Storage Mechanisms and Control in Carbohydrate Metabolism

Question 1

Which of the following statements concerning branched polymers like glycogen is false?
a. Branched polymers are more accessible to enzymes since they bond more water.
b. All of the reducing ends of the branched polymer are available to release glucose.
c. All of the non-reducing ends of the branched polymer are available to release glucose.
d. A branched polymer like glycogen is more compact and stores more glucose molecules in a given volume.

Answer 1

b

Question 2

What is the average chain length of the branches in glycogen?
a. 6 glucose residues
b. 13 glucose residues
c. 25 glucose residues
d. 50 glucose residues
e. 100 glucose residues

Answer 2

b

Question 3

Glycogen is mainly found in
a. liver and muscle.
b. liver and brain.
c. muscle and brain.
d. liver, muscle, and brain.
e. adipose tissue

Answer 3

a

Question 4

Which of the following best describes how liver supplies other tissues with the glucose it releases from its stored
glycogen?
a. It releases short chains of glucose residues into the blood.
b. It releases glucose-1-phosphate into the blood.
c. It releases glucose-6-phosphate into the blood.
d. It releases glucose into the blood.
e. It releases glucose in the form of lipopolysaccharides

Answer 4

d

Question 5

The enzyme that catalyzes the interconversion of glucose-1-phosphate and glucose-6-phosphate is
a. a hydrolase.
b. a phosphorylase.
c. a mutase.
d. a dehydrogenase.
e. an epimerase

Answer 5

c

Question 6

Glycolysis that starts with glycogen instead of glucose can be considered to have a higher energy yield because:
a. Phosphorolysis reactions cleave bonds with phosphate instead of water.
b. Phosphorylase is a better enzyme than hexokinase
c. Phosphorylase produces a glucose phosphate without spending an ATP to do it
d. All of these
e. None of these is true because glycolysis starting from glycogen does not have a higher energy yield

Answer 6

c

Question 7

Which enzyme cleaves the α(1 → 6) bonds in glycogen?
a. glycogen phosphorylase
b. debranching enzyme
c. phosphoglucomutase
d. glycogen synthase
e. None of these because there are no α(1 → 6) bonds in glycogen.

Answer 7

b

Question 8

What kind of reaction is used to release glucose units from glycogen?
a. hydrolysis
b. phosphorolysis
c. dehydration
d. oxidation
e. dehydrogenation

Answer 8

b

Question 9

The enzyme glycogen phosphorylase catalyzes a reaction in
a. the formation of glycogen from glucose.
b. glycogen breakdown.
c. gluconeogenesis.
d. the pentose phosphate pathway.
e. glycolysis

Answer 9

b

Question 10

If an individual lacked the debranching enzyme, the effect would be:
a. the individual could not make glycogen
b. the individual could make glycogen but not store it
c. the individual would not be able to utilize any glucose from glycogen
d. the individual would not be able to completely break down a glycogen molecule
e. none of these

Answer 10

d

Question 11

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

Answer 11

d

Question 12

The compound uridine diphosphate glucose (UDPG) plays a role in
a. glycogen breakdown.
b. glycogen synthesis.
c. glycolysis.
d. gluconeogenesis.
e. none of these

Answer 12

b

Question 13

The activity of glycogen phosphorylase depends on
a. allosteric control
b. covalent modification
c. both of these
d. neither of these

Answer 13

c

Question 14

Glucose-6-phosphatase activity is found associated with the endoplasmic reticulum.
a. True
b. False

Answer 14

a

Question 15

How are the branches in glycogen produced?
a. A branching enzyme catalyses the addition of a single glucose unit via an α(1,6) bond to glycogen from a glucose-1-phosphate, releasing Pi.

b. A branching enzyme catalyses the addition of a single glucose unit via an α(1,6) bond to glycogen from a glucose-6-phosphate, releasing Pi.

c. A branching enzyme catalyses the addition of a single glucose unit via an α(1,6) bond to glycogen from a glucose-UDP, releasing UDP.

d. A branching enzyme moves a short chain of several glucose units from a linear α(1,4) section of glycogen to make a new α(1,6) branch point.

Answer 15

d

Question 16

UDP-glucose pyrophosphorylase works by this mechanism:
a. It adds a phosphate group to glucose from UTP, leaving behind UDP.
b. It adds a UMP molecule to glucose-1-phosphate by splitting out pyrophosphate.
c. It adds a pyrophosphate group to glucose, using UTP.
d. It adds a UDP molecule to glucose by splitting out phosphate.
e. None of these

Answer 16

b

Question 17

Which of the following reactions occur when a single glucose residue is transferred from UDP-glucose to a growing
glycogen molecule?
a. UDP is released.
b. The glucose can be attached to a #4 carbon atom in the glycogen molecule.
c. UDP is released and the glucose is attached to a #4 carbon.
d. All of these events can occur when a single glucose residue is added.

Answer 17

d

Question 18

Glycogen phosphorylase
a. exists in two forms, phosphorylase a and phosphorylase b
b. responds differently to allosteric effectors in its phosphorylated and dephosphorylated forms
c. both of these
d. neither of these

Answer 18

c

Question 19

Starting from glucose and UTP and ATP, how many high-energy bonds are broken/consumed to add that glucose to a
glycogen molecule?
a. 1
b. 2
c. 3
d. 4
e. The answer cannot be determined form the information given.

Answer 19

b

Question 20

When glycogen synthase is phosphorylated
a. its activity decreases.
b. its activity increases.
c. its activity is unaffected.
d. none of these because that enzyme doesn’t get phosphorylated.

Answer 20

a

Question 21

When glycogen phosphorylase is phosphorylated
a. its activity decreases.
b. its activity increases.
c. its activity is unaffected.
d. none of these because that enzyme doesn’t get phosphorylated.

Answer 21

b

Question 22

Where is the enzyme glucose-6-phosphatase located?
a. cytosol
b. mitochondria
c. endoplasmic reticulum
d. nucleus
e. none of these

Answer 22

c

Question 23

Glycogen phosphorylase and glycogen synthase
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

Answer 23

a

Question 24

Glycogen synthase and glycogen phosphorylase
a. are modified by the same enzymes
b. are not subject to allosteric control
c. are not subject to covalent modification
d. none of these

Answer 24

a

Question 25

Hydrolysis of pyrophosphate is an important energy driving force in the synthesis of glycogen.
a. True
b. False

Answer 25

a

Question 26

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

Answer 26

c

Question 27

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

Answer 27

a

Question 28

Branching and debranching enzymes use the exact same mechanism to add and remove the branches of the glycogen
polymer.
a. True
b. False

Answer 28

b

Question 29

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

Answer 29

a

Question 30

Generally speaking, the same mechanisms that activate glycogen phosphorylase will turn off glycogen synthase.
a. True
b. False

Answer 30

a

Question 31

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

Answer 31

d

Question 32

Glycogen loading is particularly advantageous for providing energy for long distance athletic events, such as running the marathon.
a. True
b. False

Answer 32

b

Question 33

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

Answer 33

a

Question 34

Which of the following molecules does not directly regulate the activity of glycogen synthase?
a. Glucose
b. Glucose-6-phosphate
c. AMP
d. ATP
e. Concentration of all of these affects glycogen synthase.

Answer 34

a

Question 35

There is as much energy used to add a phosphate group by means of phosphorolysis, as the energy required adding a
phosphate using ATP.
a. True
b. False

Answer 35

b

Question 36

Gluconeogenesis is the synthesis of
a. glucose from non-carbohydrate precursors
b. glycogen from glucose
c. pyruvate from glucose
d. fatty acids from glucose
e. glucose from glycogen

Answer 36

a

Question 37

Gluconeogenesis differs from glycolysis because
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

Answer 37

d

Question 38

Which enzyme is used in gluconeogenesis, but NOT in glycolysis?
a. PEP carboxykinase
b. enolase
c. phosphohexose isomerase
d. 3-phosphoglycerate dehydrogenase

Answer 38

a

Question 39

The enzyme pyruvate carboxylase
a. is not subject to allosteric control
b. requires biotin for activity
c. catalyzes a reaction that does not require ATP
d. is inhibited by acetyl-CoA

Answer 39

b

Question 40

In which cellular compartment is pyruvate carboxylase found?
a. cytosol
b. mitochondria
c. endoplasmic reticulum
d. nucleus

Answer 40

b

Question 41

Which of the following statements concerning biotin and gluconeogenesis is false?
a. Biotin is used to add CO2 to certain intermediates in gluconeogenesis.
b. CO2 is incorporated into the glucose product.
c. Biotin is capable of binding covalently to CO2.
d. Biotin helps synthesize an important precursor of phosphoenolpyruvate.
e. ATP hydrolysis is required to attach CO2 to biotin.

Answer 41

b

Question 42

The regulatory enzymes in gluconeogenesis are
a. hexokinase, phosphofructokinase, and pyruvate kinase
b. glucose-6-kinase, aldolase, and enolase
c. glucose-6-phosphatase, fructose-1,6-bisphosphatase, pyruvate carboxylase, and phosphoenolpyruvate
carboxykinase
d. pyruvate carboxylase, aldolase, and phosphofructokinase

Answer 42

c

Question 43

In gluconeogenesis, the initial reaction converts pyruvate to
a. oxaloacetate
b. acetyl-CoA
c. phosphoenolpyruvate
d. lactate
e. glucose

Answer 43

a

Question 44

The first reaction of gluconeogenesis is
a. an oxidative decarboxylation
b. a carboxylation
c. a redox reaction
d. a phosphate transfer

Answer 44

b

Question 45

Which nucleotide triphosphate is hydrolyzed in the conversion of oxaloacetate to phosphoenolpyruvate?
a. ATP
b. GTP
c. CTP
d. UTP
e. No nucleotide triphosphate is hydrolysed.

Answer 45

b

Question 46

The NADH used for the reduction reactions during gluconeogenesis usually come from this reaction:
a. Gylceraldehyde-3-phosphate dehydrogenase.
b. Malate dehydrogenase activity in the cytoplasm.
c. Pyruvate carboxylase activity in the mitochondria.
d. A variety of reactions which produce NADH in the mitochondria.
e. None of these, since it is NAD+
that is used in gluconeogenesis.

Answer 46

b

Question 47

Which of the following is 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

Answer 47

c

Question 48

How many ATP equivalents are expended to convert 2 pyruvates to 1 glucose?
a. 2
b. 4
c. 6
d. 8

Answer 48

c

Question 49

It is impossible to reverse any kinase reaction under physiological conditions.
a. True
b. False

Answer 49

a

Question 50

In general, opposing pathways, such as glycolysis and gluconeogenesis are not exact reversals of each other.
a. True
b. False

Answer 50

a

Question 51

The formation and breakdown of fructose 2,6-bisphosphate
a. is catalyzed by the same protein dependant upon whether it is phosphorylated or not.
b. is catalyzed by the same protein dependant allosteric regulators.
c. is catalyzed by different proteins.
d. none of these

Answer 51

a

Question 52

High concentrations of fructose-2,6-bisphopshate
a. stimulate glycolysis and inhibit gluconeogenesis.
b. inhibit glycolysis and stimulate gluconeogenesis.
c. stimulate both glycolysis and gluconeogenesis.
d. inhibit both glycolysis and gluconeogenesis.
e. none of these

Answer 52

a

Question 53

The activity of the enzyme fructose 1,6-bisphosphatase is
a. inhibited by ATP.
b. stimulated by AMP.
c. inhibited by fructose 2,6-bisphosphate.
d. not subject to allosteric control.

Answer 53

c

Question 54

In the process of substrate cycling
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.

Answer 54

d

Question 55

The molecule fructose 2,6-bisphosphate:
a. is an intermediate in glycolysis
b. is an intermediate of gluconeogenesis but not glycolysis
c. does not exist
d. is an important regulatory molecule in the control of carbohydrate metabolism
e. none of these

Answer 55

d

Question 56

The enzyme glucose-6-phosphatase is only found in cells which have this function or ability:
a. Ability to utilize glucose anaerobically.
b. Ability to replenish the levels of glucose in the blood.
c. Glycogen storage.
d. Ability to produce lactic acid as an end product of metabolism.
e. Glucose-6-phosphatase activity is found in almost all types of cells.

Answer 56

d

Question 57

If you’re running away from a bear,
a. both your liver cells and my leg muscle cells will be running glycolysis.
b. both your liver cells and my leg muscle cells will be running gluconeogenesis.
c. your liver cells will be running gluconeogenesis and your leg muscle cells will be running glycolysis.
d. your liver cells will be running glycolysis and your leg muscle cells will be running gluconeogenesis.

Answer 57

c

Question 58

In the Cori cycle
a. lactic acid is transported from the liver to muscle by the blood.
b. lactic acid is transported from the liver to the kidneys by the blood.
c. glycolysis takes place in muscle and gluconeogenesis in the liver.
d. glycolysis takes place in the liver and gluconeogenesis in muscle.
e. none of these

Answer 58

c

Question 59

The process called substrate cycling is used to describe this process:
a. Freely reversible reactions.
b. Recycling of vitamins as catalysts in metabolism
c. Situations where there are two different enzymes used to reverse a specific step in a metabolic pathway.
d. Metabolic pathways which run in cycles and regenerate the initial molecule.
e. None of these answers describes substrate cycling.

Answer 59

c

Question 60

The Cori cycle involves the following:
a. Conversion of lactate produced in the liver by regeneration of glucose in the muscle.
b. Conversion of pyruvate produced in the muscle by regeneration of glucose in the liver.
c. Conversion of lactate produced in the muscle by regeneration of glucose in the liver.
d. Conversion of NADH produced in the muscle by regeneration of glucose in the liver.
e. The Cori cycle involves a different pathway from any of these.

Answer 60

c

Question 61

Which of the following mechanisms can be used to regulate metabolic pathways?
a. Allosteric activators and inhibitors.
b. Covalent modifications of enzymes.
c. Use of separate enzymes at a given point in the forward and backward pathways.
d. Regulation of the genes for the enzymes used in the pathway.
e. All of these are used to regulate metabolism.

Answer 61

e

Question 62

The liver contains a special enzyme, hexokinase, to act as a backup for glucokinase when the glucose levels in the
body get very high.
a. True
b. False

Answer 62

b

Question 63

Which of the following is NOT a hormone involved in the control of carbohydrate metabolism?
a. epinephrine
b. glucagon
c. insulin
d. phosphofructokinase

Answer 63

d

Question 64

Which of the following occurs when insulin is released?
a. insulin binds to receptors on cell surfaces
b. a protein kinase cascade is begun that leads to glycogen synthesis
c. insulin stimulates the GLUT4 transport protein system in muscle cells
d. glucose transporters move glucose out of the blood and into the cell
e. all of these

Answer 64

e

Question 65

Which of the following happens when epinephrine and glucagon are released
a. glycogen phosophorylase is activated and glycogen synthase is inhibited
b. glycogen phosphorylase and glycogen synthase are activated
c. glycogen phosphorylase and glycogen synthase are inhibited
d. glycogen phosphorylase is inhibited and glycogen synthase is activated
e. none of these

Answer 65

a

Question 66

Which of the following hormone’s main function is to raise the level of blood glucose?
a. epinephrine
b. insulin
c. glucagon
d. none of these raises blood glucose

Answer 66

c

Question 67

The primary function of the pentose phosphate pathway is
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.

Answer 67

b

Question 68

During the pentose phosphate pathway (glucose-6-P → ribose-5-P), is there a net oxidation of the substrate carbon
atoms?
a. Yes.
b. No.
c. It depends on whether the process is under aerobic or anaerobic conditions.
d. It depends on the species doing the process.
e. It depends on whether the glucose goes through the oxidative part of the pathway or not.

Answer 68

e

Question 69

What kind of enzyme catalyzes the following reaction?
ribose-5-P ↔ ribulose-5-P
a. transketolase
b. epimerase
c. transaldolase
d. isomerase

Answer 69

d

Question 70

What kind of enzyme catalyzes the reaction
ribulose-5-P ↔ xylulose-5-P?
a. transketolase
b. epimerase
c. transaldolase
d. isomerase

Answer 70

b

Question 71

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

Answer 71

d

Question 72

In one normal cycle of the pentose phosphate pathway, the enzyme transaldolase is used twice and the enzyme
transketolase is used once.
a. True
b. False

Answer 72

b

Question 73

The oxidative reactions of the pentose phosphate pathway
a. produce NADPH rather than NADH.
b. require biotin.
c. require coenzyme A.
d. require thiamine pyrophosphate.

Answer 73

a

Question 74

The conversion of ribulose 5-phosphate to xylulose 5-phosphate is
a. a dehydration
b. an oxidation
c. a reduction
d. an epimerization

Answer 74

d

Question 75

A characteristic of the reaction catalyzed by transaldolase is
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

Answer 75

a

Question 76

Which of the following molecules is not a product of the pentose phosphate pathway?
a. NADPH
b. ribose-5-phosphate
c. glycerate-3-phosphate
d. xylulose-5-phosphate

Answer 76

c

Question 77

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.
a. True
b. False

Answer 77

a

Question 78

The enzyme phosphopentose isomerase is characterized by all the following except
a. it catalyzes the interconversion of ribose-5-phosphate and ribulose-5-phosphate
b. there is no requirement for ATP
c. it converts a ketose to an aldose
d. it catalyzes an inversion of configuration at carbon-3

Answer 78

d

Question 79

In addition to pentoses, the pentose phosphate pathway involves sugars of all these sizes except:
a. 3 carbons
b. 4 carbons
c. 6 carbons
d. 7 carbons
e. All of these sizes are used in this pathway

Answer 79

e

Question 80

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

Answer 80

e

Question 81

All of the following sugar rearrangements are part of the pentose phosphate pathway, except.
a. C5 + C5 → C7 + C3
b. C5 + C5 → C6 + C4
c. C7 + C3 → C6 + C4
d. C5 + C4 → C6 + C3
e. All of these rearrangements occur in the pentose phosphate pathway.

Answer 81

b

Question 82

Hemolytic anemia is associated with the pentose phosphate pathway because:
a. a deficiency of this pathway leads to a lack of NADPH in red blood cells
b. NADPH is required to reduce glutathione
c. Red blood cells have minimal resources for maintaining an oxidative balance
d. all of these

Answer 82

d

Question 83

Explain the advantage of a branched-chain structure of glycogen over a linear polymer.

Answer 83

The highly branched structure of glycogen makes it possible for several glucose residues to be
released at once to meet energy needs. This would not be possible with a linear polymer. The red
dots indicate the terminal glucose residues that are released from glycogen. The more branch points
there are, the more terminal residues are available at one time.

Question 84

Identify the enzyme that catalyzes the isomerization of glucose-1-phosphate to glucose 6-phosphate.
a. Phosphogluconolactonase
b. Phosphoglucoisomerase
c. Phosphoglucokinase
d. Phosphoglucomutase

Answer 84

d

Question 85

Identify the enzyme that catalyzes the growth of glycogen chains.
a. Glucose oxidase
b. Glycogen synthase
c. L-gulonolactone oxidase
d. Phosphoglucomutase

Answer 85

b

Question 86

Which of the following hormones is responsible for initiating the “fight or flight” response on a very short time scale?
a. Galanin
b. Erythropoietin
c. Glucagon
d. Epinephrine

Answer 86

d

Question 87

Identify the type of metabolic control mechanism in which the amount of enzyme present is increased by protein
synthesis.
a. Allosteric control
b. Covalent modification
c. Substrate cycles
d. Genetic control

Answer 87

d