Question 1

Which of the following best describes the primary role of enzymes in biological systems?

Accepted Answer

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

Question 2

Consider the reaction: $$C_6H_{12}O_6$ + 6 O_2$ ightarrow 6 CO_2$ + 6 H_2O + 	ext{Energy}. $$Which statement is correct regarding this process?

Accepted Answer

Glucose is oxidized and oxygen is reduced.

Question 3

Which of the following statements about the relationship between $$K'_{eq}$$ and $$\Delta G$$^{\circ'}$$ is correct?

Accepted Answer

$$K'_{eq} = 1$$ corresponds to $$\Delta G$$^{\circ'}$$ = 0$$

Question 4

Which of the following best explains why enzymes do not alter the equilibrium position of a reaction?

Accepted Answer

Enzymes accelerate both the forward and reverse reactions equally.

Question 5

A holoenzyme is best described as:

Accepted Answer

An enzyme with all necessary cofactors and coenzymes bound for activity.

Question 6

Which of the following is a correct classification for an enzyme that catalyzes the transfer of a phosphate group from ATP to glucose?

Accepted Answer

Transferase

Question 7

Which of the following best describes the concept of 'induced fit' in enzyme catalysis?

Accepted Answer

The enzyme changes conformation upon substrate binding to better accommodate the substrate.

Question 8

Which of the following statements about the binding energy ($$\Delta G_B) in $$enzyme catalysis is correct?

Accepted Answer

Binding energy is primarily derived from multiple weak non-covalent interactions optimized in the transition state.

Question 9

Which of the following is a key difference between catabolic and anabolic pathways?

Accepted Answer

Catabolic pathways are exergonic and release energy, anabolic pathways are endergonic and require energy.

Question 10

Which of the following amino acids is most likely to participate in general acid-base catalysis in an enzyme active site?

Accepted Answer

Histidine

Question 11

A reaction has a $$\Delta G$$^{\circ'}$$ of -17.1$ kJ/mol. What is the approximate value of K$$'_{eq}$$ at 25°C?

Accepted Answer

$$10^{3}$$

Question 12

Which of the following best explains why reactions far from equilibrium are common points of regulation in metabolic pathways?

Accepted Answer

They have large negative $$\Delta G$$ values and are essentially irreversible under cellular conditions.

Question 13

Which of the following is true regarding the effect of an enzyme on the activation energy and the overall free energy change of a reaction?

Accepted Answer

The enzyme lowers the activation energy but does not affect the overall free energy change ($$\Delta G).$$

Question 14

Which of the following best describes the role of a coenzyme in an enzymatic reaction?

Accepted Answer

A coenzyme is a non-protein organic molecule that transiently carries specific atoms or functional groups during the reaction.

Question 15

Which of the following is the correct equation relating the standard free energy change and the equilibrium constant?

Accepted Answer

$$\Delta G$$^{\circ'}$$ = -RT \ln K'_{eq}$$

Question 16

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

Accepted Answer

The active site of the enzyme forms multiple weak interactions that are optimized for the transition state of the substrate.

Question 17

Which of the following is an example of a reaction catalyzed by a hydrolase?

Accepted Answer

Cleavage of a peptide bond in a protein by addition of water

Question 18

Which statement best describes the effect of an enzyme that is complementary to the substrate (not the transition state)?

Accepted Answer

It binds the substrate tightly, but does not efficiently catalyze the reaction.

Question 19

Which of the following is a correct description of the role of the catalytic triad (Ser195, His57, Asp102) in serine proteases?

Accepted Answer

It provides a nucleophile, a general base, and an acid to facilitate peptide bond cleavage.

Enzymes: Catalysis, Mechanisms, and Energetics in Biochemistry

Study Guide - Practice Questions