Question 1

Reaction intermediates are impossible to isolate experimentally.

Accepted Answer

A) True 
 B)False

Question 2

Both trypsin and its zymogen trypsinogen have a hydrophobic substrate-binding pocket.

Accepted Answer

A) True 
 B)False

Question 3

Site directed mutagenesis is used to study enzymes by

Accepted Answer

A)  changing the location of the active site. 
B)  producing enzymes with different amino acid residues. 
C)  producing enzymes with modified R groups. 
D)  changing the pH of the environment. 
A)  changing the location of the active site. 
B)  producing enzymes with different amino acid residues. 
C)  producing enzymes with modified R groups. 
D)  changing the pH of the environment.

Question 4

Chemical modes of catalysis are more important than binding modes of catalysis in accounting for the accelerated rates of enzymatic reactions.

Accepted Answer

A) True 
 B)False

Question 5

Transition state analogs are usually more potent inhibitors of enzyme activity than substrate analogs.

Accepted Answer

A) True 
 B)False

Question 6

Unlike lysozyme, other glycoside hydrolases such as bacterial cellulase, form covalent glycosyl-enzyme intermediates.

Accepted Answer

A) True 
 B)False

Question 7

A nucleophile is an electron poor species.

Accepted Answer

A) True 
 B)False

Question 8

The following pH dependence was found for the activity of a certain enzyme-catalyzed reaction.   If it is known that the only two ionizable residues in the active site are both glutamates, which conclusion can be drawn?

Accepted Answer

A)  The glutamates have different microenvironments which cause their pKaʹs to differ. 
B)  One of the glutamates must be amidated. 
C)  Both glutamates have a pKa equal to 5.0. 
D)  Both glutamates are deprotonated during the reaction. 
A)  The glutamates have different microenvironments which cause their pKaʹs to differ. 
B)  One of the glutamates must be amidated. 
C)  Both glutamates have a pKa equal to 5.0. 
D)  Both glutamates are deprotonated during the reaction.

Question 9

On the energy diagram below, which point represents a transition state?

Accepted Answer

A)  Point 1 
B)  Point 2 
C)  Point 3 
D)  Point 4 
A)  Point 1 
B)  Point 2 
C)  Point 3 
D)  Point 4

Question 10

Superoxide dismutase and triosphosphate isomerase are two enzymes that catalyze diffusion-controlled reactions.

Accepted Answer

A) True 
 B)False

Question 11

The mechanism of action of lysozyme includes

Accepted Answer

A)  distortion of the substrate. 
B)  acid catalysis. 
C)  proximity effects. 
D)  formation of a half-chair sugar form. 
E)  All of the above 
A)  distortion of the substrate. 
B)  acid catalysis. 
C)  proximity effects. 
D)  formation of a half-chair sugar form. 
E)  All of the above

Question 12

If a plot of enzyme activity versus pH is sigmoidal then acid-base catalysis can be ruled out as a mode of catalysis.

Accepted Answer

A) True 
 B)False

Question 13

The substrate specificity of serine proteases is primarily due to

Accepted Answer

A)  a specificity pocket in the protein. 
B)  the positions of specific side chains of serine, histidine, and aspartate. 
C)  distinct backbone conformations of the individual proteins. 
D)  A and B 
E)  A, B and C 
A)  a specificity pocket in the protein. 
B)  the positions of specific side chains of serine, histidine, and aspartate. 
C)  distinct backbone conformations of the individual proteins. 
D)  A and B 
E)  A, B and C

Question 14

Enzyme-catalyzed reactions that are diffusion-controlled reactions can never proceed any faster than the rate determined by random collision rates.

Accepted Answer

A) True 
 B)False

Question 15

In the nonpolar environment of most enzyme active sites, which statement applies to charge-charge interactions between the enzyme and the substrate?

Accepted Answer

A)  They are rare due to the non-polar environment. 
B)  They are frequent, but not very strong in the nonpolar environment. 
C)  They are stronger in the nonpolar environment. 
D)  The polarity of the active site has no effect on the strength of the charge-charge interactions. 
A)  They are rare due to the non-polar environment. 
B)  They are frequent, but not very strong in the nonpolar environment. 
C)  They are stronger in the nonpolar environment. 
D)  The polarity of the active site has no effect on the strength of the charge-charge interactions.

Question 16

The graphs below all represent the same chemical reaction, but each employing a different catalyst. Which enzyme uses the most efficient mechanism of catalysis?

Accepted Answer

A)  see graph I 
B)  see graph II 
C)  see graph III 
D)  see graph IV 
A)  see graph I 
B)  see graph II 
C)  see graph III 
D)  see graph IV

Question 17

An enzyme stabilizes the transition state that is bound in the active site. What effect will this have on the energy diagram below? The diagram shown below is for the uncatalyzed reaction.

Accepted Answer

A)  Energy of point 1 is raised. 
B)  Energy of point 2 is raised. 
C)  Energy of point 2 is lowered. 
D)  Energy of point 3 is lowered. 
E)  Energy of point 4 is raised. 
A)  Energy of point 1 is raised. 
B)  Energy of point 2 is raised. 
C)  Energy of point 2 is lowered. 
D)  Energy of point 3 is lowered. 
E)  Energy of point 4 is raised.

Question 18

The role of ser-195 in chymotrypsin cleavage of a peptide bond is that of an)

Accepted Answer

A)  acid catalyst. 
B)  proximity effector. 
C)  strong nucleophile. 
D)  weak nucleophile. 
A)  acid catalyst. 
B)  proximity effector. 
C)  strong nucleophile. 
D)  weak nucleophile.

Question 19

In the modified ʺlock-and-keyʺ theory of enzyme specificity, the key is still the enzyme while the lock is still the substrate.

Accepted Answer

A) True 
 B)False

Question 20

Induced fit of enzyme activation is a result of

Accepted Answer

A)  contact binding) of substrate. 
B)  constant small and rapid motions of protein atoms. 
C)  change to an active form. 
D)  A and B 
E)  A, B, and C 
A)  contact binding) of substrate. 
B)  constant small and rapid motions of protein atoms. 
C)  change to an active form. 
D)  A and B 
E)  A, B, and C

Exam 6: Mechanisms of Enzymes

Reaction intermediates are impossible to isolate experimentally.

Both trypsin and its zymogen trypsinogen have a hydrophobic substrate-binding pocket.

Site directed mutagenesis is used to study enzymes by

Chemical modes of catalysis are more important than binding modes of catalysis in accounting for the accelerated rates of enzymatic reactions.

Transition state analogs are usually more potent inhibitors of enzyme activity than substrate analogs.

Unlike lysozyme, other glycoside hydrolases such as bacterial cellulase, form covalent glycosyl-enzyme intermediates.

A nucleophile is an electron poor species.

The following pH dependence was found for the activity of a certain enzyme-catalyzed reaction. If it is known that the only two ionizable residues in the active site are both glutamates, which conclusion can be drawn?

On the energy diagram below, which point represents a transition state?

Superoxide dismutase and triosphosphate isomerase are two enzymes that catalyze diffusion-controlled reactions.

The mechanism of action of lysozyme includes

If a plot of enzyme activity versus pH is sigmoidal then acid-base catalysis can be ruled out as a mode of catalysis.

The substrate specificity of serine proteases is primarily due to

Enzyme-catalyzed reactions that are diffusion-controlled reactions can never proceed any faster than the rate determined by random collision rates.

In the nonpolar environment of most enzyme active sites, which statement applies to charge-charge interactions between the enzyme and the substrate?

The graphs below all represent the same chemical reaction, but each employing a different catalyst. Which enzyme uses the most efficient mechanism of catalysis?

An enzyme stabilizes the transition state that is bound in the active site. What effect will this have on the energy diagram below? The diagram shown below is for the uncatalyzed reaction.

The role of ser-195 in chymotrypsin cleavage of a peptide bond is that of an)

In the modified ʺlock-and-keyʺ theory of enzyme specificity, the key is still the enzyme while the lock is still the substrate.

Induced fit of enzyme activation is a result of

Introduction to Biochemistry

Water

Amino Acids and the Primary Structures of Proteins

Proteins: Three-Dimensional Structure and Function

Properties of Enzymes

Coenzymes and Vitamins

Carbohydrates

Lipids and Membranes

Introduction to Metabolism

Glycolysis

Gluconeogenesis, the Pentose Phosphate Pathway, and Glycogen Metabolism

The Citric Acid Cycle

Electron Transport and Oxidative Phosphorylation

Photosynthesis

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Nucleic Acids

Dna Replication, Repair, and Recombination

Transcription and Rna Processing

Protein Synthesis

Recombinant Dna Technology

Filters