MCQ Principles of Metabolic Regulation

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) degradationof(α1→4)linkagesinglycogen
B) formation of (α1 → 4) linkages in glycogen.
C) formation of (α1 → 6) linkages during glycogen synthesis.
D) glycogendegradationintreebranches.
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) catalyzestheconversionofstarchintoglycogen.
B) is the enzyme responsible for forming branches in glycogen.
C) is the gene that encodes glycogen synthase.
D) istheprimeronwhichnewglycogenchainsareinitiated.
E) regulates the synthesis of glycogen.

Answer 3

D) istheprimeronwhichnewglycogenchainsareinitiated.

Question 4

Which of the following is true of glycogen synthase?
A) Activationoftheenzymeinvolvesaphosphorylation.
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) Theconversionofanactivetoaninactiveformoftheenzymeiscontrolledbytheconcentration
of cAMP.
E) The enzyme has measurable activity only in liver.

Answer 4

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) Itisespeciallypredominantinliverandmuscle.
B) The donor molecule is a sugar nucleotide.
C) The phosphorylated form of this enzyme is inactive.
D) Thisenzymeaddsglucoseunitstothenonreducingendofglycogenbranches.
E) This enzyme adds the initial glucose unit to a tyrosine residue in glycogenin.

Answer 5

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

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) keepingitsglucoselevelshigh.
B) maintaining a constant supply and concentration of ATP.
C) preserving its ability to carry out oxidative phosphorylation.
D) protectingitsenzymesfromrapiddegradation.
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) thereactionwillbeatequilibrium.
B) the reaction will go backward and be endergonic.
C) the reaction will go backward and be exergonic.
D) thereactionwillgoforwardandbeendergonic.
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) Activationbycleavageofaninactivezymogen
B) Allosteric response to a regulatory molecule
C) Alteration of the synthesis or degradation rate of an enzyme
D) Covalentmodificationoftheenzyme
E) Interactions between catalytic and regulatory subunits

Answer 9

A) Activationbycleavageofaninactivezymogen

Question 10

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

Answer 10

D) 1,3,4

Question 11

Cellular isozymes of pyruvate kinase are allosterically inhibited by:
A) highconcentrationsofAMP.
B) high concentrations of ATP.
C) high concentrations of citrate.
D) lowconcentrationsofacetyl-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) Ariseinthecellularleveloffructose-2,6-bisphosphatestimulatestherateofgluconeogenesis.
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) Theconversionofglucose6-phosphatetoglucoseiscatalyzedbyhexokinase,thesameenzyme
involved in glycolysis.
E) The conversion of phosphoenol pyruvate to 2-phosphoglycerate occurs in two steps, including a
carboxylation.

Answer 12

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

Answer 13

D) Thephosphofructokinase-1reactionisendergonic.

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

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

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) Bindingofglucose-6-phosphate
B) Dephosphorylation of multiple residues by phosphoprotein phosphorylase-1 (PP1)
C) Phosphorylation of specific residues by casein kinase II (CKII)
D) Phosphorylationofspecificresiduesbyglycogensynthasekinase-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) PP1canbephosphorylatedbyproteinkinaseA(PKA).
B) PP1 can dephosphorylate glycogen phosphorylase, glycogen synthase, and phosphorylase kinase.
C) PP1 is allosterically activated by glucose-6-phosphate.
D) PP1isinhibitedbyactivatedglycogenphosphorylase
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) theconcentrationoftheenzymeitself.
B) the concentration of other enzymes in the pathway.
C) the levels of regulatory molecules.
D) theamountsofsubstratemoleculespresentateachstep.
E) all of the above.

Answer 19

E) all of the above.