Question 1

Which of the following best describes the role of nicotinamide cofactors (NAD+/NADP+) in oxidoreductase-catalyzed reactions?

Accepted Answer

They transfer 2 electrons as a hydride ion.

Question 2

A patient is prescribed a statin drug to lower cholesterol. Statins are competitive inhibitors of HMG-CoA reductase. Which of the following best explains how statins lower cholesterol levels?

Accepted Answer

They compete with the natural substrate for the active site, reducing endogenous cholesterol synthesis.

Question 3

Which of the following statements about allosteric regulation of enzymes is CORRECT?

Accepted Answer

Binding of an allosteric effector to one site can change the affinity of the enzyme for its substrate at a different site.

Question 4

The conversion of glutamate to glutamine is thermodynamically unfavorable. Which strategy does the cell use to drive this reaction forward?

Accepted Answer

Coupling the reaction to ATP hydrolysis to form an acyl phosphate intermediate.

Question 5

Which of the following best describes the mechanism of penicillin as an antibiotic?

Accepted Answer

It is a reversible covalent inhibitor of bacterial transpeptidase, forming a stable ester linkage with a serine residue.

Question 6

A sigmoidal (S-shaped) curve in a plot of reaction rate versus substrate concentration is characteristic of which type of enzyme?

Accepted Answer

Allosteric enzyme with cooperative substrate binding

Question 7

Which of the following is a physiological consequence of inhibiting cGMP-specific phosphodiesterase 5 (PDE5)?

Accepted Answer

Increased cGMP levels and prolonged vasodilation

Question 8

Which of the following best explains why transition state analogs are effective enzyme inhibitors?

Accepted Answer

They bind to the enzyme's active site with higher affinity than the substrate by mimicking the transition state.

Question 9

Protein kinase A (PKA) is regulated by cAMP. Which of the following statements is TRUE regarding its regulation?

Accepted Answer

cAMP binds to the regulatory subunit, causing a conformational change that releases the catalytic subunit.

Question 10

Which of the following is an example of reversible covalent modification regulating enzyme activity?

Accepted Answer

Phosphorylation of serine, threonine, or tyrosine residues by protein kinases

Question 11

A patient is exposed to a nerve toxin that irreversibly inhibits acetylcholinesterase. What is the most likely physiological effect?

Accepted Answer

Continuous muscle contraction leading to paralysis and suffocation

Question 12

Which of the following best describes the effect of a competitive inhibitor on enzyme kinetics?

Accepted Answer

It does not change $$V_{max}$$ but increases $$K_M.$$

Question 13

Which of the following is TRUE regarding zymogens?

Accepted Answer

They require proteolytic cleavage to become active enzymes.

Question 14

Which of the following is a key feature of uncompetitive inhibition?

Accepted Answer

The inhibitor binds only to the enzyme-substrate complex, decreasing both $$V_{max}$$ and $$K_M.$$

Question 15

Which of the following best explains the mechanism of action of remdesivir as an antiviral drug?

Accepted Answer

It is incorporated into viral RNA by RNA-dependent RNA polymerase, causing premature chain termination.

Question 16

Which of the following statements about enzyme regulation is CORRECT?

Accepted Answer

Enzyme activity can be regulated by synthesis/degradation, sequestration, allosteric effectors, covalent modification, and inhibitors.

Question 17

Which of the following is a real-world example of an enzyme inhibitor used as a pharmaceutical drug?

Accepted Answer

Penicillin, which inhibits bacterial transpeptidase

Question 18

Which of the following statements about the regulation of glycogen phosphorylase is TRUE?

Accepted Answer

It is regulated by both covalent modification (phosphorylation/dephosphorylation) and allosteric effectors.

Question 19

Which of the following best describes the effect of CTP on the enzyme shown in the aspartate transcarbamoylase (ATCase) graph?

Accepted Answer

CTP acts as an allosteric inhibitor, shifting the curve to require higher [aspartate] for the same reaction rate.

Enzyme Mechanisms and Regulation – Biochemistry Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard