Biochem: Chapter 8 Questions

For a reaction A→B in which [A] eq = 0.6 M, [B] eq = 0.4 M, [A] = 0.7 M, and [B] = 0.3 M, the sign of ΔG and ΔG°′ are, respectively: A) negative; positive B) negative; negative C) positive; zero D) positive; positive E) positive; negative

A

Enzymes enhance the rate of a reaction by _____ the free energy of the _____. A) lowering; transition state B) raising; transition state C) lowering; reactants D) raising; reactants E) raising; products

A

Enzymes: A) accelerate the forward and reverse reactions equally. B) increase the equilibrium constant for the reaction. C) lower the value of ΔG. D) accelerate the forward reaction only. E) increase the value of ΔG.

A

A noncompetitive inhibitor is added at a concentration equal to its own K(sub)i. When the V(sub)0 vs. [S] plot is obtained, it will be observed that the V(sub)0 in the presence of inhibitor compared to the V(sub)0 in the absence of inhibitor will be: A) one-half at all concentrations. B) one-half at Vmax and less than one-half at lower [S]. C) one-half at Vmax and more than one-half at lower [S]. D) two-thirds at Vmax and less than two-thirds at lower [S]. E) two-thirds at all concentrations.

A

Calculate the ΔG° ′ for a reaction of A→B that has a K ′ eq of 0.082 at a temperature of 298 K. A) 6.2 kJ mol ^—1 B) —6.2 kJ mol ^—1 C) —0.52 kJ mol ^—1 D) 6.2 kcal mol ^—1 E) There is not enough information provided to determine the answer.

A

The K(sub)M of an enzyme is 20 mM. At a [S] of 30 mM, what percentage of the enzyme has substrate bound to it? A) 60% B) 50% C) 40% D) 33% E) 75%

A

Which of the following is a possible unit for K(sub)M? A) mM B) s C) s^-1 D) mM^-1 E) mM⁄s

A

A 1 × 10^-=—5 M concentration of an enzyme with a K(sub)M of 10 mM gives a rate of 1.0 × 10^—3 M/s when the [S] is 40 mM. The value of k(sub)cat would be: A) 1.0 × 10^—8 s^—1. B) 4.0 × 10^—3 M/s. C) 4.0 × 10^2 s^—1. D) 1.25 × 10^—3 M/s. E) 1.25 × 10^2 s^—1.

A 1 × 10^-=—5 M concentration of an enzyme with a K(sub)M of 10 mM gives a rate of 1.0 × 10^—3 M/s when the [S] is 40 mM. The value of k(sub)cat would be: E) 1.25 × 10^2 s^—1

An Eadie Hofstee diagram plots V(sub)0 vs. (V(sub)0/[S]). For such a plot, the slope of the straight line will be: A) V(sub)max B) K(sub)M C) -K(sub)M D) K(sub)M/V(sub)max E) V(sub)max/K(sub)M

An Eadie Hofstee diagram plots V(sub)0 vs. (V(sub)0/[S]). For such a plot, the slope of the straight line will be: C) -K(sub)M

An enzyme catalyzes the reaction of A↔B. At 25° C, otherwise known as 298 K, the ΔG of the reaction is —1.3 kcal mol^—1 and ΔG° ′ is +1.2 kcal mol ^—1. Which of the following statements would be CORRECT if the enzyme is removed? A) Keq will be smaller. B) Keq will stay the same. C) The reaction will no longer be thermodynamically favorable and B will not be produced. D) The equilibrium constant of the forward reaction will decrease. E) Both the first and fourth answers are correct.

B

An enzyme speeds up a reaction by 10^5; by approximately how many kcal⁄mol of energy does the enzyme stabilize the transition state? A) 1. 4 kcal⁄mol B) 6.8 kcal⁄mol C) 3.5 kcal⁄mol D) 5.0 kcal⁄mol E) 10 kcal⁄mol

B

Determine the K(sub)M and V(sub)max for an enzyme that yields the following kinetic data: [IMAGE] A) K(sub)M = 55 mM; V(sub)max = 0.6 M⁄min B) K(sub)M = 0.5 mM; V(sub)max = 55 mM⁄min C) K(sub)M = 0.5 mM; V(sub)max = 25 mM⁄min D) K(sub)M = 0.01 mM ; V(sub)max = 55 mM⁄min E) There is not enough information given to determine K(sub)M and V(sub)max.

B

When [S] = K(sub)M: A) V(sub)0 = V(sub)max/2 B) [E] = [ES] C) V(sub)0 is linear with respect to [S] D) Both the first and second answers are correct E) Both the second and third answers are correct

D

The K(sub)i of a noncompetitive enzyme inhibitor is 10 μM. At a 5 μM concentration of this inhibitor, the apparent V(sub)max would be: A) approximately 50% of the uninhibited V(sub)max. B) approximately 67% of the uninhibited V(sub)max. C) approximately 150% of the uninhibited V(sub)max. D) approximately 33% of the uninhibited V(sub)max. E) unchanged.

B

The affinity label bromoacetol phosphate inhibits triose phosphate isomerase because it: A) is group-specific for Glu residues. B) resembles the substrate. C) is a suicide inhibitor. D) Both the first and second answers are correct. E) Both the first and third answers are correct.

B

The slope of a double-reciprocal (Lineweaver-Burk) plot increases by 20% in the presence of a 10 μM concentration of a competitive inhibitor. What is the value of K(sub)i? A) 25 μM B) 50 μM C) 10 μM D) 2 μM E) 5 μM

B

Two enzymes (called E1 and E2) catalyze the exact same reaction: A → B The only difference between the two enzymes is in their K(sub)M value. An experiment is carried out as follows. Two sets of reaction tubes are prepared that contain identical amounts of substrate A (5 mM, 10 mM, and 15 mM). Enzyme E1 is added to the first set of tubes and an identical amount of enzyme E2 is added to the second set of tubes at the same time under identical conditions. Results of the first experiment are shown in the following plot with E1 giving the red line and E2 the black line. [IMAGE] A) The enzyme from species #1 has a larger maximum velocity than the enzyme from species #2. B) The enzyme from species #2 has a larger maximum velocity than the enzyme from species #1. C) The enzyme from species #1 has a higher affinity for the substrate. D) The enzyme from species #2 has a higher affinity for the substrate. E) None of the above

B

Two enzymes that catalyze the same reaction were isolated from two different species. In this Lineweaver-Burk plot, the kinetic results of identical concentrations of the two enzymes are shown. The data indicated with red were obtained for the enzyme isolated from species #1, while the data in black were obtained for the enzyme isolated from species #2. Which of the following is TRUE given these data? [IMAGE] A) The enzyme from species #1 has a larger maximum velocity than the enzyme from species #2. B) The enzyme from species #2 has a larger maximum velocity than the enzyme from species #1. C) The enzyme from species #1 has a higher affinity for the substrate. D) The enzyme from species #2 has a higher affinity for the substrate. E) None of the above.

B

Which of the following is true of a second-order reaction but not true of a first-order reaction? A) the rate of the reaction is proportional to a constant (k) B) it involves at least two substrates C) it involves at least two products D) it involves at least two transition states E) All of the above

B

Which of the following statements is TRUE? A) Enzyme E1 has a higher affinity for the substrate than enzyme E2. B) Enzyme E2 has a higher affinity for the substrate than enzyme E1. C) Enzyme E1 has a larger V(sub)max than E2. D) Enzyme E2 has a larger V(sub)max than E1. E) It cannot be determined with the provided information.

B

A conformational change that occurs upon substrate binding opens up a pocket for an inhibitor to bind. The Lineweaver-Burk (double-reciprocal) plot of this enzyme in the presence and absence of this inhibitor would show: A) the same y-intercept with a different slope. B) no change in y-intercept or slope. C) the same slope with a different y-intercept. D) a linear behavior in the absence of inhibitor and nonlinear behavior in the presence of inhibitor. E) different y-intercepts and different slopes.

C

An enzyme lowers the apparent values of the V(sub)max and the K(sub)M. The enzyme is an example of a(n): A) irreversible inhibitor. B) competitive inhibitor. C) uncompetitive inhibitor. D) noncompetitive inhibitor. E) allosteric inhibitor.

C

An enzyme-substrate reaction is conducted under conditions where [S] = K(sub)M. A competitive inhibitor is added at a concentration equal to twice the K(sub)i for that inhibitor. To achieve a similar rate of reaction to the uninhibited reaction, you would: A) increase the amount of substrate by a factor of 1.5. B) double the amount of substrate. C) triple the amount of substrate. D) quadruple the amount of substrate. E) be unable to achieve the same rate observed originally.

C

An uncompetitive inhibitor increases the apparent value of: A) k(sub)—1 B) k(sub)2 C) k(sub)1 D) K(sub)M E) V(sub)max

C

When a _____ is added to an _____, a _____ is formed. A) cofactor; apoenzyme; coenzyme B) coenzyme; amphienzyme; holoenzyme C) cofactor; epienzyme; coenzyme D) cofactor; apoenzyme; holoenzyme E) coenzyme; apoenzyme; metaenzyme

D

Assume that rather than decreasing the free energy of the transition state for the reaction of S→X‡→P, a protein binds to S and increases the free energy of S to form a destabilized substrate (S*). S* can still undergo the reaction S*→X‡→P. In other words, it can attain the same transition state and form the same product as P. Which of the following are TRUE of this scenario? A) The protein is an enzyme that catalyzes only the reaction of X‡→P. B) The protein is an enzyme that catalyzes only the reaction of S→X‡. C) The protein increases the rate of the formation of P. D) The protein must also bind to P and form a destabilized species, P*. E) All of the above.

C

For a reaction A→B in which [A]eq = 0.2 M, [B] eq = 0.8 M, [A] = 0.5 M, and [B] = 0.5 M, the sign of ΔG and ΔG°′ are, respectively: A) positive; zero B) positive; negative C) negative; negative D) negative; positive E) positive; positive

C

Kinetic data obtained in the absence and presence of a noncompetitive inhibitor are plotted on a double-reciprocal plot. One line on the plot represents the data obtained in the absence of inhibitor, and one line on the plot represents the data obtained in the presence of the inhibitor. Which of the following would be TRUE? A) The slope of each line would be the same. B) The y-intercept of each line would be the same. C) The slope of the line representing the data obtained in the presence of inhibitor would be greater than the other line. D) The y-intercept of the line representing the data obtained in the presence of inhibitor would be lower than the y-intercept of the other line. E) Both the second and third answers are correct.

C

Roundup (glyphosate), when added to the enzyme it inhibits, would cause: A) no change in K(sub)M and decrease in V(sub)max. B) a complete inhibition whenever the inhibitor is in excess of the enzyme. C) a decrease in K(sub)M and decrease in V(sub)max. D) an increase in K(sub)M and no change in V(sub)max. E) an increase in K(sub)M and decrease in V(sub)max

C

The K(sub)M of an enzyme is 30 mM. When the [S] is increased from 10 mM to 20 mM, the value of V(sub)0 increases by: A) 33%. B) 50%. C) 60%. D) 80%. E) 100%.

C

The difference between ΔG° and ΔG°′ is that only the latter: A) assumes a 1 M concentration of everything. B) assumes a 1 atm concentration of gases. C) assumes a [H^+] of 1 x 10^—7 M. D) assumes a temperature of 298 K. E) None of the above.

C

The k(sub)un for the reaction that can be catalyzed by chorismate mutase is 2.6 × 10 ^—5 s (sub)—1, whereas the k(sub)cat is 50 s ^—1. What is the rate enhancement for this enzyme? A) There is not enough information provided to calculate the rate enhancement. B) 1.3 × 10 ^—3 C) 1.9 × 10^6 D) 5.2 × 10 ^—7 D) 50

C

The shape of a V(sub)0 vs. [S] for a Michaelis-Menten enzyme is: A) exponential. B) sigmoidal. C) hyperbolic. D) parabolic. E) linear.

C

The ΔG° is calculated by assuming the concentration of everything is 1.0 M except: A) products B) H^+ C) gases D) Both the second and third answers are correct E) All of the above are assumed to be at 1.0 M

C

Which of the following statements about binding energy is TRUE? A) The binding energy is proportional to the ΔG of the reaction being catalyzed by the enzyme. B) The change of free energy that takes place when substrate binds to the enzyme active site has to be larger than the ΔG‡ in order for catalysis to occur. C) The binding energy is lower in the ES complex than in the complex of the enzyme bound to the transition state of the reaction. D) The binding energy must be less than the overall ΔG for the enzyme-catalyzed reaction. E) None of the above.

C

Which of the following would lower the apparent K(sub)M of an enzyme-substrate reaction? A) irreversible inhibitor B) competitive inhibitor C) uncompetitive inhibitor D) noncompetitive inhibitor E) More than one of these is correct.

C

An enzyme catalyzes a reaction that is inhibited by inhibitor Q. Below is a plot obtained for this enzyme-catalyzed reaction in the absence and presence of 0.5 mM inhibitor Q. [IMAGE] Which of the following is TRUE? A) Q is a competitive inhibitor. B) Q is an uncompetitive inhibitor. C) Q can combine with only the ES complex. D) Q can combine with both E and the ES complex. E) Q is an irreversible inhibitor.

D

Consider the reaction A + B ↔C + D. At biochemical equilibrium (25° C, pH of 7), the concentration of A is 0.2 M, the concentration of B is 0.2M, the concentration of C is 0.8M, and the concentration of D is 0.8M. Calculate ΔG and ΔG° ′ under these conditions. A) ΔG = —6.86 kJ mol —1; ΔG° ′ = +6.86 kJ mol —1 B) ΔG = 0 kJ mol —1; ΔG° ′ = 16 kJ mol —1 C) ΔG = —6.86 kJ mol —1; ΔG° ′ = 0 kJ mol — D) ΔG = 0 kJ mol —1; ΔG° ′ = —6.86 kJ mol —1 E) There is not enough information provided to determine the answer.

D

For a reaction A → B in which [A]eq = 0.8 M, [B]eq = 0.2 M, [A] = 0.7 M, and [B] = 0.3 M, the sign of ΔG and ΔG°′ are, respectively: A) negative; positive. B) positive; zero. C) positive; negative. D) positive; positive. E) negative; negative.

D

From a Lineweaver-Burk plot, the value of K(sub)M could be determined by: A) (1⁄x-intercept). B) (slope)( y-intercept). C) (slope) ⁄ (y=x-intercept). D) (slope) ⁄ (y-intercept). E) (1⁄y-intercept).

D

People who are more sensitive to ethanol have a less active _____ enzyme, which normally has the _____ K(sub)M value. A) liver; lower B) cytoplasmic; lower C) cytoplasmic; higher D) mitochondrial; lower E) mitochondrial; higher

D

The K(sub)i for a competitive inhibitor is 10 μM. At a concentration of 40 μM, what percentage of the enzyme is bound to inhibitor? A) 25% B) 75% C) 40% D) 80% E) 50%

D

The Michaelis-Menten equation indicates that the reaction order is approximately zero for S: A) throughout the range of [S] B) when [S] < < K(sub)M C) when [S] = K(sub)M D) when [S] > > K(sub)M E) never

D

The kinetics of an enzyme-catalyzed reaction can be altered in the presence of an inhibitor. Which of the following is a way that the kinetics can be altered? A) The K(sub)M can be decreased by a noncompetitive inhibitor. B) The K(sub)M can be increased by an uncompetitive inhibitor. C) The V(sub)max can be increased by a competitive inhibitor. D) The V(sub)max can be decreased by a noncompetitive inhibitor. E) None of the above.

D

When [S] = 10 K(sub)M, what percentage of V(sub)max is V(sub)0? A) 80% B) 99% C) 95% D) 91% E) 70%

D

Certain enzymes have a "fast equilibrium" in which the rate of product formation is much slower than ES dissociation to E + S. Under these conditions: A) K(sub)M is effectively a binding constant. B) K(sub)M is approximately equal to k(sub)2⁄k(sub)1. C) K(sub)M is approximately equal to k(sub)-1⁄k(sub)1. D) Both the first and second answers are correct. E) Both the first and third answers are correct.

E

DIPF inhibits the enzyme acetylcholinesterase, revealing that the enzyme has a catalytically important: A) Phe B) His C) Arg D) Glu E) Ser

E

For a reaction A→B in which [A] eq = 0.3 M, [B] eq = 0.7 M, [A] = 0.1 M, and [B] = 0.9 M, the sign of ΔG and ΔG°′ are, respectively: A) positive; positive B) negative; negative C) negative; positive D) positive; zero E) positive; negative

E

If the ΔG° of a reaction of A → B is +7.53 kJ/mol and the [A] = 2 x 10^—4 M and [B] = 3 x 10^—6 M, the value of ΔG would be: A) 2.89 kJ⁄mol. B) 10.42 kJ⁄mol. C) 17.95 kJ⁄mol. D) —10.42 kJ⁄mol. E) —2.89 kJ⁄mol.

E

The K(sub)i of a competitive enzyme inhibitor is 2 μM. At a 4 μM concentration of this inhibitor, the apparent V(sub)max would be: A) approximately 67% of the uninhibited V(sub)max. B) approximately 50% of the uninhibited V(sub)max. C) approximately 33% of the uninhibited V(sub)max. D) approximately 200% of the uninhibited V(sub)max. E) unchanged.

E

The activation energy for a reaction is also known as: A) Gibbs free energy B) ΔG° ′ C) ΔG° D) ΔG E) None of the above

E

The study of the rates of enzyme-catalyzed reaction: A) is called enzyme kinetics. B) can involve determining how fast the substrate disappears as it is converted to product. C) can involve following the appearance of product formed over time. D) usually appears to be a first order reaction despite the fact that it is a bimolecular reaction. E) All of the above.

E

The ΔG°′ of a reaction of A → B is positive and the ΔG of the reaction is positive. Which of the following is definitely true? A) The reaction is spontaneous. B) The reaction is at equilibrium. C) [A] > [B]. D) [B] > [A]. E) None of these are definitely true.

E

This shows the reaction velocity versus substrate concentration in an enzyme-catalyzed reaction. Which of the following statements is TRUE? [IMAGE] A) This plot indicates that a discrete ES complex exists. B) This plot indicates that the enzyme active site becomes saturated at high concentrations of substrate. C) In the absence of enzyme, this plot would be linear, not hyperbolic. D) This plot indicates that at low substrate concentrations, enzyme velocity is highly dependent on substrate concentration. E) All of the above.

E

Which of the following is TRUE of a graph of velocity versus [S] in which the data were obtained when enzyme was added to the system? A) It would be an inverse parabola B) It would be a Lineweaver-Burke plot C) The equation describing the resulting plot would be in the form of y = mx + b D) It would allow for the determination of k(sub)-1 of the enzyme E) None of the above

E

Which of the following is TRUE? A) The ΔG of a reaction is always lower than the ΔG°. B) The standard free-energy change, ΔG°, is determined when all reactants, except hydrogen ion, are at 1M. C) At equilibrium, the ΔG° is zero. D) Both the first and second answers are correct. E) None of the above.

E

Which of the following is a reversible inhibitor? A) diisopropylphosphofluoridate, a group-specific reagent that reacts with serine residues B) tosyl-L-phenylalanine chloromethyl ketone, a substrate analog for chymotrypsin that reacts with histidine residues C) penicillin, which forms an ester with serine residues of glycopeptides transpeptidase D) N,N-dimethylpropargylamine, a suicide inhibitor of monoamine oxidase E) None of the above.

E

Which of the following statements about enzyme active sites is CORRECT? A) Amino acids that are distant from each other in the primary sequence may come close together to form the active site. B) The microenvironment of active sites often excludes water. C) Interactions in the binding site may include weak interactions such as van der Waals, hydrogen bonds, electrostatic, and hydrophobic interactions. D) Polar residues in an active site often play very different roles than those found on the surface of a protein. E) All of the above.

E

Lineweaver-Burk plots have a y-intercept equal to: A) V(sub)max B) K(sub)M/V(sub)max C) 1/V(sub)max D) K(sub)M E) -1/K(sub)M

Lineweaver-Burk plots have a y-intercept equal to: C) 1/V(sub)max

The maximum value of k(sub)cat⁄K(sub)M is: A) V(sub)max B) K(sub)M C) k(sub)2 D) k(sub)—1 E) k(sub)1

The maximum value of k(sub)cat⁄K(sub)M is: E) k(sub)1

The ΔG°′ of a reaction of A → B is negative, and the ΔG of the reaction is positive. Which of the following is definitely true? A) The reaction is spontaneous. B) The reaction is at equilibrium. C) [A] > [B]. D) [B] > [A]. E) None of these are definitely true.

The ΔG°′ of a reaction of A → B is negative, and the ΔG of the reaction is positive. Which of the following is definitely true? D) [B] > [A]