Question 1

Which of the following best explains why not all exergonic reactions occur spontaneously in living cells, even though they have a negative $$\Delta G$$?

Accepted Answer

The activation energy ($$E_a) $$barrier must be overcome for the reaction to proceed.

Question 2

What is the primary effect of an enzyme on the activation energy ($$E_a) of a $$reaction?

Accepted Answer

It lowers the activation energy by stabilizing the transition state.

Question 3

Which statement about catalysts is CORRECT?

Accepted Answer

They change the rate at which equilibrium is achieved, but not the position of equilibrium.

Question 4

Which of the following is a unique property of enzymes compared to non-biological catalysts?

Accepted Answer

They have remarkable specificity for their substrates.

Question 5

The induced fit model of substrate binding suggests that:

Accepted Answer

The enzyme changes conformation to bind the substrate more tightly and facilitate catalysis.

Question 6

Which of the following is NOT a mechanism by which the active site of an enzyme can activate a substrate?

Accepted Answer

Increasing the temperature of the substrate.

Question 7

Which of the following best describes competitive inhibition?

Accepted Answer

The inhibitor binds to the active site, preventing substrate binding.

Question 8

A drug acts as a noncompetitive inhibitor of an enzyme. Which of the following kinetic changes would you expect?

Accepted Answer

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

Question 9

Which equation describes the relationship between initial velocity ($$v$$), substrate concentration ($$[S]$$), maximum velocity ($$V_{max}$$), and Michaelis constant ($$K_m$$)?

Accepted Answer

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

Question 10

If an enzyme has a low $$K_m$$ for its substrate, what does this indicate?

Accepted Answer

The enzyme has a high affinity for the substrate.

Question 11

Which of the following is an example of regulation by covalent modification?

Accepted Answer

Phosphorylation of glycogen phosphorylase by a kinase.

Question 12

What is the role of zymogens in enzyme regulation?

Accepted Answer

They are inactive precursors that require proteolytic cleavage for activation.

Question 13

Which of the following best describes feedback inhibition?

Accepted Answer

The end product of a pathway inhibits an earlier enzyme in the pathway.

Question 14

Which of the following statements about allosteric enzymes is TRUE?

Accepted Answer

They are usually composed of multiple subunits and can be regulated by effectors binding at sites other than the active site.

Question 15

A patient is given a drug that acts as a competitive inhibitor for an essential enzyme. Which of the following changes would you expect in the enzyme kinetics?

Accepted Answer

$$K_m$$ increases, $$V_{max}$$ remains unchanged.

Question 16

Which of the following is a real-life example of enzyme specificity?

Accepted Answer

Trypsin cleaves peptide bonds after lysine or arginine residues.

Question 17

Which of the following best describes the effect of temperature on enzyme activity?

Accepted Answer

Each enzyme has an optimal temperature at which its activity is maximal.

Question 18

Which of the following is the correct Lineweaver-Burk (double-reciprocal) equation for enzyme kinetics?

Accepted Answer

$$\frac{1}{v} = \frac{K_m}{V_{max}} \frac{1}{[S]} + \frac{1}{V_{max}}$$

Question 19

Which of the following is a consequence of enzyme cooperativity?

Accepted Answer

Binding of one substrate molecule increases the affinity of other subunits for the substrate.

Enzymes: The Catalysts of Life – Mechanisms, Regulation, and Kinetics

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