Question 1

Which of the following best describes the role of enzymes in cellular reactions?

Accepted Answer

Enzymes lower the activation energy ($$E_A) $$required for a reaction to proceed.

Question 2

The hydrolysis of ATP in water is thermodynamically favorable ($$\Delta G = -7.3$$ kcal/mol), yet ATP remains stable for days. What explains this stability?

Accepted Answer

The activation energy ($$E_A) $$for hydrolysis is high, preventing rapid reaction.

Question 3

According to the Michaelis–Menten equation $$v_0$$ = \frac{V_{max}[S]}{K_m + [S]}$$, what does K_m$ represent?

Accepted Answer

The substrate concentration at which the reaction velocity is half of $$V_{max}.$$

Question 4

Which of the following statements about enzyme specificity is correct?

Accepted Answer

Enzyme specificity is determined by the shape and chemistry of the active site.

Question 5

A reaction catalyzed by an enzyme proceeds faster because:

Accepted Answer

The enzyme lowers the activation energy ($$E_A) by $$stabilizing the transition state.

Question 6

Which class of enzyme would catalyze the following reaction: $$A - PO_4$ + B \rightarrow A + B - PO_4$?

Accepted Answer

Transferases

Question 7

What is the effect of a competitive inhibitor on enzyme kinetics?

Accepted Answer

It increases $$K_m$$ but does not affect $$V_{max}.$$

Question 8

Which of the following best describes the induced-fit model of enzyme action?

Accepted Answer

The enzyme changes shape upon substrate binding, bringing necessary amino acid side chains into the active site.

Question 9

Which statement about enzyme regulation is correct?

Accepted Answer

Enzyme activity can be regulated by substrate-level regulation, allosteric regulation, and covalent modification.

Question 10

Feedback inhibition is best described as:

Accepted Answer

The final product of a pathway inhibits an earlier step in the pathway.

Question 11

Which of the following is true about ribozymes?

Accepted Answer

Ribozymes are RNA molecules with catalytic activity.

Question 12

A cell maintains a constant temperature (isothermal). Why is increasing temperature not a useful strategy for increasing reaction rates in cells?

Accepted Answer

Cells cannot increase temperature without risking denaturation of proteins.

Question 13

Which of the following is a property shared by all catalysts, including enzymes?

Accepted Answer

They increase reaction rates by lowering the activation energy ($$E_A).$$

Question 14

Which of the following best explains why enzymes are highly specific for their substrates?

Accepted Answer

The active site of the enzyme is a groove or pocket with high affinity for the intended substrate.

Question 15

Which of the following statements about enzyme inhibition is correct?

Accepted Answer

Irreversible inhibitors bind covalently and cause permanent loss of catalytic activity.

Question 16

Which of the following is an example of a cofactor required for enzyme activity?

Accepted Answer

A metal ion or a small organic molecule (coenzyme)

Question 17

If the substrate concentration $$[S] is $$much greater than $$K_m$$, what happens to the initial velocity $$v_0$$ according to the Michaelis–Menten equation?

Accepted Answer

It approaches the maximum velocity $$V_{max}.$$

Question 18

Which of the following best describes noncompetitive inhibition?

Accepted Answer

The inhibitor binds to a site other than the active site, reducing enzyme activity regardless of substrate concentration.

Question 19

Which of the following is a real-world example of enzyme regulation by covalent modification?

Accepted Answer

Addition or removal of phosphate groups to regulate enzyme activity.

Question 20

Which of the following statements about allosteric regulation is correct?

Accepted Answer

Allosteric enzymes have two conformations, one with affinity for substrate and one without.

Enzymes: The Catalysts of Life – Cell Biology Study Guide

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