Question 1

Most Km values of enzymes for their substrates are on the order of ________ M.

Accepted Answer

A) 10-2 
B) 10-3 
C) 10-4 
D) 10-5 
E) 10-6 
A) 10-2 
B) 10-3 
C) 10-4 
D) 10-5 
E) 10-6

Question 2

Intermediates are more stable and have longer lifetimes than transition states.

Accepted Answer

A) True 
 B)False

Question 3

The role of serine at the active site of serine proteases is to act as a(n)________ catalyst,while the histidine residue serves as a(n)________ catalyst.

Accepted Answer

A) strong;weak 
B) weak;strong 
C) acid-base;covalent 
D) covalent;acid-base 
E) anionic;ionic 
A) strong;weak 
B) weak;strong 
C) acid-base;covalent 
D) covalent;acid-base 
E) anionic;ionic

Question 4

The induced fit model of enzyme activation includes

Accepted Answer

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

Question 5

Which will be different for a catalyzed reaction versus an uncatalyzed reaction?

Accepted Answer

A) Activation energy. 
B) Ground state energy. 
C) Free energy change. 
D) All of the above. 
A) Activation energy. 
B) Ground state energy. 
C) Free energy change. 
D) All of the above.

Question 6

The catalytic triad of chymotrypsin and other serine proteases consists of

Accepted Answer

A) three subunits of the enzyme. 
B) three amino acid residues adjacent in the primary structure which act to make serine a strong nucleophile. 
C) three amino acid residues close enough in space to make serine a strong nucleophile. 
D) three enzymes with very similar structural features. 
E) None of the above. 
A) three subunits of the enzyme. 
B) three amino acid residues adjacent in the primary structure which act to make serine a strong nucleophile. 
C) three amino acid residues close enough in space to make serine a strong nucleophile. 
D) three enzymes with very similar structural features. 
E) None of the above.

Question 7

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 8

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 9

The reaction catalyzed by a certain phosphatase enzyme is found to follow ping-pong kinetics and involves the transfer of a phosphate group from substrate A to substrate B.Which mode of catalysis is likely for this reaction?

Accepted Answer

A) Sequential catalysis. 
B) Acid-base catalysis. 
C) Transfer catalysis. 
D) Covalent catalysis. 
A) Sequential catalysis. 
B) Acid-base catalysis. 
C) Transfer catalysis. 
D) Covalent catalysis.

Question 10

Transitions states bind to their enzymes more tightly than their substrates do.

Accepted Answer

A) True 
 B)False

Question 11

What shape would a graph of reaction velocity versus pH have for an enzyme that uses both a proton donor and a proton acceptor during catalysis (both acid and base catalysis)?

Accepted Answer

A) Sigmoidal. 
B) Hyperbolic. 
C) Exponential. 
D) Bell-shaped. 
E) Linear. 
A) Sigmoidal. 
B) Hyperbolic. 
C) Exponential. 
D) Bell-shaped. 
E) Linear.

Question 12

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 13

Reaction intermediates are impossible to isolate experimentally.

Accepted Answer

A) True 
 B)False

Question 14

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

Accepted Answer

A) True 
 B)False

Question 15

Radicals are stable,unreactive species that have an unpaired electron.

Accepted Answer

A) True 
 B)False

Question 16

SOD (superoxide dismutase)is an enzyme that reacts faster than the rate of diffusion of the substrate to the active site due to

Accepted Answer

A) its negative charge. 
B) electrostatic effects. 
C) the deep channel in the enzyme protein. 
D) the copper atom at the active site. 
E) All of the above. 
A) its negative charge. 
B) electrostatic effects. 
C) the deep channel in the enzyme protein. 
D) the copper atom at the active site. 
E) All of the above.

Question 17

Glycoside hydrolases such as bacterial cellulase have been shown to differ in mechanisms from that of lysozyme.They

Accepted Answer

A) are alkaline catalysts. 
B) form a boat form of the sugar. 
C) form a covalent sugar-enzyme intermediate. 
D) do not distort the substrate. 
E) have no active site side chain interactions. 
A) are alkaline catalysts. 
B) form a boat form of the sugar. 
C) form a covalent sugar-enzyme intermediate. 
D) do not distort the substrate. 
E) have no active site side chain interactions.

Question 18

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

Accepted Answer

A) True 
 B)False

Question 19

An enzyme's active site contains an arginine residue and a glutamate residue with pKa's of 2.9 and 9.1,respectively.Both residues are actively involved in the catalytic mechanism and they are the only two ionizable residues in the active site.What would you expect for the optimum pH of the enzyme?

Accepted Answer

A) 4.0 
B) 6.0 
C) 8.0 
D) No pH can be determined since the information is irrelevant to the optimum pH. 
A) 4.0 
B) 6.0 
C) 8.0 
D) No pH can be determined since the information is irrelevant to the optimum pH.

Question 20

The roles of amino acid residues at the active site of enzymes can be determined by removing certain residues using the technique of

Accepted Answer

A) specific hydrolysis. 
B) covalent binding. 
C) acylation of specific residues. 
D) site-directed mutagenesis. 
E) All of the above. 
A) specific hydrolysis. 
B) covalent binding. 
C) acylation of specific residues. 
D) site-directed mutagenesis. 
E) All of the above.

Exam 6: Mechanisms of Enzymes

Most Km values of enzymes for their substrates are on the order of ________ M.

Intermediates are more stable and have longer lifetimes than transition states.

The role of serine at the active site of serine proteases is to act as a(n)________ catalyst,while the histidine residue serves as a(n)________ catalyst.

The induced fit model of enzyme activation includes

Which will be different for a catalyzed reaction versus an uncatalyzed reaction?

The catalytic triad of chymotrypsin and other serine proteases consists of

The substrate specificity of serine proteases is primarily due to

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 reaction catalyzed by a certain phosphatase enzyme is found to follow ping-pong kinetics and involves the transfer of a phosphate group from substrate A to substrate B.Which mode of catalysis is likely for this reaction?

Transitions states bind to their enzymes more tightly than their substrates do.

What shape would a graph of reaction velocity versus pH have for an enzyme that uses both a proton donor and a proton acceptor during catalysis (both acid and base catalysis)?

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

Reaction intermediates are impossible to isolate experimentally.

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

Radicals are stable,unreactive species that have an unpaired electron.

SOD (superoxide dismutase)is an enzyme that reacts faster than the rate of diffusion of the substrate to the active site due to

Glycoside hydrolases such as bacterial cellulase have been shown to differ in mechanisms from that of lysozyme.They

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

An enzyme's active site contains an arginine residue and a glutamate residue with pKa's of 2.9 and 9.1,respectively.Both residues are actively involved in the catalytic mechanism and they are the only two ionizable residues in the active site.What would you expect for the optimum pH of the enzyme?

The roles of amino acid residues at the active site of enzymes can be determined by removing certain residues using the technique 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 Atp Synthesis

Photosynthesis

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Nucleic Acids

DNA Replication, repair, and Recombination

Transcription and RNA Processing

Protein Synthesis

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The role of serine at the active site of serine proteases is to act as a(n) catalyst,while the histidine residue serves as a(n) catalyst.