Fundamentals Of Biochemistry Life At The Molecular Level 4th Edition By Donald Voet – Test Bank

41. Enzyme X catalyzes the addition of a hydroxyl group to substrate Y. In the process a metal cofactor is reduced and then reoxidized. What class of enzyme is X?

A) oxidoreductase
B) ligase
C) hydrolase
D) isomerase
E) lyase

Ans: A
Level of Difficulty: Easy
Section: 11.1.A and B
Learning objective: General Properties of Enzymes

42. The transition state of an enzyme and substrate reaction

A) must always bind the enzyme active site with lower energy than the products.
B) is stabilized by enhancing the reverse reaction of E + S→ES.
C) is composed of true covalent bonds which decrease its energy.
D) is stabilized due to the specificity of the active site for the substrate.
E) is stabilized by decreasing the effective concentration.

Ans: D
Level of Difficulty: Moderate
Section: 11.2
Learning objective: Activation Energy and the Reaction Coordinate

43. Proximity effects

A) result from active site specificity.
B) result from substrate channeling.
C) result in increased effective concentration of substrate.
D) lower the energy of activation.
E) All of the above of the above are correct.

Ans: D
Level of Difficulty: Difficult
Section: 11.3.D
Learning objective: Catalytic Mechanisms

44. In the serine protease trypsin, the specificity for one substrate over another describes what type of catalysis?

A) proximity
B) acid-base
C) covalent
D) strain
E) none of the above

Ans: A
Level of Difficulty: Moderate
Section: 11.5.A, B, C
Learning objective: Serine Proteases

45. Which type of catalysis may be carried out using redistribution of electron density to facilitate the transfer of a proton?

I. proximity
II. acid-base
III. covalent
IV. strain

A) I
B) II
C) III
D) II, III
E) II, IV

Ans: D
Level of Difficulty: Difficult
Section: 11.3.B
Learning objective: Catalytic Mechanisms

46. In trypsin the specificity for one substrate over another comes from

A) the negatively charged pocket.
B) the positively charge pocket.
C) the hydrophobic pocket.
D) the amino acid serine.
E) the amino acid histidine.

Ans: A
Level of Difficulty: Easy
Section: 11.5.A, B, C

47. Which of the following is TRUE regarding transition state?

A) The free energy between the transition state and the reactants must be negative.
B) The transition state can be stabilized by covalent catalysis.
C) The transition state represents the ES complex.
D) Transition state analogs bind the substrate not the enzyme
E) All of the above are true.

Ans: B
Level of Difficulty: Moderate
Section: 11.2
Learning objective: Activation Energy and the Reaction Coordinate

48. Research scientists are trying to clone a gene. In order to accomplish this task they join two pieces of DNA. Which class of the enzymes below might accomplish this task?

A) oxidoreductase
B) ligase
C) hydrolase
D) isomerase
E) lyase

Ans: B
Level of Difficulty: Moderate
Section: 11.1.A
Learning objective: General Properties of Enzymes

50. Why can histidine NOT act as a base in the lysosome (an organelle where the pH is close to 4.5)?

A) Histidine has a positive charge at pH 4.5.
B) Histidine has a side chain pK close to 6.
C) Histidine would be protonated at pH 4.5.
D) All of the above are correct.
E) None of the above is correct.

Ans: D
Level of Difficulty: Moderate
Section: 11.3.A
Learning objective: Catalytic Mechanisms

53. Acid-base catalysis may be accomplished by:

A) active site specificity
B) charge delocalization
C) buffer effects
D) induced strain
E) conformational change

Ans: B
Level of Difficulty: Difficult
Section: 11.3.A
Learning objective: Catalytic Mechanisms