biochem ch12 Flashcards
Gluconeogenesis uses the same enzymatic reactions of glycolysis
except for the ________.
A) pyruvate kinase catalyzed step
B) 4 irreversible reactions in glycolysis
C) 3 irreversible reactions in glycolysis
D) 2 irreversible reactions in glycolysis
Glucose is stored as ________ in bacteria and animals.
Gluconeogenesis is the ________.
A) result of amylase activity
B) formation of glycogen
C) formation of starches
D) formation of glucose from simple two and three-carbon precursors
E) formation of glucose from other carbohydrates
Glucose monomers can be released to fuel energy by degradation of
A) stored glycogen.
D) A and B.
E) A, B and C
Gluconeogenesis generates ________.
A) 2 ATP and 2 NADH
B) 1 ATP and 1 NADH
C) 1 ATP and 0 NADH
D) 0 ATP and 0 NADH
The ________ is the site of most gluconeogenesis in mammals.
C) cytosol of all cells
D) small intestine
Which is evidence for gluconeogenesis being a more ancient metabolic
pathway than glycolysis?
A) The protein sequences for the gluconeogenesis enzymes are less conserved than those for glycolysis, indicating greater diversity developed by evolution.
B) Many archaebacterial enzymes for gluconeogenesis have the same catalytic triad as those in modern mammals.
C) Glycolysis in bacteria generally has fewer pathway steps, indicating that it has had less time to evolve.
D) Some bacterial species that diverged very early in prokaryotic evolution have gluconeogenesis, but not glycolysis.
The only known regulatory mechanism for pyruvate carboxylase
A) activation by acetyl CoA.
B) activation by phosphorylation.
C) activation by cAMP.
D) activation by NADH
Gluconeogenesis is regulated by
B) allosteric modulation.
C) concentration of its substrates.
D) All of the above.
An intermediate found in gluconeogenesis and not glycolysis
D) fructose 1,6-bisphosphate.
The activity of phosphoenolpyruvate carboxykinase (PEPCK) is most
A) glucagon concentration.
B) insulin concentration.
C) the level of PEPCK gene transcription.
D) the elevation of cAMP concentration on fasting
Gluconeogenesis shares some, but not all, enzymes with the glycolytic
pathway. It would appear to be more efficient if both pathways used
all of the same enzymes since the pathways are essentially the
reverses of each other. Why don't both pathways use all of the same
A) The reactions where enzymes differ occur in different parts of the cell for glycolysis versus gluconeogenesis.
B) Enzymes can catalyze a reaction only in one direction, so naturally the two pathways have some enzymes that differ.
C) In tissues where gluconeogenesis occurs, the glycolytic enzymes are present at extremely low concentrations.
D) Three of the reaction steps in gluconeogenesis would have prohibitively large, positive free energies if they used glycolytic enzymes for their catalysis.
In the Cori cycle, gluconeogenesis occurs in ________ and glycolysis
A) liver; muscle
B) liver; liver
C) muscle; muscle
D) muscle; liver
Any compound that can be converted to ________ can be a precursor for
D) All of the above
E) B or C
Which of the following is not a precursor for gluconeogenesis?
The sequence of glucose conversion to lactate in peripheral tissues,
delivery of lactate to the liver, formation of glucose from lactate in
the liver, and delivery of glucose back to peripheral tissues is known
as the ________.
A) glyoxylate cycle
B) Kreb's cycle
C) Cori cycle
D) gluconeogenesis cycle
In ruminants, microorganisms produce propionate. The three-carbon
acid must be converted to ________ before entering the gluconeogenesis
A) acetyl CoA
C) citric acid
D) succinyl CoA
During fasting, when glycogen supplies are depleted, ________ become
a major source of carbon for gluconeogenesis.
A) amino acids
B) nucleic acids
C) fatty acids
D) lactate and pyruvate
The reaction that converts amino acids into keto acids (such as
pyruvate) is called
A) the Cori cycle.
Glycerol is converted to ________ when it is used for
A) dihydroxyacetone phosphate
A substrate cycle in a metabolic pathway ________.
A) is a good point for regulation of the pathway
B) includes only diffusion-controlled reactions
C) allows for substrates to be passed to alternative pathways
D) is a point that starts a cascade effect
When ATP levels are high, glycolysis is (stimulated, reduced)
________, and when AMP levels are high gluconeogenesis is (stimulated,
A) stimulated; reduced
B) stimulated; stimulated
C) reduced; reduced
D) reduced; stimulated
The interconversion of which pair of substrates is used as a
regulatory point in gluconeogenesis?
A) Lactate and pyruvate.
B) Dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.
C) Fructose 1,6-bisphosphate and fructose 6-phosphate.
D) Phosphoenolpyruvate and 2-phosphoglycerate.
Fructose 2,6-bisphosphate ________ glycolysis while it ________
A) stimulates; stimulates
B) stimulates; inhibits
C) inhibits; stimulates
D) inhibits; inhibits
Which is an intermediate formed in the conversion of glucose to
D) Aldose reductase
Sorbitol does not accumulate when glucose is not elevated
A) there is not enough NADPH to form it.
B) aldose reductase has a high Km for glucose.
C) aldose reductase has a low Km for glucose.
D) fructose inhibits aldose reductase.
Which substance is not needed for the conversion of glucose to
B) Aldose reductase.
What types of reactions are involved in the two-step conversion of
glucose to fructose?
A) Reduction followed by oxidation.
B) Two sequential hydrolysis reactions.
C) Hydrolysis followed by isomerization (rearrangement).
D) Phosphorylation followed by dephosphorylation.
What is a cause of cataracts in the eye lens of individuals with
A) Accumulation of sorbitol and protein precipitation in the lens.
B) Precipitation of glucose not oxidized by glycolysis in the lens.
C) The absence of membrane transport proteins for pyruvate in the lens cells.
D) Lack of regulation of gluconeogenesis in the lens and the accumulation of fructose.
The pentose phosphate pathway has two primary products. They are
A) ATP and NADPH
B) oxaloacetate and acetyl CoA
C) sorbitol and fructose
D) ribose-5-phosphate and NADPH
Individuals with G6PDH deficiency have increased resistance to
malaria because the parasite does not survive well in cells
B) high levels of NADPH.
C) low levels of NADPH.
D) hexose 6-phosphate.
The non-oxidative stage of the pentose phosphate pathway ________.
A) produces NADPH and releases CO2
B) consists entirely of near-equilibrium reactions
C) contains two reactions whose enzymes are allosterically inhibited by NADPH
D) consumes four ATP molecules
The pentose phosphate pathway can alternatively be called the pentose
phosphate cycle because ________ is a net product of the pathway that
can be recycled.
A) glucose 6-phosphate
C) carbon dioxide
Deficiencies in G6PDH (glucose-6-phosphate dehydrogenase) in humans
A) varying degrees of hemolytic anemia.
B) increased resistance to malaria.
C) lack of NADPH in many cells.
D) All of the above.
E) A and B.
The major regulatory step of the pentose phosphate pathway is
catalyzed by which enzyme?
C) Glucose 6-phosphate dehydrogenase.
D) Ribose 5-phosphate isomerase.
The non-oxidative stage of the pentose phosphate pathway produces
substances that are intermediates of ________.
B) the citric acid cycle
C) the Cori cycle
Fragments containing three carbons can be transferred from a ketose
phosphate to an aldose phosphate by the enzyme ________.
A) pyruvate carboxylase
C) debranching enzyme
D) ribose-5-phosphate isomerase
What is the prosthetic group of transketolase?
A) Thiamine pyrophosphate.
C) Pyridoxal phosphate.
Which is not a function of the main products of the pentose phosphate
A) To maintain levels of NADPH.
B) To provide reducing power for the synthesis of fatty acids.
C) To serve as precursors in the biosynthesis of RNA and DNA.
D) To raise the concentration of cAMP
The activity of glycogen phosphorylase can be controlled by
C) glucose 6-phosphate.
D) protein subunit separation.
E) All of the above
Why does glycolysis produce more energy (more ATP) from glucose units
released by glycogen degradation than from free glucose?
A) Limit dextrin contains additional molecules.
B) The debranching enzyme releases free glucose.
C) The glucose is already phosphorylated after glycogen phosphorylase action.
D) The glucose from glycogen degradation bypasses glycolysis.
E) All of the above.
A) a protein for attachment of primer glucose chains.
B) an enzyme that attaches glucose residues to a growing chain.
C) a pre-existing primer in glycogen synthesis.
D) A and B
Glucose 1-phosphate formed by glycogen degradation is converted to
glucose 6-phosphate by phosphoglucomutase. Why is this
A) Glucose 6-phosphate is more stable.
B) Glucose 6-phosphate is converted to free glucose.
C) Glucose 6-phosphate is an intermediate in several pathways, including glycolysis.
D) Glucose 6-phosphate can be transported to the liver.
E) All of the above.
Glycogen synthesis in vertebrates requires ________ to activate
E) All of the above
Possible treatment for diabetes are inhibitors of glycogen
phosphorylase that mimic the natural inhibitory activity of ________
in non-diabetic persons.
C) cyclic AMP
What is the driving force for the reaction catalyzed by UDP-glucose
pyrophosphorylase that converts glucose 1-phosphate to
A) Its large negative free energy change.
B) The formation of an energy-rich product.
C) The subsequent hydrolysis of pyrophosphate.
D) The change in concentration of UTP.
Which statement is true about the reaction catalyzed by glycogen
A) It polymerizes free glucose to glycogen in the liver.
B) It requires UTP-glucose for chain lengthening.
C) It can both lengthen glycogen chains as well as form new branches.
D) It requires a primer of four to eight linked glucose residues
Glycogen degradation occurs in
C) muscle and liver.
E) brain cells
The enzyme for the key regulatory step in glycogen biosynthesis is
A) glycogen synthase.
C) branching enzyme.
E) UDP-glucose pyrophosphorylase
Glucagon is excreted when blood glucose is ________ (high, low),
while insulin is secreted when blood glucose is ________ (high, low).
A) high; high
B) high; low
C) low; low
D) low; high
Protein kinase A, which stimulates glycogen degradation, is activated
D) cyclic AMP.
E) adrenergic receptors.
Binding of epinephrine to a1-adrenergic receptors has what
A) Elevates the degradation rate of glycogen.
B) Activates protein kinase A.
C) Lowers the rate of glycogen synthesis.
D) Reduces the effects of insulin.
E) All of the above
Glycogen phosphorylase is ________ (more, less) active when
phosphorylated, and it is ________ (activated, inhibited) by glucose
A) more; activated
B) less; activated
C) more; inhibited
D) less; inhibited
Phosphorylation can be used to either inactivate or activate enzymes.
This is a key element in the regulation of glucose metabolism.
Phosphorylation of glycogen phosphorylase ________ it; phosphorylation
of glycogen synthase ________ it.
A) activates; activates
B) activates; inactivates
C) inactivates; inactivates
D) inactivates; activates
In addition to control of activity by phosphorylation, phosphorylase
kinase is activated by
The sequence of enzymes active in liver to degrade glycogen in
response to glucagon is: ________. (~P indicates phosphorylation)
A) Protein kinase A, phosphorylase kinase~P, glycogen phosphorylase a~P
B) protein kinase A, glycogen phosphorylase a~P, phosphorylase kinase~P
C) phosphorylase kinase, glycogen phosphorylase b, protein kinase A
D) phosphorylase kinase, glycogen phosphorylase b, protein kinase A, glucagon
Unlike liver tissue, muscle and some other tissues differ in
regulation of glycogen metabolism because
A) the enzymes are different.
B) there is no effect of glucagon.
C) there is no effect of insulin.
D) inhibitor-1 controls protein phosphatase-1.
E) there is no role for cyclic AMP.
Which is true about glycogen phosphorylase in liver and
A) They are identical and activated in the same way.
B) In liver glucose is an inhibitor; glucose is not an inhibitor in muscle.
C) The liver enzyme is activated by phosphorylation, but the muscle version is activated by proteolytic cleavage.
D) Glycogen phosphorylase is found only in liver, there is none in muscle tissue
Glycogen phosphorylase was the first enzyme shown to be regulated by
A) covalent modification
B) proteolytic cleavage
C) a cascade reaction
D) feedback inhibition
Which statement is false about glucagon?
A) It forms a protein scaffold for glycogen.
B) It is a hormone that contains 29 amino acids.
C) Elevated levels are associated with a fasting state.
D) It is produced in the pancreas
During fasting, what role does gluconeogenesis play?
A) Aids in the release of glucose from stored glycogen in the liver.
B) Uses alanine to restore blood glucose levels.
C) Produces products that slow the oxidation of pyruvate.
D) Helps transport glucose across the blood-brain barrier to maintain brain glucose levels
Which is a reasonable concentration for glucose in the blood?
A) 5 μM
B) 5 mM
C) 50 mM
D) 5 M
Under starvation conditions, about how long does it take in humans
for the body to deplete the glycogen store in the liver?
A) 10 minutes
B) 4 hours
C) 24 hours
D) 1 week
In which order are the following energy sources (either directly or
through gluconeogenesis) depleted during starvation?
A) Dietary; adipose tissue; proteins; liver glycogen.
B) Adipose tissue; dietary; liver glycogen; proteins.
C) Dietary; liver glycogen; adipose tissue; proteins.
D) Liver glycogen; dietary; adipose tissue; proteins