4.3 Enzyme Inhibitors

Question 1

What are enzyme inhibitors?

Answer 1

Molecules that prevent enzymes from carrying out their normal function of catalysis (or slow them down). There are two types of enzyme inhibition - competitive and non-competitive

Question 2

How does competitive inhibition work?

Answer 2

• a molecule or a part of a molecule that as a similar shape to the substrate of an enzyme can fit into the active site of the enzyme
• this blocks the substrate from entering the active, preventing the enzyme from catalysing the reaction
• the enzyme cannot carry out its function and is inhibited
• substrate and inhibitor molecules compete with each other to bind to the active sites of the enzymes. This will reduce the number of substrate molecules binding to active sites in a given time and slows down the reaction

Most competitive inhibitors only bind temporarily to the active site of the enzyme so their effect is reversible. However there are some exceptions such as aspirin

Question 3

What is a competitive inhibitor’s effect on rates of reaction?

Answer 3

A competitive inhibitor reduces the rate of reaction for a given concentration of substrate but it does not change the V max (maximum rate of reaction) of the enzyme

Question 4

How do non-competitive inhibitors work?

Answer 4

• the inhibitor binds to the enzyme at a location other than the active site. This alternative site is called an allosteric site
• the binding of the inhibitor causes the tertiary structure of the enzyme to change, meaning the active site changes shape
• this results in the active site no longer having a complementary shape to the substrate so it is unable to bind to the enzyme
• the enzyme cannot carry out its function and it is inhibited

Question 5

Effects on rate of reaction with non-competitive inhibition

Answer 5

Increasing the concentration of enzyme or substrate will not overcome the effect of a non-competitive inhibitor
Increasing the concentration of inhibitor, however, will decrease the rate of reaction further as more active sites become unavailable

Question 6

What is end-product inhibition?

Answer 6

Enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it
It is an example of non-competitive reservable inhibition