Question 1

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

Accepted Answer

Enzymes lower the activation energy ($$E_A) $$required for a reaction, increasing the reaction rate.

Question 2

A reaction in a cell is thermodynamically favorable but does not occur at a significant rate. What is the most likely explanation?

Accepted Answer

The reaction has a high activation energy ($$E_A) $$barrier.

Question 3

Which of the following statements about enzyme active sites is CORRECT?

Accepted Answer

Active sites are three-dimensional pockets formed by protein folding, where substrates bind with high specificity.

Question 4

Which of the following is an example of a cofactor that is a small organic molecule derived from vitamins?

Accepted Answer

Coenzyme A

Question 5

Which enzyme class is responsible for catalyzing the transfer of functional groups from one molecule to another?

Accepted Answer

Transferases

Question 6

A patient is exposed to nerve gas, which irreversibly inhibits acetylcholinesterase. What is the molecular basis for this inhibition?

Accepted Answer

The inhibitor binds covalently to the enzyme, causing permanent loss of activity.

Question 7

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

Accepted Answer

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

Question 8

Which of the following is TRUE regarding the Michaelis–Menten constant ($$K_m$$)?

Accepted Answer

$$K_m is a $$measure of the enzyme's affinity for its substrate; a low $$K_m$$ indicates high affinity.

Question 9

A competitive inhibitor affects enzyme kinetics in which of the following ways?

Accepted Answer

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

Question 10

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

Accepted Answer

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

Question 11

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

Accepted Answer

Phosphorylation of a serine residue by a protein kinase

Question 12

Which of the following statements about ribozymes is CORRECT?

Accepted Answer

Ribozymes are RNA molecules with catalytic activity, such as self-splicing of RNA.

Question 13

A researcher measures the initial velocity ($$v) of an $$enzyme-catalyzed reaction at various substrate concentrations. She finds that when $$[S] = K_m$$, the velocity is:

Accepted Answer

$$v = \frac{1}{2} V_{max}$$

Question 14

Which of the following is a real-life example of feedback inhibition?

Accepted Answer

The end product of a metabolic pathway inhibits an enzyme that acts early in the pathway.

Question 15

Which of the following best describes 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 16

Which of the following is TRUE about allosteric enzymes?

Accepted Answer

They have separate active and allosteric sites, and can be regulated by allosteric effectors.

Question 17

Which of the following is the correct Michaelis–Menten equation for enzyme kinetics?

Accepted Answer

$$v = \frac{V_{max} [S]}{K_m + [S]}$$

Question 18

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

Accepted Answer

They increase the rate at which equilibrium is achieved without changing the position of equilibrium.

Question 19

A mutation in an enzyme's active site changes a key amino acid from aspartate (Asp) to alanine (Ala). What is the most likely effect?

Accepted Answer

The enzyme's substrate specificity and catalytic activity may be reduced or lost.

Enzymes: The Catalysts of Life – Comprehensive Study Notes

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