4.3 Enzyme Inhibitors

Question 1

What are inhibitors?

Answer 1

Molecules that prevent enzymes from catalysing reactions

Question 2

Two types of inhibition

Answer 2

Competitive and non competitive

Question 3

Competitive inhibition

Answer 3

Molecule or part of a molecule that is a similar shape to the substrate of an enzyme can fit into the active site
This blocks substrate from entering active site, preventing catalysis - inhibition
Substrates and inhibitors will compete with each other to bind to the enzymes

Question 4

Effect of competitive inhibitor on rate of reaction

Answer 4

Reduces rate of reaction for certain concentration of substrate, but does not change V max of enzyme
If substrate concentration is increased, inhibition can be overcome

Question 5

Non competitive inhibition

Answer 5

Inhibitor binds to the enzyme at allosteric site
Binding of inhibitor causes tertiary structure of enzyme to change, so active site changes shape
Active site no longer has complementary shape to the substrate so is unable to bind to the enzyme

Question 6

Effect of non competitive inhibition on rate of reaction

Answer 6

Increasing enzyme/substrate concentration will not overcome the effect of non competitive inhibition
Increasing inhibitor concentration reduces rate of reaction further

Question 7

Examples of competitive inhibition

Answer 7

Statins are competitive inhibitors for enzymes that help synthesis of cholesterol
Aspirin irreversibly binds to active site of COX enzymes, prevents synthesis of prostaglandins and thromboxane (chemicals responsible for producing fever and pain)

Question 8

Examples of irreversible non competitive inhibitors

Answer 8

Organophosphates - used as insecticides and herbicides can inhibit an enzyme necessary for nerve impulse transmission - cause muscle cramps, paralysis
Proton pump inhibitors (PPIs) can be used to treat long term indigestion -block enzymes responsible for secreting hydrogen ions into stomach

Question 9

What is end product inhibition?

Answer 9

Enzyme inhibition where product of a reaction acts as an inhibitor to the enzyme that produces it - negative feedback control mechanism

Question 10

Metabolic pathway of respiration

Answer 10

Glucose is broken down
Add 2 phosphate groups to the glucose molecule
Addition of 2nd phosphate group is catalysed by PFK, competitively inhibited by ATP
When ATP levels are high, more ATP binds to allosteric site on PFK, preventing addition of 2nd phosphate group