Question 1

Which of the following best describes the role of an enzyme's active site in catalysis?

Accepted Answer

It provides a region where substrates are brought together and stabilized in the transition state, lowering the activation energy.

Question 2

Which equation represents the Michaelis-Menten relationship for initial velocity ($$v_0) as a $$function of substrate concentration ($$[S]$$)?

Accepted Answer

$$v_0$$ = \dfrac{V_{max}[S]}{K_m + [S]}$$

Question 3

A competitive inhibitor affects enzyme kinetics by:

Accepted Answer

Increasing $$K_m$$ and leaving $$V_{max}$$ unchanged.

Question 4

Which enzyme class catalyzes the transfer of functional groups between molecules?

Accepted Answer

Transferases

Question 5

An enzyme that requires a tightly bound organic cofactor derived from a vitamin is said to have a:

Accepted Answer

Prosthetic group

Question 6

Which of the following statements about allosteric enzymes is TRUE?

Accepted Answer

They typically display sigmoidal $$v vs$$. $$[S]$$ curves due to cooperative substrate binding.

Question 7

In a Lineweaver-Burk plot, which of the following changes would you expect in the presence of a noncompetitive inhibitor?

Accepted Answer

The $$y-$$intercept increases, but the $$x-$$intercept remains unchanged.

Question 8

Which of the following is the correct definition of the turnover number ($$k_{cat}) $$for an enzyme?

Accepted Answer

The number of substrate molecules converted to product per enzyme molecule per unit time when the enzyme is saturated with substrate.

Question 9

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

Accepted Answer

The active site has a unique three-dimensional structure that only fits specific substrates.

Question 10

A patient is given a drug that acts as an uncompetitive inhibitor for an enzyme involved in glucose metabolism. What effect will this have on the enzyme's $$K_m$$ and $$V_{max}$$?

Accepted Answer

Both $$K_m$$ and $$V_{max}$$ will decrease.

Question 11

Which of the following is a real-world example of feedback inhibition in metabolic pathways?

Accepted Answer

ATP inhibits phosphofructokinase in glycolysis.

Question 12

Which equation describes the effect of temperature on the rate constant $$k$$ for a chemical reaction?

Accepted Answer

$$k = A \exp\left(-\dfrac{E_a}{RT}\right)$$

Question 13

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

Accepted Answer

Enzymes lower the activation energy ($$\Delta G$$^{\ddagger}$$) for the reaction.

Question 14

Which of the following is the best measure of catalytic efficiency for an enzyme under physiological (non-saturating) substrate concentrations?

Accepted Answer

$$k_{cat}/K_m$$

Question 15

A mutation in an allosteric enzyme causes it to favor the T (tense) state over the R (relaxed) state. What is the most likely effect on the enzyme's activity?

Accepted Answer

The enzyme will become less active and show decreased substrate binding.

Question 16

Which of the following is a characteristic of irreversible enzyme inhibitors?

Accepted Answer

They bind covalently to the active site and permanently inactivate the enzyme.

Question 17

Which of the following best describes the concerted model of allosteric regulation?

Accepted Answer

All subunits of the enzyme switch between T and R states simultaneously.

Question 18

Which of the following is true about the role of cofactors in enzyme activity?

Accepted Answer

Holoenzymes are active forms of enzymes with their cofactors bound.

Question 19

Which of the following scenarios would most likely result in a diffusion-controlled reaction for an enzyme?

Accepted Answer

The catalytic efficiency ($$k_{cat}/K_m) $$approaches $$10^8 to$$ $$10^9 M$^{-1}s$^{-1}.$$

Enzyme Properties, Classification, and Kinetics: A Study Guide

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