Deck 7: Enzyme Kinetics and Inhibition

Question 1

Which of the following is true about enzymes?

A) enzymes show very little specificity for their substrates
B) enzymes catalyze reactions in only one direction
C) enzyme activities can often be regulated
D) enzymes reaction rates are generally slower than other chemical catalysts
E) enzymes operate under a wide range of temperatures and pH

Answer 1

enzyme activities can often be regulated

Question 2

How is an enzyme-catalyzed reaction affected by the addition of more enzyme?

A) velocity is not effected
B) velocity will increase only if more substrate is also added
C) velocity will increase
D) velocity will decrease
E) none of the above

Answer 2

velocity will increase

Question 3

For a reaction A + B $\rarr$ C, if [B] is much larger than [A] so that [B] essentially remains constant over the course of the reaction, the kinetics will be _____.

A) zero-order
B) hyperbolic
C) first-order
D) sigmoidal
E) pseudo first-order

Answer 3

pseudo first-order

Question 4

Which of the following properly expresses the Michaelis-Menten equation?

A) v_o = V_max [S] / (K_M + [S])
B) v_o = V_max K_M / (K_M + [S])
C) k_cat = V_max / [E]_T
D) V_max = v_o [S] / (K_M + [S])
E) V_max = v_o K_M / (K_M + [S])

Question 5

When is K_M considered to be the same as the dissociation constant for the ES complex i.e., K_M $\approx$ [E] [S] / [ES].

A) ES $\rarr$ E + P is fast compared to ES $\rarr$ E + S
B) the turnover number is very large
C) k_cat/K_M is near the diffusion-controlled limit
D) k₂ << k_-1
E) K_M can never be the same as the dissociation constant

Question 6

What percentage of V_max is obtained when the substrate is present at ¼ of the K_M?
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A) 5%
B) 20%
C) 25%
D) 80%
E) 100%

Question 7

Which of the following must be true for an enzymatic reaction obeying the Michaelis-Menten equation to reach 3/4 of its maximum velocity?

A) [S] must be ¾K_M
B) [S] must be 1.5K_M
C) [S] must be 2K_M
D) [S] must be 3K_M
E) [S] must be 4K_M

Question 8

Which of the following types of enzyme-catalyzed reactions follows non-Michaelis-Menten kinetics?

A) bisubstrate reactions with a random mechanism
B) bisubstrate reactions with a ping pong mechanism
C) bisubstrate reactions with an ordered mechanism
D) allosteric enzyme reactions
E) all of the above

Question 9

In a bisubstrate reaction, reactant A binds, followed by reactant B which then get converted to products C and D. An experiment showed that B cannot bind without A having bound first. What mechanism is indicated by this data?

A) ordered mechanism
B) random mechanism
C) ping pong mechanism
D) cooperative mechanism
E) none of the above

Question 10

In a bisubstrate reaction, reactant A binds and is then converted to product C. Next, reactant B binds and is then converted to product D. An experiment showed that B cannot bind without C being released first. What mechanism is indicated by this data?

A) ordered mechanism
B) random mechanism
C) ping pong mechanism
D) cooperative mechanism
E) none of the above

Question 11

How are the kinetics of an enzyme-catalyzed reaction affected by a competitive inhibitor?

A) V_max decreased, K_M increased
B) V_max decreased, K_M decreased
C) V_max decreased, K_M unchanged
D) V_max unchanged, K_M increased
E) V_max unchanged, K_M decreased

Question 12

If a Lineweaver-Burk plot was made for an enzyme-catalyzed reaction, both with and without a competitive inhibitor present, what difference would be seen?

A) the y-intercept would be lower for the inhibited reaction
B) the y-intercept would be higher for the inhibited reaction
C) the slope would be less for the inhibited reaction
D) the slope would be greater for the inhibited reaction
E) none of the above

Question 13

What type of inhibition explains why even at very high substrate concentrations, enzyme activity will decrease as time increases?

A) allosteric inhibition
B) product inhibition
C) transition state analogs
D) irreversible inhibition
E) uncompetitive inhibition

Question 14

Which of the following is true regarding transition state analogs?

A) they are competitive inhibitors
B) they bind to an active site with much higher affinity than most inhibitors
C) they are much more stable than the transition state
D) their affinity for an enzyme is often much greater that the substrate
E) all of the above

Question 15

How are the kinetics of an enzyme-catalyzed reaction affected by a purely noncompetitive inhibitor?

A) V_max decreased, K_M increased
B) V_max decreased, K_M decreased
C) V_max decreased, K_M unchanged
D) V_max unchanged, K_M increased
E) V_max unchanged, K_M decreased

Question 16

If a Lineweaver-Burk plot was made for an enzyme-catalyzed reaction, both with and without a noncompetitive inhibitor present, what difference would be seen?

A) the y-intercept would be higher with slope unchanged for the inhibited reaction
B) the y-intercept would be lower with larger slope for the inhibited reaction
C) the y-intercept would be lower with smaller slope for the inhibited reaction
D) the y-intercept would be higher with larger slope for the inhibited reaction
E) the y-intercept would be higher with smaller slope for the inhibited reaction

Question 17

How are the kinetics of an enzyme-catalyzed reaction affected by a mixed inhibitor?

A) V_max decreased, K_M increased or decreased
B) V_max decreased, K_M decreased
C) V_max decreased, K_M increased
D) V_max unchanged, K_M increased
E) V_max unchanged, K_M increased or decreased

Question 18

Acyclovir is an analog of ___ that lacks interferes with ___.

Question 19

Find the initial velocity for an enzymatic reaction when V_max = 6.5 × 10^-5 mol•sec^-1, [S] = 3.0 × 10^-3 M, K_M = 4.5 × 10^-3 M, and the enzyme concentration at time zero is 1.5 × 10^-2 $\mu$ M.

A) 3.9 × 10^-5 mol•sec^-1
B) 2.6 × 10^-5 mol•sec^-1
C) 1.4 × 10^-2 mol•sec^-1
D) 8.7 × 10^-3 mol•sec^-1
E) Not enough information is given to make this calculation.

Question 20

The Michaelis constant KM is defined as _____.
I. (k-1 + k2)/k1
II. one-half Vmax
III. [S] = [ES]
IV. [ES]/2

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

Question 21

Find kcat for a reaction in which Vmax is 4 × 10-4 mol•min-1 and the reaction mixture contains one microgram of enzyme (the molecular weight of the enzyme is 200,000

A) 2 × 10-11 min-1
B) 8 × 107 min-1
C) 8 × 109 min-1
D) 2 × 10-14 min-1
E) 4 × 108 min-1