Question 1

Which statement best describes how a catalyst affects a chemical reaction?

Accepted Answer

A catalyst accelerates the approach to equilibrium by lowering the activation energy, but is not changed in the overall process.

Question 2

Which major class of enzyme catalyzes the transfer of a phosphate group from ATP to glucose?

Accepted Answer

Transferase

Question 3

According to the induced fit model of enzyme-substrate interaction, what happens when glucose binds to hexokinase?

Accepted Answer

The enzyme undergoes a conformational change to better accommodate the substrate.

Question 4

Which of the following is NOT a mechanism by which enzymes achieve rate acceleration?

Accepted Answer

Increasing the activation energy of the transition state

Question 5

A patient is diagnosed with a deficiency in thiamine (vitamin B$$_1). $$Which coenzyme and reaction type would most likely be affected?

Accepted Answer

Thiamine pyrophosphate; activation and transfer of aldehydes

Question 6

Which metal ion is essential for the catalytic activity of alcohol dehydrogenase and helps bind NAD$$^+$$?

Accepted Answer

Zn

Question 7

A drug acts as a competitive inhibitor of an enzyme. Which of the following is true regarding its mechanism?

Accepted Answer

It competes with the substrate for binding at the enzyme's active site.

Question 8

Which type of reversible enzyme inhibition involves the inhibitor binding only to the enzyme-substrate (ES) complex?

Accepted Answer

Uncompetitive inhibition

Question 9

Diisopropyl fluorophosphate (DFP) causes paralysis by which mechanism?

Accepted Answer

Covalent modification of the active site serine in acetylcholinesterase

Question 10

Which regulatory mechanism is most efficient for maintaining homeostasis in a metabolic pathway?

Accepted Answer

Feedback inhibition at committed steps

Question 11

Allosteric enzymes typically exhibit which of the following properties?

Accepted Answer

They are multisubunit proteins that change conformation upon binding substrates or effectors.

Question 12

Which statement about phosphorylation and dephosphorylation is correct?

Accepted Answer

Phosphorylation is reversible and carried out by protein kinases; dephosphorylation is performed by protein phosphatases.

Question 13

Which of the following best describes feedback inhibition in a metabolic pathway?

Accepted Answer

The end product of a pathway inhibits the first enzyme in the pathway.

Question 14

A mutation causes an enzyme to lose its ability to undergo conformational change upon substrate binding. Which model of substrate binding is most affected?

Accepted Answer

Induced fit model

Question 15

Which of the following statements about ribozymes is TRUE?

Accepted Answer

Ribozymes are RNA molecules that catalyze chemical reactions.

Question 16

Which of the following equations represents the total enzyme concentration in the presence of a competitive inhibitor?

Accepted Answer

$$[E]_T = [E] + [ES] + [EI]$$

Question 17

Which of the following is an example of irreversible covalent modification that activates an enzyme?

Accepted Answer

Proteolytic cleavage of zymogens

Question 18

A researcher discovers a new enzyme that is activated by the binding of a non-substrate molecule. What type of regulation is this?

Accepted Answer

Heteroallostery

Question 19

Which of the following statements about enzyme inhibition is correct?

Accepted Answer

Reversible inhibitors are noncovalently bound to the enzyme.

Question 20

Which of the following mechanisms is LEAST likely to be used for fine-tuned regulation of enzyme activity in a cell?

Accepted Answer

Substrate level control

Enzymes: Biological Catalysts – Principles, Mechanisms, and Regulation

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