Chapter 8.5.2 (Exam 2) Enzyme Inhibition

Question 1

What are the three types of reversible inhibition?

Answer 1

Competitive inhibitors

Noncompetitive inhibitors

Uncompetitive inhibitors

Question 2

What are competitive inhibitors?

Answer 2

Competes with natural substrate for binding sites

Degree of inhibition depends on concentrations of substrate and inhibitor

Question 3

What is one example of a competitive inhibitor? How does it function?

Answer 3

Competitive inhibitor – methotrexate (anti-cancer drug)

It binds to the enzyme that catalyzes formation of a coenzyme for purine formation (purines are needed for DNA replication and cell division)

Question 4

What are uncompetitive inhibitors?

Answer 4

Uncompetitive inhibitors bind to the enzyme-substrate complex, preventing release of products

Question 5

What are noncompetitive inhibitors (allosteric inhibitors)?

Answer 5

Noncompetitive inhibitors bind to enzyme at a different site (not the active site)

The enzyme changes shape and alters the active site (allostery)

Question 6

What is allosteric regulation?

Answer 6

a non-substrate molecule binds enzyme at a site different from the active site, which changes enzyme shape

Question 7

What are the two forms of allosteric regulation?

Answer 7

Active form—proper shape to bind substrate (activators)

Inactive form—cannot bind substrate (inhibitors)

Question 8

Does allostery lead to enzyme inhibition or activation?

Answer 8

Allosteric non-substrate molecule may be an inhibitor (inactive form) or an activator (active form)

Question 9

Describe the structure of allosteric enzymes.

Answer 9

Most allosteric enzymes are proteins with quaternary structure

The active site is on the catalytic subunit

Inhibitors and activators bind to other polypeptides called regulatory subunits, at regulatory sites (allosteric sites)

Question 10

Allosteric enzymes exhibit cooperativity, whereas non-allosteric enzymes do not. What does this say about the reaction rate with regard to the substrate concentration?

Answer 10

Cooperativity can cause the enzyme to change to a more optimal shape when binding to a substrate, increasing the rate of reaction

This leads to a more sigmoidal curve for allosteric enzymes, whereas the non-allosteric enzyme curve for reaction rate vs. substrate concentration is hyperbolic