Chapter 7

16) The catalytic constant, or kcat, is also known as the _____. A) turnover number B) saturation number C) catalytic efficiency number D) diffusion number E) Menten number

A

19) A Lineweaver-Burk plot is a _____. A) double reciprocal plot B) Michaelis-Menten plot C) sigmoidal plot D) hyperbolic plot E) logarithmic plot

A

23) 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

A

3) When a substrate and enzyme interact, the first chemical species formed is _____. A) enzyme-substrate complex B) enzyme-transition state complex C) enzyme-product complex D) enzyme plus product E) none of the above

A

32) A reversible inhibitor that binds to a site other than the active site regardless of whether or not the substrate is bound is a _____. A) noncompetitive inhibitor B) competitive inhibitor C) uncompetitive inhibitor D) allosteric inhibitor E) suicide substrate

A

35) How are the kinetics of an enzyme-catalyzed reaction affected by a mixed inhibitor? A) Vmax decreased, KM increased or decreased B) Vmax decreased, KM decreased C) Vmax decreased, KM increased D) Vmax unchanged, KM increased E) Vmax unchanged, KM increased or decreased

A

9) Which of the following properly expresses the Michaelis-Menten equation? A) vo = Vmax [S] / (KM + [S]) B) vo = Vmax KM / (KM + [S]) C) kcat = Vmax / [E]T D) Vmax = vo [S] / (KM + [S]) E) Vmax = vo KM / (KM + [S])

A

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

B

2) A plot of velocity versus substrate concentration for a simple enzyme-catalyzed reaction produces a _____. This indicates that at some point, the enzyme is _____. A) straight line; inhibited by product B) hyperbolic curve; saturated with substrate C) sigmoidal curve; inhibited by substrate D) hyperbolic curve; activated by substrate E) sigmoidal curve; saturated with substrate

B

25) Some irreversible inhibitors are called _____ because they bind to the active site of the enzyme and begin the catalytic process, just like a normal substrate. A) irreversible substrates B) suicide substrates C) noncompetitive substrates D) ping pong substrates E) allosteric substrates

B

29) 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

B

36) A reversible inhibitor that only affects multisubstrate enzymes and binds to the enzyme only after one substrate has bound is a _____. A) noncompetitive inhibitor B) uncompetitive inhibitor C) competitive inhibitor D) allosteric inhibitor E) suicide substrate

B

37) Which of the following types of inhibition can be reversed by addition of more substrate? A) noncompetitive inhibition B) competitive inhibition C) uncompetitive inhibition D) irreversible inhibition E) none of the above

B

8) The Michaelis constant is defined as _____. A) KM = k₂ / k₁ B) KM = (k₂ + k-₁) / k₁ C) KM = (k₂ - k-₁) / k₁ D) KM = (k₂ + k₁) / k-₁ E) KM = (k₂ - k₁) / k-₁

B

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

C

15) What is the kcat for a reaction in which Vmax is 0.4 mmoles/min and the reaction mixture contains 5 x 10-6 micromoles of enzyme? A) 2 x 10-14 min-1 B) 2 x 10-11 min-1 C) 8 x 107 min-1 D) 4 x 108 min-1 E) 8 x 109 min-1

C

18) An extremely efficient enzyme has a _____ KM and a _____ kcat. A) small; small B) small; large C) large; large D) large; small E) kcat and KM do nothing to predict the efficiency of an enzyme

C

21) If a Lineweaver-Burk plot gave a line with an equation of y = 0.25 x + 0.34, what are the values of KM and Vmax if the substrate concentration is in mM and the velocity in mM/s? A) 0.085 mM and 0.34 mM/s B) 2.9 mM and 0.023 mM/s C) 0.74 mM and 2.9 mM/s D) 0.37 mM and 1.4 mM/s E) 1.35 mM and .034 mM/s

C

24) 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

C

28) 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

C

33) How are the kinetics of an enzyme-catalyzed reaction affected by a purely noncompetitive inhibitor? A) Vmax decreased, KM increased B) Vmax decreased, KM decreased C) Vmax decreased, KM unchanged D) Vmax unchanged, KM increased E) Vmax unchanged, KM decreased

C

39) Which of the following represents a rapid and reversible mechanism to alter the activity of an enzyme? A) synthesis of more enzyme to increase activity B) degradation of enzyme to decrease activity C) covalent attachment of a phosphate group to increase or decrease activity D) movement of an enzyme from one cellular compartment to another E) none of the above

C

4) 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

C

10) When is KM considered to be the same as the dissociation constant for the ES complex i.e., KM ~ [E] [S] / [ES]. A) ES → E + P is fast compared to ES → E + S B) the turnover number is very large C) kcat/KM is near the diffusion-controlled limit D) k₂ << k-₁ E) KM can never be the same as the dissociation constant

D

12) If an enzyme-catalyzed reaction has a velocity of 2 mM/min and a Vmax of 10 mM/min when the substrate concentration is 0.5 mM, what is the KM? A) 0.2 mM B) 0.5 mM C) 1 mM D) 2 mM E) 5 mM

D

13) 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 ¾KM B) [S] must be 1.5KM C) [S] must be 2KM D) [S] must be 3KM E) [S] must be 4KM

D

20) If a Lineweaver-Burk plot gave a line with an equation of y = 0.490 x + 0.059, what is the velocity at a substrate concentration of 5 mM? The original units for substrate were in mM and velocity in mM/s. A) 0.288 mM/s B) 0.399 mM/s C) 2.51 mM/s D) 6.37 mM/s E) the velocity cannot be determined from this data

D

27) How are the kinetics of an enzyme-catalyzed reaction affected by a competitive inhibitor? A) Vmax decreased, KM increased B) Vmax decreased, KM decreased C) Vmax decreased, KM unchanged D) Vmax unchanged, KM increased E) Vmax unchanged, KM decreased

D

30) What does the KI for a competitive inhibitor mean? A) higher KI values mean tighter binding to ES complex B) lower KI values mean tighter binding to ES complex C) higher KI values mean tighter binding to the enzyme D) lower KI values mean tighter binding to the enzyme E) KI values tell nothing about inhibitor binding

D

34) 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

D

6) Which of the following expresses the velocity for an enzyme-catalyzed reaction that obeys Michaelis-Menten kinetics? A) v = k₁[E][S] B) v = k₁[E][S] - k⁻₁[ES] C) v = k₁[E][S] + k₂[ES] D) v = k₂[ES] E) v = k₂[ES] - k-₁[ES]

D

14) If an enzyme-catalyzed reaction with a KM of 3.5 mM has a velocity of 5 mM/min at a substrate concentration of 0.5 mM, what is the Vmax? A) 0.625 mM/min B) 15 mM/min C) 17.5 mM/min D) 35 mM/min E) 40 mM/min

E

17) Which of the following indicates that an enzyme has evolved to its most efficient form? A) kcat is a large number B) KM is a small number C) KM is a large number D) kcat/KM is a small number E) kcat/KM is near the diffusion-controlled limit

E

22) 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

E

26) An inhibitor that binds to the active site only in the absence of the substrate and in a reversible fashion is a(n) _____. A) allosteric inhibitor B) suicide substrate C) mixed inhibitor D) noncompetitive inhibitor E) competitive inhibitor

E

31) 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

E

38) Which of the following statements regarding allosteric enzymes is true? A) they are always oligomeric B) they are generally found at regulatory sites in metabolic pathways C) they are subject to regulation by both positive and negative effectors D) a plot of velocity versus [substrate] often yields a sigmoidal curve E) all of the above

E

5) For a reaction A + B → 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

E

7) Which of the following must be true if the steady state assumption is to be used? A) [E]T = [ES] B) (k₂ - k-₁) / k₁ = 1 C) k₁[E][S] = k₂[ES] D) k₁[E][S] = k₂[ES] - k-₁[ES] E) d[ES] / dt = 0

E