Question 1

A reaction that occurs with every collision between reactant molecules is called a(n)________.

Accepted Answer

A) saturation point 
B) diffusion-controlled reaction 
C) rate-determining step 
D) first order reaction 
A) saturation point 
B) diffusion-controlled reaction 
C) rate-determining step 
D) first order reaction B

Question 2

Experiments on the bacterial serine protease subtilisin show that even when all three residues of the catalytic triad are mutated,the catalytic rate of the enzyme is still 3000 times the uncatalyzed reaction rate.Which mode of catalysis is likely responsible for this remaining catalytic activity?

Accepted Answer

A) Acid-base catalysis. 
B) Covalent catalysis. 
C) Transition-state stabilization. 
D) Hydrophobic effects. 
A) Acid-base catalysis. 
B) Covalent catalysis. 
C) Transition-state stabilization. 
D) Hydrophobic effects. C

Question 3

A nucleophile is an electron poor species.

Accepted Answer

A) True 
 B)False  False

Question 4

Aspartate and lysine are in the active site of an enzyme.They are both known to participate directly in catalysis.The pKa's of the residues are found to be 3.2 and 9.6,respectively for aspartate and lysine.The optimum pH for the enzyme is 6.4.Which forms of these two residues will predominate when the enzyme is most active?

Accepted Answer

A) Aspartate is protonated;lysine is deprotonated. 
B) Both residues are protonated. 
C) Aspartate is deprotonated;lysine is protonated. 
D) Both residues are deprotonated. 
A) Aspartate is protonated;lysine is deprotonated. 
B) Both residues are protonated. 
C) Aspartate is deprotonated;lysine is protonated. 
D) Both residues are deprotonated.

Question 5

Lysozyme is classified as a

Accepted Answer

A) Phosphorylase. 
B) Oxidoreductase. 
C) Isomerase. 
D) Transferase. 
E) Hydrolase. 
A) Phosphorylase. 
B) Oxidoreductase. 
C) Isomerase. 
D) Transferase. 
E) Hydrolase.

Question 6

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

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 7

Trypsin as well as chymotrypsin can activate chymotrypsinogen to chymotrypsin.

Accepted Answer

A) True 
 B)False

Question 8

Histidine is an ideal amino acid at neutral pH values at the active site of many enzymes because

Accepted Answer

A) it is hydrophobic. 
B) it engages in electron transfer. 
C) it is not ionizable. 
D) its R group has a pKa of about 6 to 7 in most proteins. 
A) it is hydrophobic. 
B) it engages in electron transfer. 
C) it is not ionizable. 
D) its R group has a pKa of about 6 to 7 in most proteins.

Question 9

When the concentration of a substrate inside a cell falls below the substrate concentration at half maximal velocity,________.

Accepted Answer

A) ES is formed more easily 
B) ES dissociates to E + S 
C) ES is closer to the ground state than to the transition state 
D) E + S is in equilibrium with ES 
E) the reaction will not proceed 
A) ES is formed more easily 
B) ES dissociates to E + S 
C) ES is closer to the ground state than to the transition state 
D) E + S is in equilibrium with ES 
E) the reaction will not proceed

Question 10

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 11

The proximity effect of speeding an enzyme-catalyzed reaction is explained by ________.

Accepted Answer

A) a large loss of entropy when reactive groups are brought close to each other 
B) a large gain in entropy due to binding of the substrate 
C) a conversion of a reaction from endergonic to exergonic 
D) increasing the flexibility of the substrate by increasing its degrees of freedom of rotation 
A) a large loss of entropy when reactive groups are brought close to each other 
B) a large gain in entropy due to binding of the substrate 
C) a conversion of a reaction from endergonic to exergonic 
D) increasing the flexibility of the substrate by increasing its degrees of freedom of rotation

Question 12

X-ray crystallographic examination of the active site of arginine kinase was possible because

Accepted Answer

A) it could be crystallized in the different structural forms. 
B) nitrate could be substituted for phosphate in the reaction. 
C) it was readily purified (unlike most other enzymes). 
D) MgADP was involved in the reaction. 
E) All of the above. 
A) it could be crystallized in the different structural forms. 
B) nitrate could be substituted for phosphate in the reaction. 
C) it was readily purified (unlike most other enzymes). 
D) MgADP was involved in the reaction. 
E) All of the above.

Question 13

Enzymes which have induced fit to the substrate are generally more effective than those in an active form initially.

Accepted Answer

A) True 
 B)False

Question 14

In the reaction below,Y- is ________. Y- + CH₂X → CH₂Y + X-

Accepted Answer

A) the leaving group 
B) the attacking electrophile 
C) the reaction intermediate 
D) a nucleophile 
A) the leaving group 
B) the attacking electrophile 
C) the reaction intermediate 
D) a nucleophile

Question 15

In the Ser-His-Asp catalytic triad in serine proteases,the serine residue serves as an acid-base catalyst,while the histidine residue serves as a covalent catalyst.

Accepted Answer

A) True 
 B)False

Question 16

Which represents a hydride ion?

Accepted Answer

A) H₂- 
B) H- 
C) H+ 
D) H₃O+ 
A) H₂- 
B) H- 
C) H+ 
D) H₃O+

Question 17

In the following chemical reaction which species is the reducing agent? 
CH₄ + 2 O2 → CO2 + 2 H₂O

Accepted Answer

A) CH₄ 
B) O2 
C) CO2 
D) H₂O 
E) None of the above,this is not an oxidation-reduction reaction. 
A) CH₄ 
B) O2 
C) CO2 
D) H₂O 
E) None of the above,this is not an oxidation-reduction reaction.

Question 18

Weak substrate binding is an important feature to help describe enzyme catalysis.

Accepted Answer

A) True 
 B)False

Question 19

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

Accepted Answer

A) True 
 B)False

Question 20

Replacement of the amino acid ________ at or near an active site of an enzyme is more likely to change enzyme activity than the replacement of ________ at or near the active site.

Accepted Answer

A) histidine;leucine 
B) leucine;histidine 
C) leucine;isoleucine 
D) histidine;aspartate 
A) histidine;leucine 
B) leucine;histidine 
C) leucine;isoleucine 
D) histidine;aspartate

Exam 6: Mechanisms of Enzymes

A reaction that occurs with every collision between reactant molecules is called a(n)________.

Experiments on the bacterial serine protease subtilisin show that even when all three residues of the catalytic triad are mutated,the catalytic rate of the enzyme is still 3000 times the uncatalyzed reaction rate.Which mode of catalysis is likely responsible for this remaining catalytic activity?

A nucleophile is an electron poor species.

Lysozyme is classified as a

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

Trypsin as well as chymotrypsin can activate chymotrypsinogen to chymotrypsin.

Histidine is an ideal amino acid at neutral pH values at the active site of many enzymes because

When the concentration of a substrate inside a cell falls below the substrate concentration at half maximal velocity,________.

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

The proximity effect of speeding an enzyme-catalyzed reaction is explained by ________.

X-ray crystallographic examination of the active site of arginine kinase was possible because

Enzymes which have induced fit to the substrate are generally more effective than those in an active form initially.

In the reaction below,Y- is ________. Y- + CH₂X → CH₂Y + X-

In the Ser-His-Asp catalytic triad in serine proteases,the serine residue serves as an acid-base catalyst,while the histidine residue serves as a covalent catalyst.

Which represents a hydride ion?

In the following chemical reaction which species is the reducing agent? CH₄ + 2 O2 → CO2 + 2 H₂O

Weak substrate binding is an important feature to help describe enzyme catalysis.

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

Replacement of the amino acid ________ at or near an active site of an enzyme is more likely to change enzyme activity than the replacement of ________ at or near the active site.

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

Filters

In the following chemical reaction which species is the reducing agent? CH₄ + 2 O₂ → CO₂ + 2 H₂O

Replacement of the amino acid at or near an active site of an enzyme is more likely to change enzyme activity than the replacement of at or near the active site.