Enzyme inhibition

Question 1

What are enzyme inhibitors?

Answer 1

Substances that directly/indirectly interfere with functioning of active site + reduces enzyme activity

Question 2

What are the two types of inhibitors and what do they do?

Answer 2

• Competitive: bind to the active site of the enzyme

* Non-competitive: bind to the enzyme at a position other than the active site

Question 3

Describe what happens during competitive inhibition

Answer 3

• Competitive inhibitors have a molecular shape similar to the substrate
• It allows them to occupy active site of enzyme + compete with substrate for available active sites
• Effect on enzyme activity is dependent on conc. of inhibitor + substrate - if substrate conc. is increased, effect of inhibitor reduced
• Inhibitor is not permanently bound to active site so substrate/inhibitor can take its place
• The greater the conc. of inhibitor the longer it will take for substrates to occupy active sites (sooner or later all the substrates will occupy the active sites)

Question 4

Give an example of competitive inhibition

Answer 4

• An important respiratory enzyme acts on succinate but malonate can inhibit the respiratory enzyme
• Malonate has a very similar shape to succinate + blocks succinate from combining with the enzyme’s active site

(Another example is that enzyme transpeptidase which can be inhibited by penicillin)

Question 5

Describe non-competitive inhibition

Answer 5

• Non-competitive inhibitors attach themselves to enzyme at a binding site which is NOT the active site
• Upon attaching to enzyme, the inhibitor alters the shape of the enzyme + its active site, therefore the substrate can’t bind to it. So, the enzyme can not function
• As substrate + inhibitor are not competing for same site, an increase in substrate conc. does not decrease the effect of the inhibitor