Chapter 6 Biochemistry

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:

• apoenzyme

• coenzyme

• holoenzyme

• prosthetic group

• substrate

Which one of the following is not among the six internationally accepted classes of enzymes?

• Hydrolases

• Ligases

  
  

• Oxidoreductase

• Polymerases

  
  

• Transferases

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.

  
  

Tags

NGSS.HS-PS1-5

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.

  
  

Tags

NGSS.HS-PS1-5

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.

  
  

Tags

NGSS.HS-PS1-5

The concept of “induced fit” refers to the fact that:

• A) enzyme specificity is induced by enzyme-substrate binding.

  
  

• B) enzyme-substrate binding induces an increase in the reaction entropy, thereby catalyzing the reaction.

  
  

• C) enzyme-substrate binding induces movement along the reaction coordinate to the transition state.

  
  

• D) substrate binding may induce a conformational change in the enzyme, which then brings catalytic

  groups into proper orientation

Which of these statements about enzyme-catalyzed reactions is false?

• A) At saturating levels of substrate, the rate of an enzyme-catalyzed reaction is proportional to the

  enzyme concentration

• B) If enough substrate is added, the normal Vmax of a reaction can be attained even in the presence of

  a competitive inhibitor.

• C) The rate of a reaction decreases steadily with time as substrate is depleted.

  
  

• D) The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but

  the equilibrium constant is more favorable in the enzyme-catalyzed reaction.

• E) The Michaelis-Menten constant Km equals the [S] at which V = 1/2 Vmax.

  
  

To calculate the turnover number of an enzyme, you need to know:

• A) the enzyme concentration.

  
  

• B) the initial velocity of the catalyzed reaction at [S] >> Km.

  
  

• C) the initial velocity of the catalyzed reaction at low [S].

  
  

• D) the Km for the substrate.

  
  

• E) both A and B.

  
  

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.

  
  

In competitive inhibition, an inhibitor:

• A) binds at several different sites on an enzyme.

  
  

• B) binds covalently to the enzyme.

  
  

• C) binds only to the ES complex.

  
  

• D) binds reversibly at the active site.

  
  

• E) lowers the characteristic Vmax of the enzyme.