1Introduction

5.2.2Evolutionary Fitness

5.2.3Natural Selection & Variation

5.2.4End of Topic Quiz - Natural Selection

5.2.5IB Multiple Choice - Natural Selection

5.2.6Speciation

5.3Classification of Biodiversity

5.3.1Introduction to Biodiversity

5.3.2Keystone Species

5.3.3Courtship & Ancestry

5.3.4Classification

5.4Cladistics

5.4.1Evolutionary Relationships

5.4.2IB Multiple Choice - Species & Taxonomy

6Human Physiology

6.1Digestion & Absorption

6.1.1Overview of Digestion

6.1.2Digestion in Mammals

6.1.3Absorption

6.1.4End of Topic Test - Substance Exchange & Digestion

6.1.5End of Topic Test - Substance Ex & Digestion

6.2The Blood System

6.2.1The Circulatory System

6.2.2The Heart

6.2.3Blood Vessels

6.2.4Cardiovascular Disease

6.3Defence Against Infectious Disease

6.3.1Immune System

6.3.2The Immune Response

6.3.3Antibodies

6.3.4Primary & Secondary Response

6.3.5Vaccines

6.3.6HIV

6.3.7End of Topic Test - Immune System

6.3.8Exam-Style Question - Immune System

6.3.9End of Topic Test - Immune System

6.4Gas Exchange

6.4.1Lung Structure & Alveoli

6.4.2Ventilation

6.4.3Lung Disease

6.4.4Lung Disease Data

6.5Neurons & Synapses

6.5.1Neuron Structure

6.5.2Transmission of an Impulse

6.5.3Speed of Transmission

6.5.4End of Topic Test - Neurones & Action Potentials

6.5.5Synapses

6.5.6Types of Synapse

6.5.7Medical Application

6.5.8End of Topic Test - Synapses

6.5.9End of Topic Test - Nervous Comm&Coord

6.6Hormones, HomeoStasis & Reproduction

6.6.1Overview of Homeostasis

6.6.2Blood Glucose Concentration

6.6.3Controlling Blood Glucose Concentration

6.6.4End of Topic Test - Blood Glucose

6.6.5Type I & Type II Diabetes

6.6.6Human Reproductive Systems

6.6.7Hormonal Control of the Menstrual Cycle

7AHL: Nucleic Acids

7.1DNA Structure & Replication

7.1.1DNA

7.1.2RNA

7.1.3DNA Replication

7.1.4DNA Replication - Summary

7.1.5IB Multiple Choice - DNA Replication

7.2Transcription & Gene Expression

7.2.1Introduction to Transcription & Protein Synthesis

7.2.2Types of RNA

7.2.3Transcription

7.2.4RNA Processing in Eukaryotes

7.2.5IB Multiple Choice - Transcription

7.3Translation

7.3.1Translation

7.3.2Retroviruses

7.3.3Scientific Practices: Coronavirus

7.3.4IB Multiple Choice - Translation

8AHL: Metabolism, Cell Respiration & Photosynthesis

8.1Metabolism

8.1.1Molecules to Metabolism

8.2Cell Respiration

8.2.1Glycolysis

8.2.2Aerobic Respiration

8.3Photosynthesis

8.3.1Light-Dependent Reaction

8.3.2Light-Independent Reaction

8.3.3End of Topic Test - Photosynthesis Reactions

8.3.4Limiting Factors

8.3.5Photosynthesis Experiments

8.3.6End of Topic Test - Photosynthesis

8.3.7End of Topic Test - Photosynthesis

9AHL: Plant Biology

9.1Transport in the Xylem of Plants

9.1.1Structure

9.1.2Cohesion-Tension Theory

9.1.3Investigating Transpiration Rate

9.2Transport in the Phloem of Plants

9.2.1Structure

9.2.2Translocation

9.3Growth in Plants

9.3.1Plant Tropisms

10AHL: Genetics & Evolution

10.1Meiosis

10.1.1Stages of Meiosis

10.2Inheritance

10.2.1Linked Genes

10.2.2Sex-Linked Genes

10.2.3Non-Nuclear Inheritance

10.2.4Chi-Squared Test

10.2.5End of Topic Quiz - Inheritance

10.2.6IB Multiple Choice - Non-Mendelian Genetics

10.2.7Introduction to Non-Mendelian Inheritance

10.2.8Extended Response - Inheritance

10.2.9Grade 4-5 (Scientific Practices) - Inheritance

10.3Gene Pools & Speciation

10.3.1Populations

10.3.2Mutations, Genetic Drift, & Gene Flow

10.3.3Speciation

10.3.4Rate of Speciation

10.3.5Allopatric & Sympatric Speciation

11AHL: Animal Physiology

11.1Antibody Production & Vaccination

11.1.1Immune System

11.1.2The Immune Response

11.1.3Antibodies

11.1.4Primary & Secondary Response

11.1.5Vaccines

11.2Movement

11.2.1Skeletal Muscle

11.2.2Sliding Filament Theory

11.2.3Contraction

11.3The Kidney & Osmoregulation

11.3.1Kidneys & Osmoregulation

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Structure & Functions of Proteins

Factors Affecting Enzyme Activity