Glycogen Homework problems

Question 1

Glycogen Metabolism Practice Problems and Answers

The breakdown of glycogen to form glucose occurs

a) in the liver by phosphorolysis.
b) in the muscles by phosphorolysis.
c) in the liver by hydrolysis.
d) in the muscles by hydrolysis.
e) a and b are both correct.

Answer 1

e) a and b are both correct.

Question 2

The precursor to glycogen in the glycogen synthase reaction is
a) glucose-1-P.
b) glucose-6-P.
c) UDP-glucose.
d) UTP-glucose.
e) None of the abov

Answer 2

c) UDP-glucose

Question 3

The active form of glycogen ___ is phosphorylated; the active form of glycogen ___ is
dephosphorylated.
a) hydrolase; dehydrogenase
b) dehydrogenase; hydrolase
c) hydrolase; semisynthase
d) phosphorylase; synthase
e) synthase; phosphorylas

Answer 3

d) phosphorylase; synthase

Question 4

Phosphorylation of glycogen phosphorylase has what effect on the enzyme?
a) Phosphorylation has no effect
b) Activation, conversion from glycogen phosphorylase B to glycogen phosphorylase A
c) Inactivation, conversion from glycogen phosphorylase B to glycogen phosphorylase A
d) Phosphorylation only confers partial activation
e) Activation, conversion from glycogen phosphorylase A to glycogen phosphorylase B

Answer 4

b) Activation, conversion from glycogen phosphorylase B to glycogen phosphorylase A

Question 5

The process of glycogenolysis is an example of __________.

a) Hydrolysis
b) Thiolysis
c) Lysis
d) Phosphorolysis
e) Phosphorylation
e) Phosphorylation

Answer 5

d) Phosphorolysis

Question 6

6. Which of the following statements about glycogen phosphorylase (GP) is incorrect?
   a) AMP is an inhibitor of glycogen phosphorylase.
   b) This enzyme is active during times of starvation.
   c) The dephosphorylated form of glycogen phosphorylase is less active.
   d) Glucose-6-phosphate is a negative regulator of glycogen phosphorylase.
   e) Glucose is a competitive inhibitor of glycogen phosphorylase.

Answer 6

a) AMP is an inhibitor of glycogen phosphorylase.

AMP is an activator of GP, whereas ATP is an inhibitor of GP. GP cleaves the alpha 1-4 glycosidic bond between a terminal glucose molecule and the rest of the glycogen straight chain, yielding glucose-1- phosphate during glycogenolysis

Question 7

In glycogen, the chains are formed by ____ glycosidic linkages while the branches are ____ glycosidic
linkages.

a) alpha-1,4/alpha-1,6
b) alpha-1,6/ alpha-1,4

Answer 7

a) alpha-1,4/alpha-1,6

Question 8

The formation of primers to initiate glycogen synthesis is carried out by ___.

a) Glycogenin
b) Insulin
c) Glucagon
d) UDP-glucose

Answer 8

a) Glycogenin

Question 9

This hormone leads to glycogen synthesis.
a) Insulin
b) Glucagon
c) Epinephrine
d) Cortisol

Answer 9

a) Insulin

Question 10

Phosphorylase b is converted to phosphorylase a by ____.
a) Phosphorylase Kinase
b) cAMP
c) GTP
d) Hormone-sensitive lipase

Answer 10

a) Phosphorylase Kinase

Question 11

The active form of glycogen synthase is ___.

a) Dephosphorylated
b) Phosphorylated
c) Glycosylated
d) Ribosylated

Answer 11

a) Dephosphorylated

Question 12

12. The enzyme which removes the glucose residue at branch points of glycogen during glycogen
    breakdown is ____.

a) Debranching enzyme
b) Branching enzyme
c) Transerase

Answer 12

a) Debranching enzyme

Question 13

When protein phosphatase 1 is active,

a.) glycogen synthesis predominates
b.) glycogen breakdown predominates
c.) neither
d.) both

Answer 13

a.) glycogen synthesis predominates

Glycogen synthesis predominates.
This is because PP1 dephosphorylates phosphorylase a converting it to the inactive form phosphorylase b, resulting in no degradation

Question 14

The two hormones that signal for glycogen breakdown are ____ and ____.
a) Epinephrine and Glucagon
b) Glucagon and insulin
c) Insulin and epinephrine
d) Cortisol and cholesterol

Answer 14

a) Epinephrine and Glucagon

Question 15

The enzyme that removes the phosphate from glycogen synthase, converting it to the active a form
is ____.

a) Protein Phosphatase 1
b) Protein kinase
c) EcoRI
d) Synthase kinase

Answer 15

a) Protein Phosphatase 1

Question 16

Which of the following is false about glycogen molecules?

a) Glycogen is polysaccharide
b) Glycogen is a polymer of beta-D-Glucose
c) Glycogen consists of α(1-4) and α (1-6) glycosidic linkage
d) Glycogen is a helical structure with branching

Answer 16

b) Glycogen is a polymer of beta-D-Glucose

Question 17

Liver glycogen contributes to the maintenance of glucose but not muscle glycogen. Which of the following enzyme is absent in muscle?

a) Glycogen phosphorylase
b) Hexokinase
c) Glucose-6-phosphatase
d) Debranching enzyme

Answer 17

c) Glucose-6-phosphatase

Question 18

Glycogen phosphorylase is responsible for the breakdown of glycogen to

a) Glucose
b) Glucose-6-phosphate
c) Glucose-1-phosphate
d) Maltose

Answer 18

c) Glucose-1-phosphate

Question 19

Which of the following is false about enzyme glycogen phosphorylase of glycogen breakdown?

a) Glycogen phosphorylase is active as a homodimer.
b) Glycogen phosphorylase is present in two conformation state
c) Glycogen phosphorylase possess high-affinity binding to glycogen in T conformational state
d) Glycogen phosphorylase high-affinity binding to glycogen in R conformation state

Answer 19

c) Glycogen phosphorylase possess high-affinity binding to glycogen in T conformational state

Question 20

Which of the following metabolite allosterically activate glycogen phosphorylase?

a) ATP
b) AMP
b) Glucose-6-P
d) Glucose-1-P

Answer 20

b) AMP

Question 21

n response to glucagon and epinephrine, cells undergo a series of changes in signal-transducing molecules that phosphorylates and activates glycogen phosphorylase. Which of the following enzyme is responsible for covalent modification of glycogen phosphorylase?

a) Protein kinase A
b) Phosphorylase kinase
c) Protein kinase C
d) Protein kinase B

Answer 21

b) Phosphorylase kinase

Question 22

Which of the following is not the direct/ indirect activator of glycogen phosphorylase in muscle?

a) AMP
b) Ca++
c) Epinephrine
d) Insulin

Answer 22

d) Insulin

Question 23

Which of the following statement is false regarding glycogenesis?

a) Glycogen synthase is activated in the phosphorylated state.
b) Glycogen synthase enzyme is inhibited by glucagon and epinephrine action.
c) Protein phosphatase removes the phosphate group and activates the enzyme
d) Insulin promotes glycogen synthesis in liver and skeletal muscles

Answer 23

a) Glycogen synthase is activated in the phosphorylated state.