3.1.3
Factors Affecting Enzyme Activity 2
Inhibition of Enzyme Activity
Inhibition of Enzyme Activity
Reaction rate is influenced by the presence of competitive and non-competitive inhibitors.


Function of 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
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
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
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.


Inactive precursors
Inactive precursors
- A zymogen is an inactive precursor to an enzyme.
- A zymogen needs to be cleaved to be activated, and the activation of the enzyme is irreversible.
- Inactive precursors are a way of regulating enzyme activity.
- An example of a zymogen is chymotrypsin, which is the precursor to trypsin, a digestive enzyme that works in the small intestine.
Coenzymes
Coenzymes
Some enzymes cannot catalyse a reaction without an additional molecule. These molecules include coenzymes, cofactors and prosthetic groups and they influence enzyme activity.


Cofactors
Cofactors
- Cofactors are small molecules that increase the activity of enzymes.
- When a cofactor binds to an enzyme, it undergoes a conformational change. The enzyme can now catalyse its reaction.
- Cofactors can be organic or inorganic molecules.
- E.g. Cl− is an inorganic cofactor to the enzyme amylase. When Cl− binds to amylase, it breaks down starch into sugars.


Coenzymes
Coenzymes
- Coenzymes are organic molecules that bind to enzymes to increase the speed of reaction.
- Coenzymes are a type of cofactor.
- E.g. Vitamins are an important source of coenzymes but they are not naturally produced in the body and must be supplied in the diet. If an individual's diet is low in vitamins, this can cause health problems because the enzymes cannot catalyse the necessary reactions.


Prosthetic groups
Prosthetic groups
- Prosthetic groups are inorganic molecules that permanently bind to enzymes to form part of the structure and increase the speed of reaction.
- Prosthetic groups are a type of cofactor.
- E.g. Zn2+ is a prosthetic group that forms part of carbonic anhydrase.
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
Jump to other topics
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
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