Question 1

Which of the following best describes the function of debranching enzyme?

Accepted Answer

A)  It simply cleaves α(1 → 6) bonds in glycogen via phosphorolysis. 
B)  It transfers a set of three glucose residues from a limit branch and then cleaves the α(1 → 6) bond via phosphorylsis. 
C)  It simply cleaves α(1 → 6) bonds in glycogen via hydrolysis. 
D)  It transfers a set of three glucose residues from a limit branch and then cleaves the α(1 → 6) bond via hydrolysis. 
E)  none of these describes the enzyme's function 
A)  It simply cleaves α(1 → 6) bonds in glycogen via phosphorolysis. 
B)  It transfers a set of three glucose residues from a limit branch and then cleaves the α(1 → 6) bond via phosphorylsis. 
C)  It simply cleaves α(1 → 6) bonds in glycogen via hydrolysis. 
D)  It transfers a set of three glucose residues from a limit branch and then cleaves the α(1 → 6) bond via hydrolysis. 
E)  none of these describes the enzyme's function

Question 2

The primary function of the pentose phosphate pathway is

Accepted Answer

A)  to synthesize NAD+ and pentose phosphates. 
B)  to synthesize NADPH and pentose phosphates. 
C)  to produce NADH. 
D)  to convert pentose phosphates to metabolic intermediates for oxidative phosphorylation. 
A)  to synthesize NAD+ and pentose phosphates. 
B)  to synthesize NADPH and pentose phosphates. 
C)  to produce NADH. 
D)  to convert pentose phosphates to metabolic intermediates for oxidative phosphorylation.

Question 3

Which of the following molecules is not a product of the pentose phosphate pathway?

Accepted Answer

A)  NADPH 
B)  ribose-5-phosphate 
C)  glycerate-3-phosphate 
D)  xylulose-5-phosphate 
A)  NADPH 
B)  ribose-5-phosphate 
C)  glycerate-3-phosphate 
D)  xylulose-5-phosphate

Question 4

The same enzymes are responsible for covalent modifications of both glycogen synthase and glycogen phosphorylase in regulating their activity.

Accepted Answer

A) True 
 B)False

Question 5

Which of the following is not a control mechanism for glycogen phosphorylase?

Accepted Answer

A)  Covalent modification. 
B)  Inhibition by glucose. 
C)  Subunit association and dissociation. 
D)  Allosteric stimulation by AMP. 
E)  All of these mechanisms regulate the activity of glycogen synthase. 
A)  Covalent modification. 
B)  Inhibition by glucose. 
C)  Subunit association and dissociation. 
D)  Allosteric stimulation by AMP. 
E)  All of these mechanisms regulate the activity of glycogen synthase.

Question 6

The first reaction of gluconeogenesis is

Accepted Answer

A)  an oxidative decarboxylation 
B)  a carboxylation 
C)  a redox reaction 
D)  a phosphate transfer 
A)  an oxidative decarboxylation 
B)  a carboxylation 
C)  a redox reaction 
D)  a phosphate transfer

Question 7

The vitamin thiamine is important in transferring all of these types of groups, except:

Accepted Answer

A)  2-carbon sugar fragments 
B)  3-carbon sugar fragments 
C)  4-carbon sugar fragments 
D)  Sugar fragments which contain a carbonyl group (C=O). 
E)  Thiamine can transfer all of these types of groups. 
A)  2-carbon sugar fragments 
B)  3-carbon sugar fragments 
C)  4-carbon sugar fragments 
D)  Sugar fragments which contain a carbonyl group (C=O). 
E)  Thiamine can transfer all of these types of groups.

Question 8

Gluconeogenesis differs from glycolysis because

Accepted Answer

A)  the irreversible steps of glycolysis are bypassed 
B)  different enzymes are involved 
C)  biotin is required for gluconeogenesis and not for glycolysis 
D)  all of these 
E)  none of these 
A)  the irreversible steps of glycolysis are bypassed 
B)  different enzymes are involved 
C)  biotin is required for gluconeogenesis and not for glycolysis 
D)  all of these 
E)  none of these

Question 9

Of the various forms of glycogen phosphorylase, the most active would be:

Accepted Answer

A)  the phosphorylated R form 
B)  the unphosphorylated R form 
C)  the phosphorylated T form 
D)  the unphosphorylated T form 
E)  all of the forms have the same activity 
A)  the phosphorylated R form 
B)  the unphosphorylated R form 
C)  the phosphorylated T form 
D)  the unphosphorylated T form 
E)  all of the forms have the same activity

Question 10

Glycogen phosphorylase and glycogen synthase

Accepted Answer

A)  are not activated simultaneously 
B)  are activated simultaneously under special circumstances 
C)  can be activated simultaneously under any circumstances 
D)  are involved in catalysis of the same process 
A)  are not activated simultaneously 
B)  are activated simultaneously under special circumstances 
C)  can be activated simultaneously under any circumstances 
D)  are involved in catalysis of the same process

Question 11

Properly used, glycogen loading by athletes is a safe process.

Accepted Answer

A) True 
 B)False

Question 12

The activity of the enzyme fructose 1,6-bisphosphatase is

Accepted Answer

A)  inhibited by ATP. 
B)  stimulated by AMP. 
C)  inhibited by fructose 2,6-bisphosphate. 
D)  not subject to allosteric control. 
A)  inhibited by ATP. 
B)  stimulated by AMP. 
C)  inhibited by fructose 2,6-bisphosphate. 
D)  not subject to allosteric control.

Question 13

The conversion of ribulose 5-phosphate to xylulose 5-phosphate is

Accepted Answer

A)  a dehydration 
B)  an oxidation 
C)  a reduction 
D)  an epimerization 
A)  a dehydration 
B)  an oxidation 
C)  a reduction 
D)  an epimerization

Question 14

Which of the following is true?

Accepted Answer

A)  Gluconeogenesis from pyruvate involves simple reversal of all of the glycolysis reactions, except for the reactions that consumed ATP during catabolism. 
B)  Anabolic reactions are usually the reversal of catabolic ones 
C)  In gluconeogenesis, the effective reversal of the glycolytic reactions of hexokinase and phosphofructokinase involve the same sugar molecules but not the exact set of substrates and products 
D)  all of these are true 
A)  Gluconeogenesis from pyruvate involves simple reversal of all of the glycolysis reactions, except for the reactions that consumed ATP during catabolism. 
B)  Anabolic reactions are usually the reversal of catabolic ones 
C)  In gluconeogenesis, the effective reversal of the glycolytic reactions of hexokinase and phosphofructokinase involve the same sugar molecules but not the exact set of substrates and products 
D)  all of these are true

Question 15

A characteristic of the reaction catalyzed by transaldolase is

Accepted Answer

A)  transfer of a three-carbon unit 
B)  transfer of a two-carbon unit 
C)  a requirement for TPP as a coenzyme 
D)  an energy requirement for oxidative decarboxylation 
A)  transfer of a three-carbon unit 
B)  transfer of a two-carbon unit 
C)  a requirement for TPP as a coenzyme 
D)  an energy requirement for oxidative decarboxylation

Question 16

Which of the following statements concerning the initial phase of the pentose phosphate pathway is false?

Accepted Answer

A)  A CO2 molecule is released from glucose. 
B)  Two molecules of NADPH are produced per glucose. 
C)  Ribulose-5-phosphate is produced by an oxidative decarboxylation of 6-phosphogluconate. 
D)  The process reduces glucose-6-phosphate. 
A)  A CO2 molecule is released from glucose. 
B)  Two molecules of NADPH are produced per glucose. 
C)  Ribulose-5-phosphate is produced by an oxidative decarboxylation of 6-phosphogluconate. 
D)  The process reduces glucose-6-phosphate.

Question 17

Which of the following is not an advantage that glycogen provides to muscle cells in which it is stored?

Accepted Answer

A)  It is available for quick energy spurts. 
B)  It requires no energy to mobilize the glucose residues for metabolism. 
C)  It gives anaerobic metabolism a boost. 
D)  It draws more water into the cells than glucose would. 
E)  All of these are advantages that glycogen provides to muscle cells. 
A)  It is available for quick energy spurts. 
B)  It requires no energy to mobilize the glucose residues for metabolism. 
C)  It gives anaerobic metabolism a boost. 
D)  It draws more water into the cells than glucose would. 
E)  All of these are advantages that glycogen provides to muscle cells.

Question 18

In the process of substrate cycling

Accepted Answer

A)  different organs are responsible for the synthesis and breakdown of the same substance. 
B)  there is no net consumption of ATP. 
C)  allosteric control is not involved. 
D)  different enzymes, subject to independent control, are responsible for the synthesis and breakdown of the same substance. 
A)  different organs are responsible for the synthesis and breakdown of the same substance. 
B)  there is no net consumption of ATP. 
C)  allosteric control is not involved. 
D)  different enzymes, subject to independent control, are responsible for the synthesis and breakdown of the same substance.

Question 19

What kind of enzyme catalyzes the reaction ribulose-5-P ↔ xylulose-5-P?

Accepted Answer

A)  transketolase 
B)  epimerase 
C)  transaldolase 
D)  isomerase 
A)  transketolase 
B)  epimerase 
C)  transaldolase 
D)  isomerase

Question 20

Control of the entry of glucose or fructose into the oxidative portions of the pentose phosphate pathway is mostly dependent on a cell's need for NADPH, rather than on the cell's need for pentoses.

Accepted Answer

A) True 
 B)False

Exam 18: Storage Mechanisms and Control in Carbohydrate Metabolism

Which of the following best describes the function of debranching enzyme?

The primary function of the pentose phosphate pathway is

Which of the following molecules is not a product of the pentose phosphate pathway?

The same enzymes are responsible for covalent modifications of both glycogen synthase and glycogen phosphorylase in regulating their activity.

Which of the following is not a control mechanism for glycogen phosphorylase?

The first reaction of gluconeogenesis is

The vitamin thiamine is important in transferring all of these types of groups, except:

Gluconeogenesis differs from glycolysis because

Of the various forms of glycogen phosphorylase, the most active would be:

Glycogen phosphorylase and glycogen synthase

Properly used, glycogen loading by athletes is a safe process.

The activity of the enzyme fructose 1,6-bisphosphatase is

The conversion of ribulose 5-phosphate to xylulose 5-phosphate is

Which of the following is true?

A characteristic of the reaction catalyzed by transaldolase is

Which of the following statements concerning the initial phase of the pentose phosphate pathway is false?

Which of the following is not an advantage that glycogen provides to muscle cells in which it is stored?

In the process of substrate cycling

What kind of enzyme catalyzes the reaction ribulose-5-P ↔ xylulose-5-P?

Control of the entry of glucose or fructose into the oxidative portions of the pentose phosphate pathway is mostly dependent on a cell's need for NADPH, rather than on the cell's need for pentoses.

Biochemistry and the Organization of Cells

Water: the Solvent for Biochemical Reactions

Amino Acids and Peptides

The Three-Dimensional Structure of Proteins

Protein Purification and Characterization Techniques

The Behavior of Proteins: Enzymes

The Behavior of Proteins: Enzymes, Mechanisms, and Control

Lipids and Proteins Are Associated in Biological Membranes

Nucleic Acids: How Structure Conveys Information

Biosynthesis of Nucleic Acids: Replication

Transcription of the Genetic Code: Biosynthesis of RNA

Protein Synthesis: Translation of the Genetic Message

Nucleic Acid Biotechnology Techniques

Viruses, Cancer, and Immunology

The Importance of Energy Changes and Electron Transfer in Metabolism

Carbohydrates

Glycolysis

The Citric Acid Cycle

Electron Transport and Oxidative Phosphorylation

Lipid Metabolism

Photosynthesis

The Metabolism of Nitrogen

Integration of Metabolism: Cellular Signaling

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