Question 1

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. C

Question 2

A mutation of Lys229 in aldolase leads to a loss of enzyme activity.This is most likely because the

Accepted Answer

A)  active site can no longer exclude water. 
B)  active site can no longer include water. 
C)  enzyme can no longer hold the intermediate in the correct orientation for catalysis. 
D)  product will remain bound to the enzyme active site. 
A)  active site can no longer exclude water. 
B)  active site can no longer include water. 
C)  enzyme can no longer hold the intermediate in the correct orientation for catalysis. 
D)  product will remain bound to the enzyme active site. C

Question 3

Describe two conformational changes that occur when aspartate transcarbamoylase shifts from the R state to the T state.

Accepted Answer

The catalytic subunits are brought closer together.The catalytic subunits rotate.

Question 4

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 5

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 6

Refer to the reaction coordinate diagram below.At what point is there a maximum number of interactions between the enzyme and the compound that it is binding?

Accepted Answer

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

Question 7

The transition state of a reaction is

Accepted Answer

A)  higher in free energy than the product. 
B)  lower in free energy than the ground state of the substrate. 
C)  easily isolated. 
D)  equal to the  G‡ of the uncatalyzed reaction minus the  G‡ of the catalyzed reaction. 
A)  higher in free energy than the product. 
B)  lower in free energy than the ground state of the substrate. 
C)  easily isolated. 
D)  equal to the  G‡ of the uncatalyzed reaction minus the  G‡ of the catalyzed reaction.

Question 8

A mixture of enzyme and inhibitor is run through a size-exclusion chromatography column.The activity of the enzyme is assessed before and after the chromatography.The enzyme has more activity after the chromatography step.Which of the following is true?

Accepted Answer

A)  The enzyme was not eluted fully from the column. 
B)  The enzyme was denatured during chromatography. 
C)  The inhibitor is a reversible inhibitor. 
D)  The inhibitor is an irreversible inhibitor. 
A)  The enzyme was not eluted fully from the column. 
B)  The enzyme was denatured during chromatography. 
C)  The inhibitor is a reversible inhibitor. 
D)  The inhibitor is an irreversible inhibitor.

Question 9

An enzyme undergoes a mutation that causes it to lose the ability to be regulated via phosphorylation.Which of the following mutations may lead to this loss of regulation? Assume that the overall structure is not altered by the mutation.

Accepted Answer

A)  Ser  Thr 
B)  Thr  Ser 
C)  Tyr  Phe 
D)  Ser  Tyr 
A)  Ser  Thr 
B)  Thr  Ser 
C)  Tyr  Phe 
D)  Ser  Tyr

Question 10

A Lineweaver-Burk plot displays parallel lines for an enzyme in the absence and presence of increasing amounts of an inhibitor.The inhibitor in this experiment

Accepted Answer

A)  binds both the free enzyme and the ES complex. 
B)  is competitive. 
C)  alters the Km but not the vmax. 
D)  is uncompetitive. 
A)  binds both the free enzyme and the ES complex. 
B)  is competitive. 
C)  alters the Km but not the vmax. 
D)  is uncompetitive.

Question 11

A plot of v0 versus substrate concentration for aspartate transcarbamoylase displays a sigmoidal curve.Explain how the plot would change in the presence of CTP.

Accepted Answer

CTP is an allosteric inhibitor

Question 12

In the steady-state condition assumed in Michaelis-Menten kinetics,__________ is relatively constant.

Accepted Answer

A)  [ES] 
B)  [S] 
C)  v0 
D)  [ES] / [S] 
A)  [ES] 
B)  [S] 
C)  v0 
D)  [ES] / [S]

Question 13

In a reversible covalent modification reaction involving the phosphorylation of a target protein,which of the following amino acids is LEAST likely to be modified with a phosphate group?

Accepted Answer

A)  Ser 
B)  Phe 
C)  Tyr 
D)  Thr 
A)  Ser 
B)  Phe 
C)  Tyr 
D)  Thr

Question 14

The initial velocity of an enzyme-catalyzed reaction is followed at various substrate concentrations.At very high substrate concentrations it is observed that the initial velocity no longer increases as more substrate is added.The velocity under these conditions is known as

Accepted Answer

A)  the ultimate velocity. 
B)  the maximum velocity. 
C)  v[S]. 
D)  optimal velocity. 
A)  the ultimate velocity. 
B)  the maximum velocity. 
C)  v[S]. 
D)  optimal velocity.

Question 15

Place the following HMG-CoA reductase steps in the correct order: A.Reduction of aldehyde
B.Breakdown of hemithioacetal
C.Reduction of thioester
D.Cofactor exchange

Accepted Answer

A)  A, D, C, B 
B)  C, D, B, A 
C)  A, B, D, C 
D)  C, B, D, A 
A)  A, D, C, B 
B)  C, D, B, A 
C)  A, B, D, C 
D)  C, B, D, A

Question 16

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 17

Which answer correctly pairs the enzyme class with the type of reaction catalyzed?

Accepted Answer

A)  lyase; formation of two products by hydrolyzing a substrate 
B)  transferase; transfer of H or O atoms 
C)  isomerase; intramolecular rearrangements 
D)  oxidoreductase; transfer of groups within molecules 
A)  lyase; formation of two products by hydrolyzing a substrate 
B)  transferase; transfer of H or O atoms 
C)  isomerase; intramolecular rearrangements 
D)  oxidoreductase; transfer of groups within molecules

Question 18

Refer to the reaction coordinate diagram below.The change in the activation energy of the reaction because of the presence of an enzyme is illustrated by the energy of __________ minus the energy of __________.

Accepted Answer

A)  B; A 
B)  B; C 
C)  B; D 
D)  C; D 
A)  B; A 
B)  B; C 
C)  B; D 
D)  C; D

Question 19

Which of the following pairs correctly matches the type of interaction observed between an inhibitor and an enzyme with the type of inhibition?

Accepted Answer

A)  ionic; irreversible 
B)  covalent; irreversible 
C)  hydrogen bonding; reversible 
D)  hydrophobic; irreversible 
A)  ionic; irreversible 
B)  covalent; irreversible 
C)  hydrogen bonding; reversible 
D)  hydrophobic; irreversible

Question 20

Which of the following statements are true?

Accepted Answer

A)  ATCase is regulated by feedback inhibition. 
B)  CTP is an allosteric activator of ATCase. 
C)  ATP is an allosteric inhibitor of ATCase. 
D)  GTP is an allosteric inhibitor of ATCase. 
A)  ATCase is regulated by feedback inhibition. 
B)  CTP is an allosteric activator of ATCase. 
C)  ATP is an allosteric inhibitor of ATCase. 
D)  GTP is an allosteric inhibitor of ATCase.

Exam 7: Enzyme Mechanisms

The role of Glu211 in the mechanism of enolase is to

A mutation of Lys229 in aldolase leads to a loss of enzyme activity.This is most likely because the

Describe two conformational changes that occur when aspartate transcarbamoylase shifts from the R state to the T state.

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.

Refer to the reaction coordinate diagram below.At what point is there a maximum number of interactions between the enzyme and the compound that it is binding?

The transition state of a reaction is

A mixture of enzyme and inhibitor is run through a size-exclusion chromatography column.The activity of the enzyme is assessed before and after the chromatography.The enzyme has more activity after the chromatography step.Which of the following is true?

An enzyme undergoes a mutation that causes it to lose the ability to be regulated via phosphorylation.Which of the following mutations may lead to this loss of regulation? Assume that the overall structure is not altered by the mutation.

A Lineweaver-Burk plot displays parallel lines for an enzyme in the absence and presence of increasing amounts of an inhibitor.The inhibitor in this experiment

A plot of v0 versus substrate concentration for aspartate transcarbamoylase displays a sigmoidal curve.Explain how the plot would change in the presence of CTP.

In the steady-state condition assumed in Michaelis-Menten kinetics,__________ is relatively constant.

In a reversible covalent modification reaction involving the phosphorylation of a target protein,which of the following amino acids is LEAST likely to be modified with a phosphate group?

The initial velocity of an enzyme-catalyzed reaction is followed at various substrate concentrations.At very high substrate concentrations it is observed that the initial velocity no longer increases as more substrate is added.The velocity under these conditions is known as

Place the following HMG-CoA reductase steps in the correct order: A.Reduction of aldehyde B.Breakdown of hemithioacetal C.Reduction of thioester D.Cofactor exchange

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

Which answer correctly pairs the enzyme class with the type of reaction catalyzed?

Refer to the reaction coordinate diagram below.The change in the activation energy of the reaction because of the presence of an enzyme is illustrated by the energy of __________ minus the energy of __________.

Which of the following pairs correctly matches the type of interaction observed between an inhibitor and an enzyme with the type of inhibition?

Which of the following statements are true?

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

A mutation of Lys₂₂₉ in aldolase leads to a loss of enzyme activity.This is most likely because the

A plot of v₀ versus substrate concentration for aspartate transcarbamoylase displays a sigmoidal curve.Explain how the plot would change in the presence of CTP.

Refer to the reaction coordinate diagram below.The change in the activation energy of the reaction because of the presence of an enzyme is illustrated by the energy of minus the energy of .