Question 1

Enzymes that bind reaction transition states with greater affinity than substrates or products

Accepted Answer

A) have a lower free energy ES complex than E + S. 
B) increase reaction rates by decreasing the concentration of the transition state . 
C) progress slowly due to the stability of the transition state complex. 
D) compensate for small differences in the energy of the free substrate and free product. 
E) All of the above are correct. 
A) have a lower free energy ES complex than E + S. 
B) increase reaction rates by decreasing the concentration of the transition state . 
C) progress slowly due to the stability of the transition state complex. 
D) compensate for small differences in the energy of the free substrate and free product. 
E) All of the above are correct.

Question 2

If you add enzyme to a solution containing only the product(s)of a reaction, would you expect any substrate to form?

Accepted Answer

A) It depends on the time interval and temperature of reaction. 
B) It depends on the concentration of products added. 
C) It depends on the energy difference between E + P and the transition state. 
D) All of the above may determine if product forms. 
E) None of the above determines if product forms. 
A) It depends on the time interval and temperature of reaction. 
B) It depends on the concentration of products added. 
C) It depends on the energy difference between E + P and the transition state. 
D) All of the above may determine if product forms. 
E) None of the above determines if product forms.

Question 3

______ metals are the most common metallic enzyme cofactors.

Accepted Answer

A) Actinide 
B) Alkali 
C) Heavy 
D) Rare earth 
E) Transition 
A) Actinide 
B) Alkali 
C) Heavy 
D) Rare earth 
E) Transition

Question 4

A new serine protease was discovered that preferentially cleaves a peptide bond adjoining a negatively charged side chain.Which of the following is true?

Accepted Answer

A) The specificity pocket would mimic that of chymotrypsin. 
B) The specificity pocket would mimic that of trypsin. 
C) The specificity pocket is likely lined with amino acids such as Arg and Lys. 
D) It likely reacts much slower than chymotrypsin. 
E) It likely reaction much faster than chymotrypsin. 
A) The specificity pocket would mimic that of chymotrypsin. 
B) The specificity pocket would mimic that of trypsin. 
C) The specificity pocket is likely lined with amino acids such as Arg and Lys. 
D) It likely reacts much slower than chymotrypsin. 
E) It likely reaction much faster than chymotrypsin.

Question 5

Consider the Schiff base formation reaction discussed in the catalytic mechanisms section of the chapter.What would probably happen if the carboxylate group was stabilized by a nearby positive charge?

Accepted Answer

A) The Schiff base would donate a lone pair of electrons to the substrate. 
B) The Schiff base would form prior to decarboxylation. 
C) The reaction would proceed with nucleophilic attack on the enzyme by the electrophilic substrate. 
D) All of the above would be possible given the discussed mechanism with a stabilized carboxyl group. 
E) None of the above is plausible considering the discussed mechanism with a stabilized carboxylate group. 
A) The Schiff base would donate a lone pair of electrons to the substrate. 
B) The Schiff base would form prior to decarboxylation. 
C) The reaction would proceed with nucleophilic attack on the enzyme by the electrophilic substrate. 
D) All of the above would be possible given the discussed mechanism with a stabilized carboxyl group. 
E) None of the above is plausible considering the discussed mechanism with a stabilized carboxylate group.

Question 6

In affinity labeling, a technique used to study enzyme mechanisms,

Accepted Answer

A) A compound designed to bind at the active site reacts with and therefore permits the identification of a nearby group. 
B) A fluorescent group is attached to the substrate to identify the position of the active site. 
C) Highly purified enzyme is obtained by affinity chromatography for mechanistic studies. 
D) A radioactive isotope is incorporated into the substrate to identify the position of the active site. 
E) Genetic modification of amino acid residues is used to alter the binding affinity of the active site. 
A) A compound designed to bind at the active site reacts with and therefore permits the identification of a nearby group. 
B) A fluorescent group is attached to the substrate to identify the position of the active site. 
C) Highly purified enzyme is obtained by affinity chromatography for mechanistic studies. 
D) A radioactive isotope is incorporated into the substrate to identify the position of the active site. 
E) Genetic modification of amino acid residues is used to alter the binding affinity of the active site.

Question 7

Which of the following processes would yield and increase in rate?

Accepted Answer

A) the proximity of the reacting groups 
B) the rotational motions of the substrates and catalytic groups 
C) the orientations of the substrates and catalytic groups 
D) all of the above 
E) none of the above 
A) the proximity of the reacting groups 
B) the rotational motions of the substrates and catalytic groups 
C) the orientations of the substrates and catalytic groups 
D) all of the above 
E) none of the above

Question 8

An uncatalyzed reaction has a rate of 4.2 × 10-7 sec-1.When an enzyme is added the rate is 3.2 × 104 sec-1.Calculate the rate enhancement caused by the enzyme.

Accepted Answer

A) 3.2 × 104 
B) 7.4 × 10-3 
C) 1.3 × 10-2 
D) 7.6 × 1010 
E) The data are not appropriate for the calculation requested. 
A) 3.2 × 104 
B) 7.4 × 10-3 
C) 1.3 × 10-2 
D) 7.6 × 1010 
E) The data are not appropriate for the calculation requested.

Question 9

Matching
-If an enzyme-catalyzed reaction has a low rate at low pH and high rate at higher pH, this implies that a group on either the enzyme or the substrate must be ______ for an efficient reaction.

Accepted Answer

A) high 
B) deprotonated 
C) protonated 
D) catalytic mechanism 
E) covalent
F)rate-determining step
G)leaving group
H)formation of ES
I)amino acid
J)low
K)coenzymes
L)concerted acid-base
M)orientation
N)oxidation 
A) high 
B) deprotonated 
C) protonated 
D) catalytic mechanism 
E) covalent
F)rate-determining step
G)leaving group
H)formation of ES
I)amino acid
J)low
K)coenzymes
L)concerted acid-base
M)orientation
N)oxidation

Question 10

Zymogens are not enzymatically active because

Accepted Answer

A) the active site amino acids have been mutated. 
B) they have not yet bound the proper cofactor. 
C) their environment has the wrong pH. 
D) they are not yet shaped such that essential proximity and orientation catalysis can occur. 
E) None of the above is correct. 
A) the active site amino acids have been mutated. 
B) they have not yet bound the proper cofactor. 
C) their environment has the wrong pH. 
D) they are not yet shaped such that essential proximity and orientation catalysis can occur. 
E) None of the above is correct.

Question 11

A recent discovery has suggested that a gene mutation results in several amino acid substitutions within an active site.The following substitutions have been identified and are each expected to form the active site:   It was also noticed that a coenzyme molecule containing a hydroxyl (-OH)group binds to the mutated protein in approximately the same location as the original serine but does not alter the structure of the protein in anyway.Based on your knowledge of amino acids, enzymes, and catalysis, which of the following is a REASONABLE conclusion?

Accepted Answer

A) The mutant protein cleaves on the carboxy side of phenylalanine. 
B) The mutant protein cleaves peptide bonds on the carboxy side of glutamate or aspartate. 
C) The mutant protein cleaves peptide bonds on the carboxy side of lysine or arginine. 
D) The mutant protein functions identical to chymotrypsin. 
E) The mutant protein has no function. 
A) The mutant protein cleaves on the carboxy side of phenylalanine. 
B) The mutant protein cleaves peptide bonds on the carboxy side of glutamate or aspartate. 
C) The mutant protein cleaves peptide bonds on the carboxy side of lysine or arginine. 
D) The mutant protein functions identical to chymotrypsin. 
E) The mutant protein has no function.

Question 12

Which of the following is TRUE regarding cofactors?

Accepted Answer

A) Coenzymes are often separate from the enzyme and do not need recharged. 
B) Metal ions must be covalently attached to function as a cofactor. 
C) Cofactor is a broad term used for all enzyme "helpers". 
D) Prosthetic groups can dissociate readily and be regenerated for use in another enzyme. 
E) An apoenzyme implies that a cofactor is present. 
A) Coenzymes are often separate from the enzyme and do not need recharged. 
B) Metal ions must be covalently attached to function as a cofactor. 
C) Cofactor is a broad term used for all enzyme "helpers". 
D) Prosthetic groups can dissociate readily and be regenerated for use in another enzyme. 
E) An apoenzyme implies that a cofactor is present.

Question 13

The imidazole side chain of histidine can function as either a general acid catalyst or a general base catalyst because
I.the imidazole group has a pKa in the physiological pH range.
II.in the physiological pH range, the nitrogen in the ring can be easily protonated/deprotonated.
III.one guanidino group is protonated, and the other is deprotonated at physiological pH.
IV.the imidazole group is a strong reducing agent at physiological pH.

Accepted Answer

A) I, II 
B) I 
C) II, IV 
D) II, III 
E) IV 
A) I, II 
B) I 
C) II, IV 
D) II, III 
E) IV

Question 14

Serine proteases use _________ to catalyze the cleavage of a peptide bond.
I.covalent catalysis
II.proximity and orientation effects
III.general base catalysis
IV.electrostatic catalysis

Accepted Answer

A) I, II 
B) II 
C) III 
D) I, II, III 
E) I, II, III, IV 
A) I, II 
B) II 
C) III 
D) I, II, III 
E) I, II, III, IV

Question 15

Why can histidine NOT act as a base in the lysosome (an organelle where the pH is close to 4.5)?

Accepted Answer

A) Histidine has a positive charge at pH 4.5. 
B) Histidine has a side chain pK close to 6. 
C) Histidine would be protonated at pH 4.5. 
D) All of the above are correct. 
E) None of the above is correct. 
A) Histidine has a positive charge at pH 4.5. 
B) Histidine has a side chain pK close to 6. 
C) Histidine would be protonated at pH 4.5. 
D) All of the above are correct. 
E) None of the above is correct.

Question 16

Which of these amino acid groups would not make a good nucleophilic catalyst?

Accepted Answer

A) amino 
B) sulfhydryl 
C) imidazole 
D) methyl 
E) hydroxyl 
A) amino 
B) sulfhydryl 
C) imidazole 
D) methyl 
E) hydroxyl

Question 17

Which of the following is TRUE regarding transition state?

Accepted Answer

A) The free energy between the transition state and the reactants must be negative. 
B) The transition state can be stabilized by covalent catalysis. 
C) The transition state represents the ES complex. 
D) Transition state analogs bind the substrate not the enzyme 
E) All of the above are true. 
A) The free energy between the transition state and the reactants must be negative. 
B) The transition state can be stabilized by covalent catalysis. 
C) The transition state represents the ES complex. 
D) Transition state analogs bind the substrate not the enzyme 
E) All of the above are true.

Question 18

A peptide with the sequence "Glu-Ser-Val-Asp-Lys" will likely be cut next to "Val" rapidly by _______ and very slowly by ____.
I.chymotrypsin
II.trypsin
III.trypsinogen
IV.elastase

Accepted Answer

A) I,IV 
B) I, II 
C) II, III 
D) IV, II 
E) IV, I 
A) I,IV 
B) I, II 
C) II, III 
D) IV, II 
E) IV, I

Question 19

Which of the following would result in the greatest decrease in function of the catalytic triad found in serine proteases?

Accepted Answer

A) Mutation to Ser, Cys, Asp 
B) Mutation to Ser, His, Asp 
C) Mutation to Cys, His, Asp 
D) Mutation to Ser, His, Glu 
E) Mutation to Cys, His, Glu 
A) Mutation to Ser, Cys, Asp 
B) Mutation to Ser, His, Asp 
C) Mutation to Cys, His, Asp 
D) Mutation to Ser, His, Glu 
E) Mutation to Cys, His, Glu

Question 20

Curved arrows are conventionally used to illustrate the movement of

Accepted Answer

A) electron pairs. 
B) single electrons. 
C) protons. 
D) anions. 
E) All of the above use this convention. 
A) electron pairs. 
B) single electrons. 
C) protons. 
D) anions. 
E) All of the above use this convention.

Exam 11: Enzyme Catalysis

Enzymes that bind reaction transition states with greater affinity than substrates or products

If you add enzyme to a solution containing only the product(s)of a reaction, would you expect any substrate to form?

______ metals are the most common metallic enzyme cofactors.

A new serine protease was discovered that preferentially cleaves a peptide bond adjoining a negatively charged side chain.Which of the following is true?

Consider the Schiff base formation reaction discussed in the catalytic mechanisms section of the chapter.What would probably happen if the carboxylate group was stabilized by a nearby positive charge?

In affinity labeling, a technique used to study enzyme mechanisms,

Which of the following processes would yield and increase in rate?

An uncatalyzed reaction has a rate of 4.2 × 10-7 sec-1.When an enzyme is added the rate is 3.2 × 104 sec-1.Calculate the rate enhancement caused by the enzyme.

Matching -If an enzyme-catalyzed reaction has a low rate at low pH and high rate at higher pH, this implies that a group on either the enzyme or the substrate must be ______ for an efficient reaction.

Zymogens are not enzymatically active because

Which of the following is TRUE regarding cofactors?

Serine proteases use _________ to catalyze the cleavage of a peptide bond. I.covalent catalysis II.proximity and orientation effects III.general base catalysis IV.electrostatic catalysis

Why can histidine NOT act as a base in the lysosome (an organelle where the pH is close to 4.5)?

Which of these amino acid groups would not make a good nucleophilic catalyst?

Which of the following is TRUE regarding transition state?

A peptide with the sequence "Glu-Ser-Val-Asp-Lys" will likely be cut next to "Val" rapidly by _______ and very slowly by ____. I.chymotrypsin II.trypsin III.trypsinogen IV.elastase

Which of the following would result in the greatest decrease in function of the catalytic triad found in serine proteases?

Curved arrows are conventionally used to illustrate the movement of

Introduction to the Chemistry of Life

Water

Nucleotides, Nucleic Acids, and Genetic Information

Amino Acids

Proteins: Primary Structure

Proteins: Three-Dimensional Structure

Protein Function Part I: Myoglobin and Hemoglobin

Carbohydrates

Lipids and Biological Membranes

Membrane Transport

Enzyme Kinetics, Inhibition and Control

Biochemical Signaling

Introduction to Metabolism

Glycogen Metabolism and Gluconeogenesis

Glucose Catabolism

Citric Acid Cycle

Electron Transport and Oxidative Phosphorylation

Photosynthesis

Lipid Metabolism

Amino Acid Metabolism

Mammalian Fuel Metabolism: Integration and Regulation

Nucleotide Metabolism

Nucleic Acid Structure

Dna Replication, Repair and Recombination

Transcription and Rna Processing

Translation

Regulation of Gene Expression

Filters

An uncatalyzed reaction has a rate of 4.2 × 10^-7 sec^-1.When an enzyme is added the rate is 3.2 × 10⁴ sec^-1.Calculate the rate enhancement caused by the enzyme.

A peptide with the sequence "Glu-Ser-Val-Asp-Lys" will likely be cut next to "Val" rapidly by ___ and very slowly by . I.chymotrypsin II.trypsin III.trypsinogen IV.elastase