Factors Affecting Enzyme Activity

Investigating Rates of Enzyme-Controlled Reactions

Changes to the tertiary structure of an enzyme through changing the pH or temperature will affect how fast reactions are catalysed.

Temperature

Increasing the temperature will increase the kinetic energy of the molecules.
This increases the chance of a collision between the enzyme and substrate and so more collisions are likely in a set period of time. In other words, the rate of reaction is faster.
Increasing the temperature by 10^oC will approximately double the rate of reaction for most enzyme-controlled reactions.

Illustrative background for pH ?? "content

pH

Changing the pH changes the number of hydroxide ions and hydrogen ions (OH⁻ and H⁺) surrounding the enzyme.
These interact with the charges on the enzyme’s amino acids, affecting hydrogen bonding and ionic bonding, so resulting in changes to the tertiary structure.

Denatured enzymes

Increasing or decreasing the temperature or pH outside of an optimal range can affect chemical bonds within the active site and the enzyme will not work as well.
- At extreme temperatures and pH values, the enzyme's structure may be changed. This is called a denatured enzyme.

Enzyme and Substrate Concentration

Reaction rate is influenced by the relative enzyme and substrate concentrations.

Enzyme concentration

Increasing the concentration of enzyme in a solution means there are more enzyme molecules available to catalyse the substrate in a given amount of time

Substrate concentration

Increasing the concentration of the substrate increases the numbers of substrate molecules that can form enzyme-substrate (ES) complexes at any one time.
This increases the initial rate of reaction but when all the enzyme molecules are engaged in ES complexes the rate cannot increase any further.
The rate will then plateau because the enzyme is said to be saturated.

Inhibition of Enzyme Activity

Reaction rate is influenced by the presence of competitive and non-competitive inhibitors.

Function of competitive inhibitors

Inhibitors are chemicals that slow down the rate or stop the reaction altogether.
Enzyme-substrate complexes cannot be formed or are formed at a much lower rate.

Structure of competitive inhibitors

Competitive inhibitors are similar in shape to the usual substrate and affect the active site directly, blocking access for the formation of ES complexes.
Increasing the substrate concentration can compensate for the effects of a competitive inhibitor as there is no permanent damage to the shape of the active site.
- Malonate ions are similar in shape to succinate ions and act as a competitive inhibitor of succinate dehydrogenase, an important enzyme in the Krebs cycle.

Function of non-competitive inhibitors

Some non-competitive inhibitors have reversible effect but others are irreversible and denature the enzyme.
- E.g. Lead denatures a number of enzymes required to synthesise haemoglobin.

Structure of non-competitive inhibitors

Non-competitive inhibitors affect another part of the enzyme molecule causing a change to the shape of the active site.
The active site is no longer complementary to the substrate molecules.

1Cell Biology

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

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

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4.4Climate Change

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4.4.3Global Warming

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5Evolution & Biodiversity

5.1Evidence for Evolution

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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

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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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