Chapter 15

Question 1

Glycogen is converted to monosaccharide units by:

A) glucokinase.
B) glucose-6-phosphatase
C) glycogen phosphorylase.
D) glycogen synthase.
E) glycogenase

Answer 1

C) glycogen phosphorylase.

Question 2

The glycogen-branching enzyme catalyzes:

A) degradation of (α1 → 4) linkages in glycogen
B) formation of (α1 → 4) linkages in glycogen.
C) formation of (α1 → 6) linkages during glycogen synthesis.
D) glycogen degradation in tree branches.
E) removal of unneeded glucose residues at the ends of branches.

Answer 2

C) formation of (α1 → 6) linkages during glycogen synthesis.

Question 3

Glycogenin:

A) catalyzes the conversion of starch into glycogen.
B) is the enzyme responsible for forming branches in glycogen.
C) is the gene that encodes glycogen synthase.
D) is the primer on which new glycogen chains are initiated.
E) regulates the synthesis of glycogen.

Answer 3

D) is the primer on which new glycogen chains are initiated.

Question 4

Which of the following is true of glycogen synthase?

A) Activation of the enzyme involves a phosphorylation.
B) It catalyzes addition of glucose residues to the nonreducing end of a glycogen chain by formation
of (α1 → 4) bonds.
C) It uses glucose-6-phosphate as donor of glucose units
D) The conversion of an active to an inactive form of the enzyme is controlled by the concentration
of cAMP.
E) The enzyme has measurable activity only in liver.

Answer 4

B) It catalyzes addition of glucose residues to the nonreducing end of a glycogen chain by formation
of (α1 → 4) bonds.

Question 5

Which one of the following statements abour mammalian glycogen synthase is not correct?
A) It is especially predominant in liver and muscle.
B) The donor molecule is a sugar nucleotide.
C) The phosphorylated form of this enzyme is inactive.
D) This enzyme adds glucose units to the nonreducing end of glycogen branches.
E) This enzyme adds the initial glucose unit to a tyrosine residue in glycogenin

Answer 5

E) This enzyme adds the initial glucose unit to a tyrosine residue in glycogenin

Question 6

The enzyme glycogen phosphorylase:

A) catalyzes a cleavage of β (1 → 4) bonds.
B) catalyzes a hydrolytic cleavage of (α1 → 4) bonds.
C) is a substrate for a kinase.
D) uses glucose 6-phosphate as a substrate.
E) uses glucose as a substrate

Answer 6

B) catalyzes a hydrolytic cleavage of (α1 → 4) bonds.

Question 7

Aside from maintaining the integrity of its hereditary material, the most important general metabolic
concern of a cell is:

A) keeping its glucose levels high.
B) maintaining a constant supply and concentration of ATP.
C) preserving its ability to carry out oxidative phosphorylation.
D) protecting its enzymes from rapid degradation.
E) running all its major metabolic pathways at maximum efficiency

Answer 7

B) maintaining a constant supply and concentration of ATP.

Question 8

If the mass action ratio, Q, for a reaction under cellular conditions is larger than the equilibrium
constant, Keq, then:

A) the reaction will be at equilibrium.
B) the reaction will go backward and be endergonic.
C) the reaction will go backward and be exergonic.
D) the reaction will go forward and be endergonic.
E) the reaction will go forward and be exergonic.

Answer 8

C) the reaction will go backward and be exergonic.

Question 9

Which one of the following types of mechanisms is not known to play a role in the reversible
alteration of enzyme activity?

A) Activation by cleavage of an inactive zymogen
B) Allosteric response to a regulatory molecule
C) Alteration of the synthesis or degradation rate of an enzyme
D) Covalent modification of the enzyme
E) Interactions between catalytic and regulatory subunits

Answer 9

A) Activation by cleavage of an inactive zymogen

Question 10

Gluconeogenesis must use “bypass reactions” to circumvent three reactions in the glycolytic pathway
that are highly exergonic and essentially irreversible. Reactions carried out by which three of the
enzymes listed must be bypassed in the gluconeogenic pathway?

1) Hexokinase
2) Phosphoglycerate kinase
3) Phosphofructokinase-1
4) Pyruvate kinase
5) Triosephosphate isomerase

A) 1, 2, 3
B) 1, 2, 4
C) 1, 4, 5
D) 1, 3, 4
E) 2, 3, 4

Answer 10

D) 1, 3, 4

Question 11

Cellular isozymes of pyruvate kinase are allosterically inhibited by:

A) high concentrations of AMP.
B) high concentrations of ATP.
C) high concentrations of citrate.
D) low concentrations of acetyl-CoA.
E) low concentrations of ATP.

Answer 11

B) high concentrations of ATP.

Question 12

Which of the following statements about gluconeogenesis in animal cells is true?

A) A rise in the cellular level of fructose-2,6-bisphosphate stimulates the rate of gluconeogenesis.
B) An animal fed a large excess of fat in the diet will convert any fat not needed for energy
production into glycogen to be stored for later use.
C) The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate is not catalyzed by
phosphofructokinase-1, the enzyme involved in glycolysis.
D) The conversion of glucose 6-phosphate to glucose is catalyzed by hexokinase, the same enzyme
involved in glycolysis.
E) The conversion of phosphoenol pyruvate to 2-phosphoglycerate occurs in two steps, including a
carboxylation.

Answer 12

C) The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate is not catalyzed by
phosphofructokinase-1, the enzyme involved in glycolysis.

Question 13

There is reciprocal regulation of glycolytic and gluconeogenic reactions interconverting fructose-6-
phosphate and fructose-1,6-bisphosphate. Which one of the following statements about this
regulation is not correct?

A) Fructose-2,6-bisphosphate activates phosphofructokinase-1.
B) Fructose-2,6-bisphosphate inhibits fructose-1,6-bisphosphatase.
C) The fructose-1,6-bisphosphatase reaction is exergonic.
D) The phosphofructokinase-1 reaction is endergonic.
E) This regulation allows control of the direction of net metabolite flow through the pathway

Answer 13

D) The phosphofructokinase-1 reaction is endergonic.

Question 14

Which of the following statements is true of muscle glycogen phosphorylase?

A) It catalyzes phosphorolysis of the (α1 → 6) bonds at the branch points of glycogen.
B) It catalyzes the degradation of glycogen by hydrolysis of glycosidic bonds.
C) It degrades glycogen to form glucose 6-phosphate.
D) It exists in an active (a) form and an inactive (b) form that is allosterically regulated by AMP.
E) It removes glucose residues from the reducing ends of the glycogen chains.

Answer 14

D) It exists in an active (a) form and an inactive (b) form that is allosterically regulated by AMP

Question 15

Which of the following is true of glycogen synthesis and breakdown?

A) Phosphorylation activates the enzyme responsible for breakdown, and inactivates the synthetic
enzyme.
B) Synthesis is catalyzed by the same enzyme that catalyzes breakdown.
C) The glycogen molecule “grows” at its reducing end.
D) The immediate product of glycogen breakdown is free glucose.
E) Under normal circumstances, glycogen synthesis and glycogen breakdown occur simultaneously
and at high rates.

Answer 15

A) Phosphorylation activates the enzyme responsible for breakdown, and inactivates the synthetic
enzyme.

Question 16

Glycogen phosphorylase a can be inhibited at an allosteric site by:

A) AMP.
B) calcium.
C) GDP.
D) glucagon.
E) glucose.

Answer 16

E) glucose.

Question 17

Which one of the following directly results in the activation of glycogen synthase?

A) Binding of glucose-6-phosphate
B) Dephosphorylation of multiple residues by phosphoprotein phosphorylase-1 (PP1)
C) Phosphorylation of specific residues by casein kinase II (CKII)
D) Phosphorylation of specific residues by glycogen synthase kinase-3 (GSK-3)
E) The presence of insulin

Answer 17

B) Dephosphorylation of multiple residues by phosphoprotein phosphorylase-1 (PP1)

Question 18

Which one of the following is not a characteristic of phosphoprotein phosphorylase-1 (PP1)?

A) PP1 can be phosphorylated by protein kinase A (PKA).
B) PP1 can dephosphorylate glycogen phosphorylase, glycogen synthase, and phosphorylase kinase.
C) PP1 is allosterically activated by glucose-6-phosphate.
D) PP1 is inhibited by activated glycogen phosphorylase
E) PP1 is phosphorylated by glycogen synthase kinase-3 (GSK3).

Answer 18

E) PP1 is phosphorylated by glycogen synthase kinase-3 (GSK3).

Question 19

The flux control coefficient for an enzyme in a multistep pathway depends on:

A) the concentration of the enzyme itself.
B) the concentration of other enzymes in the pathway.
C) the levels of regulatory molecules.
D) the amounts of substrate molecules present at each step.
E) all of the above

Answer 19

E) all of the above

Question 20

The elasticity coefficient for an enzyme in a multistep pathway depends on:

A) the concentration of the enzyme itself.
B) the levels of regulatory molecules.
C) the amounts of substrate molecules present at each step.
D) both the concentration of the enzyme itself and the amounts of substrate molecules present at each step..
E) both the levels of regulatory molecules. and the amounts of substrate molecules present at each step..

Answer 20

E) both the levels of regulatory molecules. and the amounts of substrate molecules present at each step..