Question 1

In the hydrolysis of p-nitrophenylacetate by chymotrypsin all of the following are correct EXCEPT:

Accepted Answer

A)  the first product is acetic acid. 
B)  an acetyl-enzyme intermediate forms during the mechanism. 
C)  attack of a water molecule on the acyl-enzyme intermediate yields the second product. 
D)  the active site contains a serine residue, an unprotonated histidine, and an unprotonated aspartate residue at pH 7.0 prior to binding the substrate. 
E)  none of the above. 
A)  the first product is acetic acid. 
B)  an acetyl-enzyme intermediate forms during the mechanism. 
C)  attack of a water molecule on the acyl-enzyme intermediate yields the second product. 
D)  the active site contains a serine residue, an unprotonated histidine, and an unprotonated aspartate residue at pH 7.0 prior to binding the substrate. 
E)  none of the above. A

Question 2

The transition state has an estimated life-time of about:

Accepted Answer

A)  microseconds (10−6 s). 
B)  nanoseconds (10−9 s). 
C)  (10−2 s). 
D)  (10−14 to 10−13 s). 
E)  milliseconds (10−3 s). 
A)  microseconds (10−6 s). 
B)  nanoseconds (10−9 s). 
C)  (10−2 s). 
D)  (10−14 to 10−13 s). 
E)  milliseconds (10−3 s). D

Question 3

Most covalent catalysis is carried out by enzymes using a:

Accepted Answer

A)  ping-pong kinetic mechanism. 
B)  sequential bisubstrate kinetic mechanism. 
C)  random bisubstrate kinetic mechanism. 
D)  simple unimolecular kinetic mechanism. 
E)  none of the above. 
A)  ping-pong kinetic mechanism. 
B)  sequential bisubstrate kinetic mechanism. 
C)  random bisubstrate kinetic mechanism. 
D)  simple unimolecular kinetic mechanism. 
E)  none of the above. A

Question 4

Explain transition-state analogs with an example.​

Accepted Answer

The nature of the transition state can b

Question 5

Discuss the structure of chymotrypsin.​

Accepted Answer

Chymotrypsin cleaves peptides on the car

Question 6

Because the enzymatic reaction rate is determined by the difference in energy between ES and ____, the tighter binding of the substrate, the ____ the rate of reaction.

Accepted Answer

A)  S; higher 
B)  P; lower 
C)  EX
  ; lower 
D)  EX
  ; higher 
E)  S; lower 
A)  S; higher 
B)  P; lower 
C)  EX
  ; lower 
D)  EX
  ; higher 
E)  S; lower

Question 7

Because the pKa is near 7, ____ side-chains are often involved in general acid-base catalysis.

Accepted Answer

A)  cysteine 
B)  aspartate 
C)  glutamate 
D)  lysine 
E)  histidine 
A)  cysteine 
B)  aspartate 
C)  glutamate 
D)  lysine 
E)  histidine

Question 8

Which of the following statements regarding enzymes is true?

Accepted Answer

A)  stabilization of the transition state must be less than stabilization of ES for catalysis to occur 
B)  an enzyme mechanism is vastly different from the uncatalyzed reaction 
C)  binding of substrate to an enzyme often causes strain, thus promoting transition state formation 
D)  a random single displacement mechanisms requires that substrates bind to the enzyme in a specific order 
E)  none of the above 
A)  stabilization of the transition state must be less than stabilization of ES for catalysis to occur 
B)  an enzyme mechanism is vastly different from the uncatalyzed reaction 
C)  binding of substrate to an enzyme often causes strain, thus promoting transition state formation 
D)  a random single displacement mechanisms requires that substrates bind to the enzyme in a specific order 
E)  none of the above

Question 9

Discuss the chorismate mutase active site.​

Accepted Answer

The chorismate mutase enzyme is a dimer

Question 10

Which of the following amino acids would NOT provide a nucleophilic center for covalent catalysis?

Accepted Answer

A)  alanine 
B)  lysine 
C)  glutamic acid 
D)  serine 
E)  cysteine 
A)  alanine 
B)  lysine 
C)  glutamic acid 
D)  serine 
E)  cysteine

Question 11

Discuss metal ion catalysis.​

Accepted Answer

If an enzyme binds a metal ion very tigh

Question 12

Discuss the forces involved in the destabilization of the enzyme-substrate (ES) complex.​

Accepted Answer

Destabilization of the ES complex can in

Question 13

All are true for the enzyme-transition state complex EXCEPT:

Accepted Answer

A)  It is designated as EX
  . 
B)  The enzyme stabilizes the transition-state complex more than it stabilizes the substrate complex. 
C)  The enzyme is "designed" to bind the transition-state structure more tightly than the substrate or product. 
D)  The energy barrier between ES and EX
  is less than the energy barrier between S and X
  . 
E)  All are true. 
A)  It is designated as EX
  . 
B)  The enzyme stabilizes the transition-state complex more than it stabilizes the substrate complex. 
C)  The enzyme is "designed" to bind the transition-state structure more tightly than the substrate or product. 
D)  The energy barrier between ES and EX
  is less than the energy barrier between S and X
  . 
E)  All are true.

Question 14

Which of the following are relevant to the reaction catalyzed by chorismate mutase?

Accepted Answer

A)  the reaction involves a concerted intramolecular rearrangement of chorismate to prephenate during the synthesis of phenylalanine. 
B)  the enzyme catalyzed and uncatalyzed reactions follow almost identical routes 
C)  the enzymatic reaction is thought to involve transition state stabilization by 12 electrostatic and hydrogen bond interactions 
D)  the geometry of the enzyme active site is such that the difference in energy between ES and the near attack conformation is less than 1 kJ/mol 
E)  all of the above are true 
A)  the reaction involves a concerted intramolecular rearrangement of chorismate to prephenate during the synthesis of phenylalanine. 
B)  the enzyme catalyzed and uncatalyzed reactions follow almost identical routes 
C)  the enzymatic reaction is thought to involve transition state stabilization by 12 electrostatic and hydrogen bond interactions 
D)  the geometry of the enzyme active site is such that the difference in energy between ES and the near attack conformation is less than 1 kJ/mol 
E)  all of the above are true

Question 15

The good transition state analog is one which would serve also as an extremely effective:

Accepted Answer

A)  competitive inhibitor. 
B)  noncompetitive inhibitor. 
C)  allosteric inhibitor. 
D)  mixed-noncompetitive inhibitor. 
E)  irreversible inhibitor. 
A)  competitive inhibitor. 
B)  noncompetitive inhibitor. 
C)  allosteric inhibitor. 
D)  mixed-noncompetitive inhibitor. 
E)  irreversible inhibitor.

Question 16

The mechanism of chymotrypsin involves which of the following elements?

Accepted Answer

A)  deprotonation of an active site Asp residue by His to start the reaction 
B)  formation of an acyl-enzyme intermediate that must be hydrolyzed to complete the reaction 
C)  stabilization of the positively charged His by a Gln residue 
D)  direct deprotonation of water by His to generate a hydroxide ion for initiation of the reaction 
E)  both a and b occur 
A)  deprotonation of an active site Asp residue by His to start the reaction 
B)  formation of an acyl-enzyme intermediate that must be hydrolyzed to complete the reaction 
C)  stabilization of the positively charged His by a Gln residue 
D)  direct deprotonation of water by His to generate a hydroxide ion for initiation of the reaction 
E)  both a and b occur

Question 17

If the substrate for an enzyme catalyzed reaction contained a negative charge, which of the following amino acids would most likely be present in the active site to provide electrostatic destabilization of the ES complex?

Accepted Answer

A)  Val 
B)  Asp 
C)  Arg 
D)  Ser 
E)  Gln 
A)  Val 
B)  Asp 
C)  Arg 
D)  Ser 
E)  Gln

Question 18

The initial bond formation in the covalent intermediate in the chymotrypsin catalyzed reaction is between:

Accepted Answer

A)  serine and the carbonyl carbon in the peptide backbone. 
B)  serine and the nitrogen in the peptide backbone. 
C)  histidine and the carbonyl carbon in the peptide backbone. 
D)  histidine and the nitrogen in the peptide backbone. 
E)  aspartate and the carbonyl carbon in the peptide backbone. 
A)  serine and the carbonyl carbon in the peptide backbone. 
B)  serine and the nitrogen in the peptide backbone. 
C)  histidine and the carbonyl carbon in the peptide backbone. 
D)  histidine and the nitrogen in the peptide backbone. 
E)  aspartate and the carbonyl carbon in the peptide backbone.

Question 19

Transition-state analogs are:

Accepted Answer

A)  approximations of the transition state that bind more tightly than the substrate. 
B)  compounds that compete for the active site, but are not necessarily very similar to the substrate. 
C)  stable molecules that can not be expected to resemble the true transition state too closely. 
D)  stable chemically and structurally similar molecules to the transition state. 
E)  all of the above. 
A)  approximations of the transition state that bind more tightly than the substrate. 
B)  compounds that compete for the active site, but are not necessarily very similar to the substrate. 
C)  stable molecules that can not be expected to resemble the true transition state too closely. 
D)  stable chemically and structurally similar molecules to the transition state. 
E)  all of the above.

Question 20

In the catalytic triad common to many serine proteases, _____ increases the basicity of _____, thus allowing deprotonation of _____ to serve as a nucleophile.

Accepted Answer

A)  Ser-His-Asp 
B)  His-Ser-Asp 
C)  Ser-His-His 
D)  Asp-His-Ser 
E)  Cys-His-Ser 
A)  Ser-His-Asp 
B)  His-Ser-Asp 
C)  Ser-His-His 
D)  Asp-His-Ser 
E)  Cys-His-Ser

Exam 14: Mechanisms of Enzyme Action

In the hydrolysis of p-nitrophenylacetate by chymotrypsin all of the following are correct EXCEPT:

The transition state has an estimated life-time of about:

Most covalent catalysis is carried out by enzymes using a:

Explain transition-state analogs with an example.​

Discuss the structure of chymotrypsin.​

Because the enzymatic reaction rate is determined by the difference in energy between ES and ____, the tighter binding of the substrate, the ____ the rate of reaction.

Because the pKa is near 7, ____ side-chains are often involved in general acid-base catalysis.

Which of the following statements regarding enzymes is true?

Discuss the chorismate mutase active site.​

Which of the following amino acids would NOT provide a nucleophilic center for covalent catalysis?

Discuss metal ion catalysis.​

Discuss the forces involved in the destabilization of the enzyme-substrate (ES) complex.​

All are true for the enzyme-transition state complex EXCEPT:

Which of the following are relevant to the reaction catalyzed by chorismate mutase?

The good transition state analog is one which would serve also as an extremely effective:

The mechanism of chymotrypsin involves which of the following elements?

If the substrate for an enzyme catalyzed reaction contained a negative charge, which of the following amino acids would most likely be present in the active site to provide electrostatic destabilization of the ES complex?

The initial bond formation in the covalent intermediate in the chymotrypsin catalyzed reaction is between:

Transition-state analogs are:

In the catalytic triad common to many serine proteases, _____ increases the basicity of _____, thus allowing deprotonation of _____ to serve as a nucleophile.

The Facts of Life: Chemistry Is the Logic of Biological Phenomena

Water: the Medium of Life

Thermodynamics of Biological Systems

Amino Acids and the Peptide Bond

Proteins: Their Primary Structure and Biological Functions

Proteins: Secondary, Tertiary, and Quaternary Structure

Carbohydrates and the Glycoconjugates of Cell Surfaces

Lipids

Membranes and Membrane Transport

Nucleotides and Nucleic Acids

Structure of Nucleic Acids

Recombinant Dna, Cloning, Chimeric Genes, and Synthetic Biology

Enzymeskinetics and Specificity

Enzyme Regulation

Molecular Motors

Metabolism: an Overview

Glycolysis

The Tricarboxylic Acid Cycle

Electron Transport and Oxidative Phosphorylation

Photosynthesis

Gluconeogenesis, Glycogen Metabolism, and the Pentose Phosphate Pathway

Fatty Acid Catabolism

Lipid Biosynthesis

Nitrogen Acquisition and Amino Acid Metabolism

Synthesis and Degradation of Nucleotides

Metabolic Integration and Organ Specialization

Dna Metabolism: Replication, Recombination, and Repair

Transcription and the Regulation of Gene Expression

Protein Synthesis

Completing the Protein Life Cycle: Folding, Processing, and Degradation

The Reception and Transmission of Extracellular Information

Filters

Explain transition-state analogs with an example.

Discuss the structure of chymotrypsin.

Because the enzymatic reaction rate is determined by the difference in energy between ES and , the tighter binding of the substrate, the the rate of reaction.

Because the pK_a is near 7, ____ side-chains are often involved in general acid-base catalysis.

Discuss the chorismate mutase active site.

Discuss metal ion catalysis.

Discuss the forces involved in the destabilization of the enzyme-substrate (ES) complex.

In the catalytic triad common to many serine proteases, ___ increases the basicity of _, thus allowing deprotonation of ___ to serve as a nucleophile.