Question 1

Which of the following best describes how enzymes affect the activation energy ($$E_A) $$and free energy change ($$\Delta G) of a $$chemical reaction?

Accepted Answer

Enzymes lower $$E_A$$ but do not affect $$\Delta G.$$

Question 2

A patient is prescribed allopurinol to treat gout. Which enzyme is being inhibited, and what type of inhibition is this?

Accepted Answer

Xanthine oxidase; competitive inhibition

Question 3

Which of the following statements about the induced-fit model of enzyme action is correct?

Accepted Answer

Substrate binding induces a conformational change in the enzyme, optimizing catalysis.

Question 4

Which of the following amino acids is LEAST likely to be found in the active site of an enzyme?

Accepted Answer

Valine

Question 5

A researcher increases the substrate concentration in an enzyme-catalyzed reaction, but the reaction rate no longer increases. What is the most likely explanation?

Accepted Answer

The enzyme is saturated; all active sites are occupied.

Question 6

Which of the following best describes the Michaelis-Menten constant ($$K_m$$)?

Accepted Answer

$$K_m is $$the substrate concentration at which the reaction velocity is half-maximal.

Question 7

Which of the following is NOT a property shared by all catalysts, including enzymes?

Accepted Answer

They are consumed in the reaction.

Question 8

Which of the following is an example of a ribozyme?

Accepted Answer

Peptidyl transferase in the ribosome

Question 9

A mutation causes an enzyme to lose its ability to bind its coenzyme. What is the most likely consequence?

Accepted Answer

The enzyme will lose catalytic activity.

Question 10

Which of the following best explains why enzymes are sensitive to pH?

Accepted Answer

pH changes can alter the charge of amino acids at the active site, disrupting ionic and hydrogen bonds.

Question 11

Which of the following scenarios describes noncompetitive inhibition?

Accepted Answer

An inhibitor binds to a site other than the active site, causing a conformational change that reduces enzyme activity.

Question 12

Which of the following regulatory mechanisms involves the end product of a pathway inhibiting an earlier step by binding to a site distinct from the active site?

Accepted Answer

Feedback inhibition (allosteric regulation)

Question 13

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 14

Which of the following is an example of covalent modification regulating enzyme activity?

Accepted Answer

Phosphorylation of serine residues by protein kinases

Question 15

A patient has a genetic mutation that causes the enzyme hexokinase to have a much lower $$K_m$$ for glucose. What is the most likely effect?

Accepted Answer

Hexokinase will be effective at lower glucose concentrations.

Question 16

Which of the following best describes the role of proteolytic cleavage in enzyme regulation?

Accepted Answer

It irreversibly activates zymogens by removing part of the polypeptide chain.

Question 17

Which of the following is true regarding the effect of temperature on enzyme activity?

Accepted Answer

Enzyme activity increases with temperature up to an optimal point, then decreases due to denaturation.

Question 18

Which of the following is a correct statement about the RNA World Hypothesis?

Accepted Answer

Early life forms used RNA for both genetic information storage and catalysis.

Question 19

Which of the following best describes the turnover number ($$k_{cat}) of an $$enzyme?

Accepted Answer

$$k_{cat} is $$the number of substrate molecules converted to product per enzyme molecule per unit time at V_{max}.

Question 20

Which of the following is NOT a way that enzymes can activate substrates?

Accepted Answer

Permanent covalent modification of the enzyme

Enzymes: The Catalysts of Life – Structure, Function, and Regulation

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