Deck 12: Gluconeogenesis, the Pentose Phosphate Pathway, and Glycogen Metabolism

Question 1

Which substance is not needed for the conversion of glucose to fructose?

A) NADPH
B) Aldose reductase
C) QH₂
D) NAD⁺

Answer 1

QH₂

Question 2

In ruminants, microorganisms produce propionate. The three-carbon acid must be converted to before entering the gluconeogenesis pathway.

A) acetyl CoA
B) lactate
C) citric acid
D) succincyl CoA

Answer 2

succincyl CoA

Question 3

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

Answer 3

3 irreversible reactions in glycolysis

Question 4

Which is an intermediate formed in the conversion of glucose to fructose?

A) glucose-1-phosphate
B) sorbitol
C) ribose
D) aldose reductase

Question 5

Which of the following is not a precursor for gluconeogenesis?

A) alanine
B) glycerol
C) oxaloacetate
D) acetate
E) ethanol

Question 6

Glucose that is not part of a diet may be provided by degradation of

A) stored glycogen.
B) starch.
C) dextrin.
D) A and B
E) A, B and C

Question 7

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

Question 8

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

Question 9

The reaction that converts amino acids into keto acids such as pyruvate) is called

A) the Cori cycle.
B) catabolism.
C) transamination.
D) dehydrogenation.

Question 10

Glycerol is converted to when it is used for gluconeogenesis.

A) dihydroxyacetone phosphate
B) phosphoenolpyruvate
C) oxaloacetate
D) 3-phosphoglycerate

Question 11

The is the site of most gluconeogenesis in mammals.

A) liver
B) pancreas
C) cytosol of all cells
D) small intestine

Question 12

An intermediate found in gluconeogenesis and not glycolysis is

A) 2-phosphoglycerate.
B) oxaloacetate.
C) phosphoenolpyruvate.
D) fructose 1,6-bisphosphate.

Question 13

Glucose is stored as in bacteria and animals.

A) glucagons
B) starch
C) glycogen
D) NADPH

Question 14

The activity of phosphoenolpyruvate carboxykinase PEPCK) is most affected by

A) glucagon concentration.
B) insulin concentration.
C) the level of PEPCK gene transcription.
D) the elevation of cAMP concentration on fasting.

Question 15

The sequence of glucose oxidation 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) Krebʹs cycle
C) Cori cycle
D) gluconeogenesis cycle

Question 16

Fructose 2,6-bisphosphate glycolysis while it gluconeogenesis.

A) stimulates; stimulates
B) stimulates; inhibits
C) inhibits; stimulates
D) inhibits; inhibits

Question 17

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 donʹt both pathways use all of the same enzymes?

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.

Question 18

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

Question 19

In the Cori cycle, gluconeogenesis occurs in and glycolysis in .

A) liver; muscle
B) liver; liver
C) muscle; muscle
D) muscle; liver

Question 20

Any compound that can be converted to can be a precursor for gluconeogenesis.

A) citrate
B) pyruvate
C) oxaloacetate
D) All of the above
E) B or C

Question 21

Which statement is true about the reaction catalyzed by glycogen synthase?

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.

Question 22

Fragments containing three carbons can be transferred from a ketose phosphate to an aldose phosphate by the enzyme .

A) pyruvate carboxylase
B) transaldolase
C) debranching enzyme
D) ribose-5-phosphate isomerase

Question 23

Glycogen degradation occurs in

A) muscle.
B) liver.
C) muscle and liver.
D) saliva.
E) brain cells.

Question 24

What is the prosthetic group of transketolase?

A) thiamine pyrophosphate
B) biotin
C) pyridoxal phosphate
D) NAD⁺

Question 25

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

Question 26

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

Question 27

Deficiencies in G6PDH glucose-6-phosphate dehydrogenase) in humans causes

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

Question 28

What is a cause of cataracts in the eye lens of individuals with diabetes?

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.

Question 29

The enzyme for the key regulatory step in glycogen biosynthesis is

A) glycogen synthase.
B) glycogenin.
C) branching enzyme.
D) phosphoglucomutase.
E) UDP-glucose pyrophosphorylase.

Question 30

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

Question 31

The non-oxidative stage of the pentose phosphate pathway produces substances that are intermediates of .

A) glycolysis
B) the citric acid cycle
C) the Cori cycle
D) glycogenolysis

Question 32

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

Question 33

The major regulatory step of the pentose phosphate pathway is catalyzed by which enzyme?

A) transaldolase
B) phosphofructokinase-1
C) glucose 6-phosphate dehydrogenase
D) ribose 5-phosphate isomerase

Question 34

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

Question 35

Glucose 1-phosphate formed by glycogen degradation is converted to glucose 6-phosphate by phosphoglucomutase. Why is this beneficial?

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

Question 36

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
B) NADP⁺
C) carbon dioxide
D) phosphate
E) UDP

Question 37

What is the driving force for the reaction catalyzed by UDP-glucose pyrophosphorylase that converts glucose 1-phosphate to UDP-glucose?

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

Question 38

The activity of glycogen phosphorylase can be controlled by

A) phosphorylation.
B) ATP.
C) glucose 6-phosphate.
D) protein subunit separation.
E) All of the above

Question 39

Glycogen synthesis in vertebrates requires to activate glucose 1-phosphate.

A) ATP
B) ADP
C) UTP
D) UDP
E) All of the above

Question 40

Which is not a function of the main products of the pentose phosphate pathway?

A) To maintain the reduced form of iron in hemoglobin.
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.

Question 41

Glycerol can supply electrons to the electron transport chain at the same time as it can be a precursor in gluconeogenesis.

Question 42

Phosphorylation can be used to either inactive 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

Question 43

All blood glucose in humans is derived from carbohydrate sources included in the diet.

Question 44

Binding of epinephrine to a₁-adrenergic receptors has what effect?

A) elevates the degradation rate of glycogen
B) activates protein kineses A
C) lowers the rate of glycogen synthesis
D) reduces the effects of insulin
E) All of the above

Question 45

All species can make glucose from two-carbon or three-carbon precursors.

Question 46

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.

Question 47

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.

Question 48

In addition to control of activity by phosphorylation, phosphorylase kinase is activated by

A) Calmodulin.
B) Ca²⁺.
C) cAMP.
D) Inhibitor-1.

Question 49

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.

Question 50

Fructose 2,6-bisphosphate is a modulator that can stimulate either glycolysis or gluconeogenesis, depending on cellular glucose concentrations.

Question 51

More energy in the form of ATP is required to synthesize glucose than can be obtained from it by glycolysis alone.

Question 52

Glucagon increases the transcription of the gene for phosphoenolpyruvate carboxykinase (PEPCK) in gluconeogenesis, while insulin decreases it.

Question 53

At high glucagon concentrations gluconeogenesis will be favored over glycolysis.

Question 54

Protein kinase A, which stimulates glycogen degradation, is activated directly by

A) glucagon.
B) insulin.
C) epinephrine.
D) cyclic AMP.
E) adrenergic receptors.

Question 55

Ruminants, like cows, can utilize propionate as a precursor for gluconeogenesis.

Question 56

The sequence of enzymes active in liver to degrade glycogen in response to glucagon is: . ~P indicates phosphorylation)

A) phosphorylase kinase, glycogen phosphorylase b, protein kinase A, glucagon
B) glucagon, phosphorylase kinase, glycogen phosphorylase b, protein kinase A
C) glucagon, Protein kinase A, phosphorylase kinase~P, glycogen phosphorylase a~P
D) glucagon, protein kinase A, glycogen phosphorylase a~P, phosphorylase kinase~P

Question 57

Which is a reasonable concentration for glucose in the blood?

A) 5 μM
B) 5 mM
C) 50 mM
D) 5 M

Question 58

The reaction catalyzed by polyol dehydrogenase involves the reduction of sorbitol.

Question 59

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

Question 60

Glycogen phosphorylase is more, less) active when phosphorylated, and it is activated, inhibited) by glucose 6-phosphate.

A) more; activated
B) less; activated
C) more; inhibited
D) less; inhibited

Question 61

Glycogen phosphorylaseacts on the non-reducing ends of glycogen.

Question 62

Glycogen storage disease results in glycogen accumulation in the liver and kidneys. It can be controlled by changing the diet.

Question 63

Glycogenin is a protein scaffold for glycogen as well as an enzyme catalyzing extension of the glycogen primer.

Question 64

UDP-glucose is a precursor of glycogen in all cells.

Question 65

The brain normally uses both glucose and fatty acids as energy sources.

Question 66

Under fasting conditions the liver increases its rate of gluconeogenesis to maintain blood glucose levels, but this can only be maintained for a few days before the rate decreases.

Question 67

Two molecules of NADPH are generated for each molecule of glucose 6-phosphate that enters the pentose phosphate pathway.

Question 68

Rapidly dividing cells generally have a high pentose phosphate pathway activity.

Question 69

There are no branched polysaccharide chains in limit dextrin.

Question 70

The enzymes transketolase and transaldolase of the pentose phosphate pathway are each very specific for only one substrate.

Question 71

The enzyme transketolase transfers 2-carbon units from ketose phosphates to aldose phosphates.

Question 72

Since caffeine inhibits cAMP phosphodiesterase, too much coffee can result in the synthesis of too much glycogen.

Question 73

Glucose 1,6-bisphosphate is the primary starting substrate for the pentose phosphate pathway.

Question 74

Epinephrine can stimulate glycogen degradation while at the same time, lowering glycogen synthesis.

Question 75

Enzymes to regulate glycogen metabolism are always active when phosphorylated by protein kinases.