Mini 1 Enzymology 2 PQ

Which one of the following statements regarding enzyme inhibition is correct? A. Competitive inhibition is seen when a substrate competes with an enzyme for binding to an inhibitor protein. B. Competitive inhibition is seen when the substrate and the inhibitor compete for the active site on the enzyme. C. Non-competitive inhibition of an enzyme can be overcome by adding large amount of substrate D. Non-competitive inhibitors often bind to the enzyme irreversibly.

B

Allosteric ligands can modify enzymatic activity when they bind. Which of the following kinetic parameters can potentially be modified by such binding? A. Km B. Vmax C. Km and Vmax D. KI

C

The substrate concentration dependencies of two different enzymes are best compared using which characteristic enzyme parameter? A. Rate of Product formation B. Optimum pH value C. KM value D. Molecular weight of the enzyme

C

ADP and and glucose 6-phosphate both act as allosteric regulators of hexokinase. Both are products of the enzymatic reaction. While the inhibition of hexokinase by glucose 6-phosphate can be considered product inhibition, the action of ADP is to activate hexokinase. Which of the following explanations is most parsimonious with these observations? A) ADP and glucose 6-phosphate counteract each other's effects. B) Glucose 6-phosphate inhibits as a sensor of its accumulation, while ADP is a sensor for the energy state of the cell. C) The affinity of ADP is too low to have any substantial effect on the enzyme; only glucose 6-phosphate is important. D) Both sites are vestigial sites derived from copies of the active site and do not affect biological function.

B

When discussing alcohol dehydrogenase, what is the relationship between methanol and ethanol? A. Ethanol is a substrate and methanol is an allosteric inhibitor B. Ethanol and methanol are competitive with each other C. Ethanol and methanol are co-substrates D. Both compounds allosterically affect enzyme activity E. Both are substrates but neither compound affects the activity on the other

B

A form of hexokinase has a Km of about 500 micromolar for glucose. If the intracellular glucose concentration is 5 mM, what will the approximate velocity of this isozyme be relative to the Vmax? A. ¼ Vmax B. ½ Vmax C. ¾ Vmax D. 9/10 Vmax E. Vmax

D

You measure the enzyme kinetics of a novel enzyme and you find the velocity at 3 mM to be 25% of the Vmax. What is the Km of this enzyme? A. 0.75 mM B. 3 mM C. 6 mM D. 9 mM E. 12 mM F. 20 mM

D

Many drugs function as inhibitors for enzyme reactions. If the Vmax of an enzyme is 15 units/min/mg protein, with a Km of 1.25 µM in the absence of inhibitor, and a Vmax of 6 units/min/mg protein with a Km unchanged in the presence of inhibitor, what will the enzyme velocity be in the presence of inhibitor at a substrate concentration of 2.5 µM? A. 1 unit/min/mg protein B. 2 units/min/mg protein C. 1.25 units/min/mg protein D. 2.5 units/min/mg protein E. 4 units/min/mg protein F. 5 units/min/mg protein G. 6 units/min/mg protein

E

Statins compete with what compound on the enzyme HMG-CoA reductase? A. Cholesterol B. Acetyl-CoA C. Coenzyme A D. Malonyl-CoA E. HMG-CoA

E

What are the initial rate conditions for measuring enzyme activity?

changes in substrate and product concentration are both small; early time

Name an instance of noncompetitive inhibition that is clinically important

antibiotics

Non-competitive binding occurs where on an enzyme?

binds to a regulatory site

Statins act by what mechanism?

competitive inhibition

A sigmoid curve of velocity versus concentration is indicative of what?

cooperative binding

What parameters are changed with uncompetitive inhibition?

decreased km and Vmax

What is a Lineweaver-Burk transformation?

double reciprocal plot of Michaelis-Menten curve

What is the advantage of a semilog plot for comparing kinetic data?

easier to read exponential relationship

The units of Km and Vmax are what?

moles/L

Name two examples of suicide inhibitors.

ASA, nerve gases, proton pump inhibitors, penicillin

Statins act on what enzyme?

HMG CoA

What 2 parameters are obtained from a Michaelis-Menten curve?

Km and Vmax

Non-competitive inhibition shows changes in what Michaelis-Menten parameter?

Vmax decreases

Suicide inhibition shows what change in the Michaelis-Menten parameters?

Vmax decreases

Where do competitive inhibitors bind?

active site

Suicide inhibition occurs where on the enzyme?

active site?

Competitive binding shows changes in what Michaelis-Menten parameter?

increased Km