Biochemistry I Chem 471
Chapter 6  Quiz Preview	Enzymes
Multiple Choice Questions

1. 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. 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. 

3. 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. 

4. 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. 

5. The benefit of measuring the initial rate of a reaction V0 is that at the beginning of a reaction: 
  A.  [ES] can be measured accurately. 
  B.  changes in [S] are negligible, so [S] can be treated as a constant. 
  C.  changes in Km are negligible, so Km can be treated as a constant. 
  D.  V0 = Vmax. 
  E.  varying [S] has no effect on V0. 

6. The steady state assumption, as applied to enzyme kinetics, implies: 
  A.  Km = Ks. 
  B.  the enzyme is regulated. 
  C.  the ES complex is formed and broken down at equivalent rates. 
  D.  the Km is equivalent to the cellular substrate concentration. 
  E.  the maximum velocity occurs when the enzyme is saturated. 

7. An enzyme-catalyzed reaction was carried out with the substrate concentration initially a thousand times greater than the Km for that substrate.  After 9 minutes, 1% of the substrate had been converted to product, and the amount of product formed in the reaction mixture was 12 _mol.  If, in a separate experiment, one-third as much enzyme and twice as much substrate had been combined, how long would it take for the same amount (12 _mol.)  of product to be formed? 
  A.  1.5 min 
  B.  13.5 min 
  C.  27 min 
  D.  3 min 
  E.  6 min 


8. The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics:

	  Vo          Substrate added
  (micromol)/min.  (mmol)/L. 
  --------------  ---------------
	  217             0.8
	  325             2
	  433             4
	  488             6
	  647             1,000
  --------------  ---------------
  
The Km for this enzyme is approximately: 
  A.  1 mM. 
  B.  1,000 mM. 
  C.  2 mM. 
  D.  4 mM. 
  E.  6 mM. 

9. The number of substrate molecules converted to product in a given unit of time by a single enzyme molecule at saturation is referred to as the: 
  A.  dissociation constant. 
  B.  half-saturation constant. 
  C.  maximum velocity. 
  D.  Michaelis-Menten number. 
  E.  turnover number. 

10. A good transition-state analog: 
  A.  binds covalently to the enzyme. 
  B.  binds to the enzyme more tightly than the substrate. 
  C.  binds very weakly to the enzyme. 
  D.  is too unstable to isolate. 
  E.  must be almost identical to the substrate.