Question 1

Enzyme active sites

Accepted Answer

A)  are nonspecific. 
B)  are a pocket or cleft. 
C)  always exclude water. 
D)  can only bind a single substrate at a time. 
A)  are nonspecific. 
B)  are a pocket or cleft. 
C)  always exclude water. 
D)  can only bind a single substrate at a time. B

Question 2

In vivo arginine decarboxylase activity is monitored over several days in the absence and presence of protease inhibitors. The activity is greatly reduced when protease inhibitors are present. Arginine decarboxylase is not a protease. Interpret these findings.

Accepted Answer

Arginine decarboxylase activity is regulated by proteolytic processing. When the proteases responsible for activating arginine decarboxylase are inhibited, the activity of arginine decarboxylase is reduced.

Question 3

If the rate constant for a reaction is determined to be equal to v / [Q][R], the reaction is the conversion of

Accepted Answer

A)  Q to R. 
B)  R to Q. 
C)  R plus Q to a product. 
D)  It is impossible to determine the reaction given the information provided. 
A)  Q to R. 
B)  R to Q. 
C)  R plus Q to a product. 
D)  It is impossible to determine the reaction given the information provided. C

Question 4

The conversion of L-proline to D-proline is shown below. Which of the following characteristics would most likely be found in a transition state analog that inhibits an enzyme that catalyzes the reaction?

Accepted Answer

A)  planar 
B)  positively charged at the $\alpha$-carbon 
C)  tetrahedral geometry at the $\alpha$-carbon 
D)  double bonds within the ring 
A)  planar 
B)  positively charged at the $\alpha$-carbon 
C)  tetrahedral geometry at the $\alpha$-carbon 
D)  double bonds within the ring

Question 5

Procathepsin B is a lysosomal protease that is first translated as a proenzyme. On autocleavage it is fully activated. Procathepsin B is

Accepted Answer

A)  a zymogen. 
B)  in the T state after autocleavage. 
C)  an allosteric enzyme. 
D)  inactive at low pH. 
A)  a zymogen. 
B)  in the T state after autocleavage. 
C)  an allosteric enzyme. 
D)  inactive at low pH.

Question 6

Reaction coordinate diagrams clearly show that the energy of an enzyme bound to a transition state is higher than the energies of the E + S, E + P, and ES that occur along the same reaction coordinate. The energy of an enzyme bound to a transition state analog would lie in the diagram.

Accepted Answer

A)  above the E + S but below the transition state 
B)  below the E + S 
C)  above the transition state 
D)  above E + S but below ES 
A)  above the E + S but below the transition state 
B)  below the E + S 
C)  above the transition state 
D)  above E + S but below ES

Question 7

The hemithioacetal intermediate formed during the action of HMG-CoA reductase is stabilized by

Accepted Answer

A)  Lys267. 
B)  Asp283. 
C)  His381. 
D)  Glu83. 
A)  Lys267. 
B)  Asp283. 
C)  His381. 
D)  Glu83.

Question 8

Which pair correctly matches the coenzymes most often used to mediate the described redox reactions?

Accepted Answer

A)  NAD+/NADH; redox at C-O bonds 
B)  NADP+/NADPH; redox at C-C bonds 
C)  FAD/FADH2; redox at C-O bonds 
D)  FMN/FMNH2; redox at C-O bonds 
A)  NAD+/NADH; redox at C-O bonds 
B)  NADP+/NADPH; redox at C-C bonds 
C)  FAD/FADH2; redox at C-O bonds 
D)  FMN/FMNH2; redox at C-O bonds

Question 9

The Lineweaver-Burk plot shows data obtained for an enzyme in the absence and presence of a noncompetitive inhibitor. If the [I] is increased significantly in the experiment, the Vmaxapp would and the K app  would _.

Accepted Answer

A)  decrease; decrease 
B)  stay the same; decrease 
C)  decrease; stay the same 
D)  stay the same; stay the same 
A)  decrease; decrease 
B)  stay the same; decrease 
C)  decrease; stay the same 
D)  stay the same; stay the same

Question 10

Glutamine synthetase is in the R state when Tyr397 is

Accepted Answer

A)  deadenylated. 
B)  uridylated. 
C)  phosphorylated. 
D)  dephosphorylated. 
A)  deadenylated. 
B)  uridylated. 
C)  phosphorylated. 
D)  dephosphorylated.

Question 11

Consider the reaction coordinate diagram shown below for the conversion of substrate (S) to product (P) via two different reaction pathways that involve different transition states
(‡ and ‡*). Assume that one pathway involves a catalyst and one does not. Decide which pathway involves the catalyst and explain your logic.

Accepted Answer

The pathway containing the ‡* transition

Question 12

The glutamate side chain in the active site of HMG-CoA reductase acts as a general base only after

Accepted Answer

A)  the mevalonate binds to the active site. 
B)  the hydride from the second NADPH attacks the carbonyl center of the aldehyde. 
C)  a conformational change triggers the exchange of NADP+ for NADPH. 
D)  CoA is reduced to CoA-SH. 
A)  the mevalonate binds to the active site. 
B)  the hydride from the second NADPH attacks the carbonyl center of the aldehyde. 
C)  a conformational change triggers the exchange of NADP+ for NADPH. 
D)  CoA is reduced to CoA-SH.

Question 13

Enzymes from four different species catalyze the same reaction. Based on the reaction coordinate diagrams below, which species contains an enzyme that experiences more bonding interactions with the transition state of the reaction?

Accepted Answer

A)  species A 
B)  species B 
C)  species C 
D)  species D 
A)  species A 
B)  species B 
C)  species C 
D)  species D

Question 14

The activity of an enzyme is monitored as a function of temperature. At low temperature very little activity is seen; the activity peaks as the temperature increases and then dramatically decreases to zero as higher temperatures are attained. Explain why the activity drops off completely at higher temperatures.

Accepted Answer

The higher temperature destabi

Question 15

Given the following parameters, calculate Km.

Accepted Answer

Question 16

The role of Glu211 in the mechanism of enolase is to

Accepted Answer

A)  facilitate the orientation of the phosphate group of the substrate. 
B)  act as a general base on the substrate. 
C)  act as a general acid on the intermediate. 
D)  make the proton at the C-2 position more acidic. 
A)  facilitate the orientation of the phosphate group of the substrate. 
B)  act as a general base on the substrate. 
C)  act as a general acid on the intermediate. 
D)  make the proton at the C-2 position more acidic.

Question 17

Which of the following is NOT a function of the Mg2+ ions in the mechanism of enolase?

Accepted Answer

A)  orientation of substrate in the active site 
B)  stabilizing the intermediate 
C)  making the proton at the C-2 position more acidic 
D)  electrophilic attack on the scissile bond 
A)  orientation of substrate in the active site 
B)  stabilizing the intermediate 
C)  making the proton at the C-2 position more acidic 
D)  electrophilic attack on the scissile bond

Question 18

The three general categories of enzyme-mediated reactions, which are determined on the basis of the work they accomplish, include all EXCEPT

Accepted Answer

A)  coenzyme-dependent redox reactions. 
B)  reversible covalent modification. 
C)  hydrophobic collapse reactions. 
D)  metabolite transformation reactions. 
A)  coenzyme-dependent redox reactions. 
B)  reversible covalent modification. 
C)  hydrophobic collapse reactions. 
D)  metabolite transformation reactions.

Question 19

For a reaction of Q + R $\rightarrow$ P, the rate constant

Accepted Answer

A)  is equal to [Q][R] / [P]. 
B)  has units of s - 1. 
C)  is a second-order rate constant. 
D)  is equal to [P] / [Q][R]. 
A)  is equal to [Q][R] / [P]. 
B)  has units of s - 1. 
C)  is a second-order rate constant. 
D)  is equal to [P] / [Q][R].

Question 20

Given the following data for lactate dehydrogenase, calculate the specificity constant.

Accepted Answer

The specificity cons

Exam 7: Enzyme Mechanisms

Enzyme active sites

In vivo arginine decarboxylase activity is monitored over several days in the absence and presence of protease inhibitors. The activity is greatly reduced when protease inhibitors are present. Arginine decarboxylase is not a protease. Interpret these findings.

If the rate constant for a reaction is determined to be equal to v / [Q][R], the reaction is the conversion of

The conversion of L-proline to D-proline is shown below. Which of the following characteristics would most likely be found in a transition state analog that inhibits an enzyme that catalyzes the reaction?

Procathepsin B is a lysosomal protease that is first translated as a proenzyme. On autocleavage it is fully activated. Procathepsin B is

Reaction coordinate diagrams clearly show that the energy of an enzyme bound to a transition state is higher than the energies of the E + S, E + P, and ES that occur along the same reaction coordinate. The energy of an enzyme bound to a transition state analog would lie in the diagram.

The hemithioacetal intermediate formed during the action of HMG-CoA reductase is stabilized by

Which pair correctly matches the coenzymes most often used to mediate the described redox reactions?

The Lineweaver-Burk plot shows data obtained for an enzyme in the absence and presence of a noncompetitive inhibitor. If the [I] is increased significantly in the experiment, the Vmaxapp would and the K app would _.

Glutamine synthetase is in the R state when Tyr397 is

The glutamate side chain in the active site of HMG-CoA reductase acts as a general base only after

Enzymes from four different species catalyze the same reaction. Based on the reaction coordinate diagrams below, which species contains an enzyme that experiences more bonding interactions with the transition state of the reaction?

Given the following parameters, calculate Km.

The role of Glu211 in the mechanism of enolase is to

Which of the following is NOT a function of the Mg2+ ions in the mechanism of enolase?

The three general categories of enzyme-mediated reactions, which are determined on the basis of the work they accomplish, include all EXCEPT

For a reaction of Q + R →\rightarrow→ P, the rate constant

Given the following data for lactate dehydrogenase, calculate the specificity constant.

Principles of Biochemistry

Physical Biochemistry: Energy Conversion, Water, and Membranes

Nucleic Acid Structure and Function

Protein Structure

Methods in Protein Biochemistry

Protein Function

Cell Signaling Systems

Glycolysis: a Paradigm of Metabolic Regulation

The Citrate Cycle

Oxidative Phosphorylation

Photosynthesis

Carbohydrate Structure and Function

Carbohydrate Metabolism

Lipid Structure and Function

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Metabolic Integration

DNA Replication, Repair, and Recombination

RNA Synthesis, Processing, and Gene Silencing

Protein Synthesis, Posttranslational Modification, and Transport

Gene Regulation

Filters

The Lineweaver-Burk plot shows data obtained for an enzyme in the absence and presence of a noncompetitive inhibitor. If the [I] is increased significantly in the experiment, the V_max^app would and the K ^appwould _.

Given the following parameters, calculate K_m.

Which of the following is NOT a function of the Mg²⁺ions in the mechanism of enolase?

For a reaction of Q + R $\rightarrow$ P, the rate constant