Lehninger Principles of Biochemistry 6th Edition By David L. Nelson – Test Bank
Chapter 6 Enzymes
Multiple Choice Questions
1. An introduction to enzymes
Pages: 183184 Difficulty: 1 Ans: A
One of the enzymes involved in glycolysis, aldolase, requires Zn2+ for catalysis. Under conditions of zinc deficiency, when the enzyme may lack zinc, it would be referred to as the:
A) apoenzyme.
B) coenzyme.
C) holoenzyme.
D) prosthetic group.
E) substrate.
2. An introduction to enzymes
Page: 185 Difficulty: 1 Ans: D
Which one of the following is not among the six internationally accepted classes of enzymes?
A) Hydrolases
B) Ligases
C) Oxidoreductases
D) Polymerases
E) Transferases
3. How enzymes work
Pages: 186187 Difficulty: 2 Ans: E
Enzymes are potent catalysts because they:
A) are consumed in the reactions they catalyze.
B) are very specific and can prevent the conversion of products back to substrates.
C) drive reactions to completion while other catalysts drive reactions to equilibrium.
D) increase the equilibrium constants for the reactions they catalyze.
E) lower the activation energy for the reactions they catalyze.
4. How enzymes work
Pages: 186187 Difficulty: 1 Ans: D
The role of an enzyme in an enzyme-catalyzed reaction is to:
A) bind a transition state intermediate, such that it cannot be converted back to substrate.
B) ensure that all of the substrate is converted to product.
C) ensure that the product is more stable than the substrate.
D) increase the rate at which substrate is converted into product.
E) make the free-energy change for the reaction more favorable.
5. How enzymes work
Pages: 186188 Difficulty: 2 Ans:D
Which one of the following statements is true of enzyme catalysts?
A) Their catalytic activity is independent of pH.
B) They are generally equally active on D and L isomers of a given substrate.
C) They can increase the equilibrium constant for a given reaction by a thousand fold or more.
D) They can increase the reaction rate for a given reaction by a thousand-fold or more.
E) To be effective, they must be present at the same concentration as their substrate.
6. How enzymes work
Pages: 186188 Difficulty: 2 Ans: D
Which one of the following statements is true of enzyme catalysts?
A) They bind to substrates but are never covalently attached to substrate or product.
B) They increase the equilibrium constant for a reaction, thus favoring product formation.
C) They increase the stability of the product of a desired reaction by allowing ionizations, resonance, and isomerizations not normally available to substrates.
D) They lower the activation energy for the conversion of substrate to product.
E) To be effective, they must be present at the same concentration as their substrates.
7. How enzymes work
Pages: 186188 Difficulty: 1 Ans: C
Which of the following statements is false?
A) A reaction may not occur at a detectable rate even though it has a favorable equilibrium.
B) After a reaction, the enzyme involved becomes available to catalyze the reaction again.
C) For S P, a catalyst shifts the reaction equilibrium to the right.
D) Lowering the temperature of a reaction will lower the reaction rate.
E) Substrate binds to an enzyme’s active site.
8. How enzymes work
Pages: 189190 Difficulty: 1 Ans: B
Enzymes differ from other catalysts in that only enzymes:
A) are not consumed in the reaction.
B) display specificity toward a single reactant.
C) fail to influence the equilibrium point of the reaction.
D) form an activated complex with the reactants.
E) lower the activation energy of the reaction catalyzed.
9. How enzymes work
Page: 190 Difficulty: 2 Ans: A
Compare the two reaction coordinate diagrams below and select the answer that correctly describes their relationship. In each case, the single intermediate is the ES complex.
A) (a) describes a strict “lock and key” model, whereas (b) describes a transition-state complementarity model.
B) The activation energy for the catalyzed reaction is 5 in (a) and is 7 in (b).
C) The activation energy for the uncatalyzed reaction is given by 5 + 6 in (a) and by 7 + 4 in (b).
D) The contribution of binding energy is given by 5 in (a) and by 7 in (b).
E) The ES complex is given by 2 in (a) and 3 in (b).
10. How enzymes work
Pages: 190191 Difficulty: 2 Ans: B
Which of the following is true of the binding energy derived from enzyme-substrate interactions?
A) It cannot provide enough energy to explain the large rate accelerations brought about by enzymes.
B) It is sometimes used to hold two substrates in the optimal orientation for reaction.
C) It is the result of covalent bonds formed between enzyme and substrate.
D) Most of it is derived from covalent bonds between enzyme and substrate.
E) Most of it is used up simply binding the substrate to the enzyme.
Reviews
There are no reviews yet.