Question 1

Which of the following statements best explains why an enzyme increases the rate of a reaction but does not change the equilibrium constant or the overall free energy change ($$\Delta G) of $$the reaction?

Accepted Answer

Enzymes lower the activation energy ($$\Delta G$$^{\ddagger}$$) required to reach the transition state, but do not alter the free energy difference between substrate and product ($$\Delta G$$) or the equilibrium constant.

Question 2

Refer to the reaction coordinate diagram. What does the difference between $$\Delta G$$^{\ddagger}$$_{	ext{uncat}}$$ and $$\Delta G$$^{\ddagger}$$_{	ext{cat}}$$ represent?

Accepted Answer

The reduction in activation energy due to enzyme catalysis.

Question 3

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

Accepted Answer

The rate of formation of the enzyme-substrate complex (ES) equals the rate of its breakdown.

Question 4

Given the Michaelis-Menten equation $$V_0$$ = \frac{V_{\max}[S]}{K_m + [S]}$$, what is the initial velocity (V_0$) when $$[S] \gg K_m$$?

Accepted Answer

$$V_0 = V$$_{\max}$$

Question 5

Which of the following is true regarding $$K_m$$ and $$K_d$$ for an enzyme-catalyzed reaction?

Accepted Answer

$$K_m$$ approximates $$K_d$$ only when $$k_2$$ \ll k_{-1}$$.

Question 6

An enzyme has a $$V_{\max} of 100$$ $$\muM/$$min with 0.01 $$\muM $$total enzyme and a $$K_m of 5$$ $$\muM. $$What is the $$k_{cat}$$ value?

Accepted Answer

$$k_{cat} = 1,000$$ min$$^{-1}$$

Question 7

Which of the following Lineweaver-Burk plot patterns indicates a ping-pong (double displacement) mechanism for a two-substrate enzyme?

Accepted Answer

A series of parallel lines.

Question 8

Which type of reversible inhibitor increases the apparent $$K_m$$ but does not affect $$V_{\max}$$?

Accepted Answer

Competitive inhibitor

Question 9

If an enzyme-catalyzed reaction is measured only at a single endpoint after 2 hours, which of the following is NOT a valid reason why this is insufficient to characterize the enzyme?

Accepted Answer

The enzyme concentration is always equal to substrate concentration.

Question 10

Which of the following best describes the catalytic efficiency of an enzyme?

Accepted Answer

It is given by $$k_{cat}/K_m$$ and reflects both binding and catalytic turnover.

Question 11

Which of the following is a correct statement about the units of $$k_{cat}$$, $$K_m$$, and $$k_{cat}/K_m$$?

Accepted Answer

$$k_{cat}$$: s$$^{-1}$$, $$K_m$$: M, $$k_{cat}/K_m$$: M$$^{-1}s$^{-1}$$

Question 12

Which of the following best explains why enzymes that approach the diffusion limit are considered 'perfect' catalysts?

Accepted Answer

Their catalytic efficiency ($$k_{cat}/K_m) is $$limited only by how fast substrate can diffuse into the active site.

Question 13

Which of the following is a feature of uncompetitive inhibition?

Accepted Answer

Both $$V_{max}$$ and $$K_m$$ decrease by the same factor.

Question 14

A competitive inhibitor is added to an enzyme reaction. Which of the following changes would you expect in the Lineweaver-Burk plot?

Accepted Answer

The lines intersect on the y-axis, and the slope increases with inhibitor concentration.

Question 15

Which of the following best describes the role of the oxyanion hole in chymotrypsin catalysis?

Accepted Answer

It stabilizes the negative charge on the tetrahedral intermediate via hydrogen bonds.

Question 16

Which of the following is NOT a member of the chymotrypsin catalytic triad?

Accepted Answer

Lysine

Question 17

Which of the following best describes a zymogen?

Accepted Answer

An inactive enzyme precursor that requires proteolytic cleavage for activation.

Question 18

Which of the following statements about $$K$$ and $$k is $$correct?

Accepted Answer

$$K is an $$equilibrium constant and $$k is a $$rate constant.

Question 19

Which of the following best explains why a reaction with a large negative $$\Delta G^\circ ($$such as ATP hydrolysis) can still require an enzyme to proceed at a biologically relevant rate?

Accepted Answer

The reaction has a high activation energy ($$\Delta G$$^{\ddagger}$$) that makes it slow without a catalyst.

Comprehensive Study Notes: Enzyme Structure, Function, and Kinetics

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