Question 1

Which of the following best describes the difference between a cofactor and a coenzyme?

Accepted Answer

A coenzyme is a loosely bound organic molecule that assists enzymes, while a cofactor can be either inorganic or organic and may be tightly or loosely bound.

Question 2

Which model of enzyme-substrate interaction is currently favored and why?

Accepted Answer

The induced fit model, because it accounts for conformational changes in the enzyme upon substrate binding.

Question 3

Given the Michaelis-Menten equation $$v = \frac{V_{max}[S]}{K_M + [S]}$$, what does a low $$K_M$$ value indicate about the enzyme?

Accepted Answer

The enzyme is saturated at low substrate concentrations.

Question 4

Which of the following best describes the effect of temperature on enzyme-catalyzed reaction rates?

Accepted Answer

Reaction rate increases with temperature up to a point, after which enzyme denaturation causes a decrease in rate.

Question 5

Which of the following statements about the transition state in enzyme-catalyzed reactions is correct?

Accepted Answer

Enzymes stabilize the transition state, lowering the activation energy ($$\Delta G$$^{\circ\ddagger}$$) required for the reaction.

Question 6

A patient is given an NSAID to relieve pain. Which enzyme is targeted, and what is the effect?

Accepted Answer

COX enzyme is inhibited, reducing prostaglandin synthesis and thus pain and inflammation.

Question 7

Which of the following best describes competitive inhibition?

Accepted Answer

The inhibitor binds to the active site, increasing $$K_M$$ but not affecting $$V_{max}.$$

Question 8

Which of the following is true regarding the Lineweaver-Burk plot for an enzyme with a competitive inhibitor?

Accepted Answer

The $$X-$$intercept moves closer to zero, indicating an increase in $$K_M.$$

Question 9

Which of the following is an example of an irreversible covalent modification?

Accepted Answer

Activation of a zymogen such as trypsinogen to trypsin.

Question 10

Which of the following best describes the role of E35 and D32 in the active site of lysozyme?

Accepted Answer

They are essential for catalysis, acting as acid and base to facilitate substrate cleavage.

Question 11

Which of the following is a ribozyme found in eukaryotic cells?

Accepted Answer

The ribosomal RNA (rRNA) component of the large ribosomal subunit.

Question 12

Which of the following best describes the steady-state assumption in Michaelis-Menten kinetics?

Accepted Answer

The concentration of enzyme-substrate complex remains constant during the initial phase of the reaction.

Question 13

If an enzyme has a turnover number ($$k_{cat}) of$$ $$1000\ 	ext{s}^{-1}$$ and a Michaelis constant ($$K_M) of$$ $$0.1\ 	ext{mM}$$, what is its catalytic efficiency?

Accepted Answer

$$k_{cat}/K_M = 10,000\ 	ext{mM}^{-1}	ext{s}^{-1}$$

Question 14

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

Accepted Answer

Increasing substrate concentration.

Question 15

Which of the following best describes feedback inhibition?

Accepted Answer

The end product of a pathway inhibits an earlier enzyme in the pathway.

Question 16

Which of the following statements about allosteric regulation is correct?

Accepted Answer

Allosteric effectors bind to a site other than the active site, causing conformational changes that affect enzyme activity.

Question 17

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

Accepted Answer

It decreases $$V_{max}$$ without affecting $$K_M.$$

Question 18

Which of the following is true about the half-life of a first-order reaction?

Accepted Answer

The half-life is independent of the initial concentration of reactant.

Question 19

A researcher observes that an enzyme's activity increases after phosphorylation. Which type of enzyme regulation is this?

Accepted Answer

Reversible covalent modification.

Enzymes: Biological Catalysts – Mechanisms, Kinetics, and Regulation

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