Question 1

Which of the following statements best describes how enzymes affect the activation energy of a reaction?

Accepted Answer

Enzymes decrease the activation energy, making reactions faster.

Question 2

Given the Arrhenius equation $$k = Ae$$^{\left(\frac{-\Delta G^{\circ \ddagger}$$}{RT}\right)}$$, what will happen to the rate constant $$k if $$the activation energy $$\Delta G$$^{\circ \ddagger}$$ is lowered by an enzyme?

Accepted Answer

The rate constant $$k$$ will increase.

Question 3

Which of the following is NOT a general mechanism by which enzymes catalyze reactions?

Accepted Answer

Increasing the standard free energy change ($$\Delta G$$^{\circ}$$)

Question 4

A mutation in chymotrypsin replaces Ser195 with alanine. What is the most likely effect on enzyme activity?

Accepted Answer

The enzyme will lose most of its catalytic activity.

Question 5

Which of the following best describes the role of the oxyanion hole in serine proteases?

Accepted Answer

It stabilizes the tetrahedral transition state intermediate.

Question 6

Which enzyme class does hexokinase belong to, and what reaction does it catalyze?

Accepted Answer

Transferase; phosphorylation of glucose

Question 7

In the Michaelis-Menten equation $$v = \frac{k_{cat}[E]_t[S]}{K_M + [S]}$$, what does $$K_M$$ represent?

Accepted Answer

The substrate concentration at which the reaction rate is half-maximal

Question 8

A Lineweaver-Burk plot of $$1/v$$ versus $$1/[S]$$ for an enzyme in the presence of a competitive inhibitor will show:

Accepted Answer

No change in the y-intercept and a less negative x-intercept

Question 9

Which of the following statements about $$k_{cat}/K_M is $$correct?

Accepted Answer

$$k_{cat}/K_M is a $$measure of enzyme specificity and catalytic efficiency.

Question 10

Which of the following best describes uncompetitive inhibition?

Accepted Answer

The inhibitor binds only to the enzyme-substrate complex.

Question 11

Which of the following is a real-world example of competitive enzyme inhibition?

Accepted Answer

Captopril inhibition of angiotensin-converting enzyme (ACE)

Question 12

Which statement about allosteric enzymes is FALSE?

Accepted Answer

They always follow Michaelis-Menten kinetics.

Question 13

Which of the following is a key advantage of regulating enzyme activity by phosphorylation?

Accepted Answer

It allows rapid and reversible changes in enzyme activity.

Question 14

Which of the following best explains why enzymes do not alter the equilibrium constant ($$K_{eq}) of a $$reaction?

Accepted Answer

Enzymes only affect the rate of reaction, not the overall free energy change ($$\Delta G$$^{\circ}$$).

Question 15

A patient is treated with a drug that acts as a noncompetitive inhibitor of an enzyme. Which of the following changes would you expect in the enzyme kinetics?

Accepted Answer

$$V_{max}$$ decreases, $$K_M$$ remains unchanged.

Question 16

Which of the following is true regarding the catalytic triad in chymotrypsin?

Accepted Answer

It consists of Ser195, His57, and Asp102, which work together to facilitate peptide bond hydrolysis.

Question 17

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

Accepted Answer

The enzyme changes conformation to better fit the substrate and stabilize the transition state.

Question 18

Which of the following statements about enzyme cofactors is correct?

Accepted Answer

Coenzymes are often derived from vitamins and are required for some enzyme activities.

Question 19

Which of the following is the correct unit for the rate constant of a second-order reaction?

Accepted Answer

$$\mathrm{M}^{-1}\mathrm{s}^{-1}$$

Chapter 8: Enzymes – Biological Catalysis and Kinetics

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