Storage Mechanism and Control Flashcards by Ray Mark

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.

B. All of the reducing ends of the branched polymer are available
to release glucose.

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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

13 glucose residues

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Glycogen is mainly found in
A. liver and muscle.
B. liver and brain.
C. muscle and brain.
D. liver, muscle, and brain.

liver and muscle

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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.

It releases glucose into the blood

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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.

a mutase

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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

Phosphorylase produces a glucose phosphate without spending an ATP to do it

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Which enzyme cleaves the a(1 6) bonds in glycogen?
A. glycogen phosphorylase
B. debranching enzyme
C. phosphoglucomutase
D. glycogen synthase
E. There are no a(1 6) bonds in glycogen.

debranching enzyme

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What kind of reaction is used to release glucose units from glycogen?
A. hydrolysis
B. phosphorolysis
C. dehydration
D. oxidation

phosphorolysis

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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.

glycogen breakdown

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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

the individual would not be able to completely break down a glycogen molecule

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Which of the following best describes the function of debranching
enzyme?
A. It simply cleaves a(1 6) bonds in glycogen via phosphorolysis.
B. It transfers a set of three glucose residues from a limit branch
and then cleaves the a(1 6) bond via phosphorylsis.
C. It simply cleaves a(1 6) bonds in glycogen via hydrolysis.
D. It transfers a set of three glucose residues from a limit branch
and then cleaves the a(1 6) bond via hydrolysis.

It transfers a set of three glucose residues from a limit branch and
then cleaves the a(1 6) bond via hydrolysis.

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The compound uridine diphosphate glucose (UDPG) plays a role
in
A. glycogen breakdown.
B. glycogen synthesis.
C. glycolysis.
D. gluconeogenesis.

glycogen synthesis

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The activity of glycogen phosphorylase depends on
A. allosteric control
B. covalent modification
C. both of these
D. neither of these

both of these

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Glucose-6-phosphatase activity is found associated with the endoplasmic
reticulum
A. True
B. False

True

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How are the branches in glycogen produced?
A. A branching enzyme catalyses the addition of a single glucose
unit via an a(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 a(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 a(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 a(1,4) section of glycogen to make a new a(1,6)
branch point.

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

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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.

It adds a UMP molecule to glucose-1-phosphate by splitting out
pyrophosphate.

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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.

All of these events can occur when a single glucose residue is added.

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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

both of these

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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.

B. 2

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When glycogen synthase is phosphorylated
A. its activity decreases.
B. its activity increases.
C. its activity is unaffected.
D. That enzyme doesn’t get phosphorylated.

its activity decreases

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When glycogen phosphorylase is phosphorylated
A. its activity decreases.
B. its activity increases.
C. its activity is unaffected.
D. That enzyme doesn’t get phosphorylated.

its activity increases

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Where is the enzyme glucose-6-phosphatase located?
A. cytosol
B. mitochondria
C. endoplasmic reticulum
D. none of these

endoplasmic reticulum

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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

are not activated simultaneously

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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

are modified by the same enzymes

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

True

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.

Subunit association and dissociation

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

the phosphorylated R form

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

False

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

True

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

True

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.

It draws more water into the cells than glucose would.

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

False

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

True

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.

Glucose

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

False

Gluconeogenesis is the synthesis of A. glucose from non-carbohydrate precursors B. glycogen from glucose C. pyruvate from glucose D. fatty acids from glucose

glucose from non-carbohydrate precursors

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

all of these

Which enzyme is used in gluconeogenesis, but NOT in glycolysis? A. PEP carboxykinase B. enolase C. phosphohexose isomerase D. 3-phosphoglycerate dehydrogenase

PEP carboxykinase

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

requires biotin for activity

In which cellular compartment is pyruvate carboxylase found? A. cytosol B. mitochondria C. endoplasmic reticulum D. nucleus

mitochondria

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.

CO2 is incorporated into the glucose product

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

C. glucose-6-phosphatase, fructose-1,6-bisphosphatase, pyruvate carboxylase, and phosphoenolpyruvate carboxykinase

In gluconeogenesis, the initial reaction converts pyruvate to A. oxaloacetate B. acetyl-CoA C. phosphoenolpyruvate D. lactate

oxaloacetate

The first reaction of gluconeogenesis is A. an oxidative decarboxylation B. a carboxylation C. a redox reaction D. a phosphate transfer

a carboxylation

Which nucleotide triphosphate is hydrolysed in the conversion of oxaloacetate to phosphoenolpyruvate? A. ATP B. GTP C. CTP D. UTP E. No nucleotide triphosphate is hydrolysed.

GTP

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.

Malate dehydrogenase activity in the cytoplasm

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

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

How many ATP equivalents are expended to convert 2 pyruvates to 1 glucose? A. 2 B. 4 C. 6 D. 8

It is impossible to reverse any kinase reaction under physiological conditions. A. True B. False

True

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

True

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.

is catalyzed by the same protein dependant upon whether it is phosphorylated or not.

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.

stimulate glycolysis and inhibit gluconeogenesis

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.

inhibited by fructose 2,6-bisphosphate

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.

different enzymes, subject to independent control, are responsible for the synthesis and breakdown of the same substance.

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

is an important regulatory molecule in the control of carbohydrate metabolism

Which of the following is not true concerning control of pyruvate kinase? A. The phosphorylated form is less active B. It is inhibited by ATP C. It is activated by fructose 1,6-bisphosphate D. It is inhibited by low blood glucose levels E. All of these

All of these

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.

Ability to replenish the levels of glucose in the blood.

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.

your liver cells will be running gluconeogenesis and your leg muscle cells will be running glycolysis.

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.

glycolysis takes place in muscle and gluconeogenesis in the liver

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.

Situations where there are two different enzymes used to reverse a specific step in a metabolic pathway.

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.

Conversion of lactate produced in the muscle by regeneration of glucose in the liver.

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.

All of these are used to regulate metabolism.

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

B. False

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.

to synthesize NADPH and pentose phosphates

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.

It depends on whether the glucose goes through the oxidative part of the pathway or not.

What kind of enzyme catalyzes the following reaction? ribose-5-P « ribulose-5-P A. transketolase B. epimerase C. transaldolase D. isomerase

isomerase

What kind of enzyme catalyzes the reaction ribulose-5-P « xylulose- 5-P? A. transketolase B. epimerase C. transaldolase D. isomerase

epimerase

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.

The process reduces glucose-6-phosphate.

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

False

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.

produce NADPH rather than NADH.

The conversion of ribulose 5-phosphate to xylulose 5-phosphate is A. a dehydration B. an oxidation C. a reduction D. an epimerization

an epimerization

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

transfer of a three-carbon unit

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

glycerate-3-phosphate

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

True

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

it catalyzes an inversion of configuration at carbon-3

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.

All of these sizes are used in this pathway.

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.

Thiamine can transfer all of these types of groups.

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.

C5 + C5 C6 + C4

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

all of these

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