Question 1

How is the half-reaction Cu²+ + 2e- → Cu classified?

Accepted Answer

A) Free radical reaction. 
B) Electrophilic substitution reaction. 
C) Oxidation reaction. 
D) Reduction reaction. 
E) None of the above. 
A) Free radical reaction. 
B) Electrophilic substitution reaction. 
C) Oxidation reaction. 
D) Reduction reaction. 
E) None of the above.

Question 2

Zymogens are inactive enzyme precursors which are made active by

Accepted Answer

A) a change in folding only. 
B) selective proteolysis. 
C) methylation of particular residues. 
D) a change in pH. 
A) a change in folding only. 
B) selective proteolysis. 
C) methylation of particular residues. 
D) a change in pH.

Question 3

Acid-base catalysis is estimated to accelerate a typical enzymatic reaction by what factor?

Accepted Answer

A) 1 to 2 fold increase. 
B) 10 to 100 fold increase. 
C) 106 fold increase. 
D) 1023 fold increase. 
A) 1 to 2 fold increase. 
B) 10 to 100 fold increase. 
C) 106 fold increase. 
D) 1023 fold increase.

Question 4

Induced fit studies by Koshland using the enzyme hexokinase showed that there are enzyme forms

Accepted Answer

A) which react with the hydroxyl group of water. 
B) which react only with ATP and glucose present together. 
C) which are hydrophobic,excluding the competing hydroxyl group from water. 
D) with and without glucose bound to each. 
E) that hydrolyze ATP. 
A) which react with the hydroxyl group of water. 
B) which react only with ATP and glucose present together. 
C) which are hydrophobic,excluding the competing hydroxyl group from water. 
D) with and without glucose bound to each. 
E) that hydrolyze ATP.

Question 5

Which mode(s)of catalysis is/are classified as chemical effects? 
1. Transition state stabilization
2. Acid-base catalysis
3. Covalent catalysis
4. Proximity effect

Accepted Answer

A) 3 only. 
B) 1,2 and 3. 
C) 2 and 3. 
D) All of them. 
A) 3 only. 
B) 1,2 and 3. 
C) 2 and 3. 
D) All of them.

Question 6

On the energy diagram below,which point represents an intermediate?

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 7

Which bond in the polysaccharide shown is cleaved by lysozyme?

Accepted Answer

A) A 
B) B 
C) C 
D) D 
A) A 
B) B 
C) C 
D) D

Question 8

A detailed description of a chemical reaction in terms of the molecular,atomic or subatomic events is called the reaction ________.

Accepted Answer

A) mechanism 
B) pathway 
C) primary sequence 
D) motif 
A) mechanism 
B) pathway 
C) primary sequence 
D) motif

Question 9

The relative orientation of colliding molecules only affects reactions rates when the energy during impact is low.If the energy of impact is high enough,orientation is unimportant.

Accepted Answer

A) True 
 B)False

Question 10

What is the biological function of lysozyme?

Accepted Answer

A) Converts trypsinogen to trypsin. 
B) Is a ligase that accelerates the polymerization of glycogen. 
C) It regulates vascular constriction in chickens. 
D) Hydrolyzes polysaccharides of bacterial cell walls. 
A) Converts trypsinogen to trypsin. 
B) Is a ligase that accelerates the polymerization of glycogen. 
C) It regulates vascular constriction in chickens. 
D) Hydrolyzes polysaccharides of bacterial cell walls.

Question 11

Which graph might you expect for the pH profile of an enzyme's activity if the only ionizable residue in the active site is aspartate?

Accepted Answer

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

Question 12

The graph shows the rate of catalysis versus pH for an enzyme-catalyzed reaction.What conclusion can be made from the graph?

Accepted Answer

A) The enzyme is completely denatured by pHs greater than 8 or less than 5. 
B) The substrate has four ionizable groups. 
C) At pH 6.2 all ionizable groups in the active site are protonated. 
D) The enzyme has an acidic and a basic amino acid in the active site. 
E) The enzyme has only one protonatable residue in the active site. 
A) The enzyme is completely denatured by pHs greater than 8 or less than 5. 
B) The substrate has four ionizable groups. 
C) At pH 6.2 all ionizable groups in the active site are protonated. 
D) The enzyme has an acidic and a basic amino acid in the active site. 
E) The enzyme has only one protonatable residue in the active site.

Question 13

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 14

Cleavage of a C-C bond produces a carbanion that ________ both electrons and a carbocation that ________ both electrons.

Accepted Answer

A) loses;loses 
B) loses;keeps 
C) keeps;loses 
D) keeps;keeps 
A) loses;loses 
B) loses;keeps 
C) keeps;loses 
D) keeps;keeps

Question 15

Pepsin and trypsin are produced in the pancreas as zymogens.What might result if these two enzymes were not produced in the pancreas as zymogens,but as active pepsin and trypsin?

Accepted Answer

A) They would not be transported to the intestine because of their native charge. 
B) They would not be folded properly by their chaperone molecules. 
C) They would associate into inactive oligomeric forms. 
D) They would begin to degrade and damage pancreatic proteins. 
A) They would not be transported to the intestine because of their native charge. 
B) They would not be folded properly by their chaperone molecules. 
C) They would associate into inactive oligomeric forms. 
D) They would begin to degrade and damage pancreatic proteins.

Question 16

In this reaction,the carbon is ________.

Accepted Answer

A) oxidized 
B) reduced 
C) neutralized 
D) hydrolyzed 
A) oxidized 
B) reduced 
C) neutralized 
D) hydrolyzed

Question 17

Match each of these terms with the correct description:
-S is bound covalently to the enzyme

Accepted Answer

A) induced fit 
B) proximity effect 
C) covalent catalysis 
D) diffusion-controlled reaction 
E) acid-base catalysis 
A) induced fit 
B) proximity effect 
C) covalent catalysis 
D) diffusion-controlled reaction 
E) acid-base catalysis

Question 18

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 pKa's 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 pKa's 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 19

The movement of ________ is key to understanding chemical and enzymatic reactions.

Accepted Answer

A) neutrons 
B) electrons 
C) nucleophiles 
D) electrophiles 
A) neutrons 
B) electrons 
C) nucleophiles 
D) electrophiles

Question 20

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

Accepted Answer

A) True 
 B)False

Exam 6: Mechanisms of Enzymes

How is the half-reaction Cu²+ + 2e- → Cu classified?

Zymogens are inactive enzyme precursors which are made active by

Acid-base catalysis is estimated to accelerate a typical enzymatic reaction by what factor?

Induced fit studies by Koshland using the enzyme hexokinase showed that there are enzyme forms

Which mode(s)of catalysis is/are classified as chemical effects? 1. Transition state stabilization 2. Acid-base catalysis 3. Covalent catalysis 4. Proximity effect

On the energy diagram below,which point represents an intermediate?

Which bond in the polysaccharide shown is cleaved by lysozyme?

A detailed description of a chemical reaction in terms of the molecular,atomic or subatomic events is called the reaction ________.

The relative orientation of colliding molecules only affects reactions rates when the energy during impact is low.If the energy of impact is high enough,orientation is unimportant.

What is the biological function of lysozyme?

Which graph might you expect for the pH profile of an enzyme's activity if the only ionizable residue in the active site is aspartate?

The graph shows the rate of catalysis versus pH for an enzyme-catalyzed reaction.What conclusion can be made from the graph?

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

Cleavage of a C-C bond produces a carbanion that ________ both electrons and a carbocation that ________ both electrons.

Pepsin and trypsin are produced in the pancreas as zymogens.What might result if these two enzymes were not produced in the pancreas as zymogens,but as active pepsin and trypsin?

In this reaction,the carbon is ________.

Match each of these terms with the correct description: -S is bound covalently to the enzyme

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?

The movement of ________ is key to understanding chemical and enzymatic reactions.

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

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

Cleavage of a C-C bond produces a carbanion that both electrons and a carbocation that both electrons.