Storage Mechanism and Control Flashcards
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.
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
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
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
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
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
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
What kind of reaction is used to release glucose units from glycogen?
A. hydrolysis
B. phosphorolysis
C. dehydration
D. oxidation
phosphorolysis
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
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
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.
The compound uridine diphosphate glucose (UDPG) plays a role
in
A. glycogen breakdown.
B. glycogen synthesis.
C. glycolysis.
D. gluconeogenesis.
glycogen synthesis
The activity of glycogen phosphorylase depends on
A. allosteric control
B. covalent modification
C. both of these
D. neither of these
both of these
Glucose-6-phosphatase activity is found associated with the endoplasmic
reticulum
A. True
B. False
True
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.
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.
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.
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
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
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
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
Where is the enzyme glucose-6-phosphatase located?
A. cytosol
B. mitochondria
C. endoplasmic reticulum
D. none of these
endoplasmic reticulum
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
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
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
6
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
