Lecture 12 - control of enzyme activity

Question 1

what is an inhibitor

Answer 1

a compound that binds to an enzyme and reduces its activity

Question 2

what is irreversible inhibition

Answer 2

• binds covalently
• permanently inactivates that enzyme

Question 3

what is reversible inhibition

Answer 3

• not covalently bound
• binds to the enzyme but then can subsequently be released

Question 4

what is competitive inhibition

Answer 4

• inhibitor competes directly with the substrate for the active site
• either inhibitor or substrate will bind to the enzyme

Question 5

what happens to Vmax and Km in competitive inhibition

Answer 5

• Vmax stays the same
• Km increases

Question 6

what is pure non competitive inhibition

Answer 6

• inhibitor binds at a different site than the substrate
• enzyme can bind to substrate or inhibitor or both at the same time

Question 7

what happens to Vmax and Km in pure inhibition

Answer 7

• Vmax decreases
• Km stays the same

Question 8

what happens in mixed inhibition

Answer 8

changes in both Vmax and Km

Question 9

what are the methods of enzyme regulation (5)

Answer 9

• covalent modification (e.g phosphorylation)
• allosteric effects = binding at points not active site
• proteolytic cleavage (e.g gut proteases, made in inactive form and then activated
• turn gene expression on or off
• degrade the enzyme