Question

Questions #1-2 refer to Atorvastatin, which is a competitive inhibitor of the rate limiting step of cholesterol biosynthesis.

1. What is the downstream effect of treating cells with this competitive inhibitor?

A. Atorvastatin decreases the Vmax of HMG CoA synthase.

B. Atorvastatin decreases the KM of HMG CoA synthase.

C. Atorvastatin decreases the Vmax of HMG CoA reductase.

D. Atorvastatin decreases the KM of HMG CoA reductase.

E. Atorvastatin increases the KM of HMG CoA reductase.

2. Mechanistically, how does Atorvastatin decrease cholesterol synthesis?

A. It binds to the enzyme-substrate complex and prevents the enzyme from catalyzing the reaction.

B. It occupies the active site of the enzyme, requiring higher concentrations of substrate to fully stimulate the enzyme.

C. It binds to the substrate, preventing the enzyme’s active site from recognizing the substrate.

D. It binds and sequesters substrate so that it isn’t available for the enzyme to bind.

E. It increases the degradation of the enzyme.

Answer 1

1. Statins are HMGR (HMG-CoA reductase) inhibitors, thus, reducing cholesterol synthesis. They act by reducing the Vmax of HMG CoA reductase.

Answer: C

2. Averostatins increases the rate of degradation of HMG CoA reductase. The half-life of the enzyme is found to decrease.

Answer: E