Glycogen Homework problems Flashcards
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.
e) a and b are both correct.
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
c) UDP-glucose
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
d) phosphorylase; synthase
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
b) Activation, conversion from glycogen phosphorylase B to glycogen phosphorylase A
The process of glycogenolysis is an example of __________.
a) Hydrolysis
b) Thiolysis
c) Lysis
d) Phosphorolysis
e) Phosphorylation
e) Phosphorylation
d) Phosphorolysis
- 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.
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
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
a) alpha-1,4/alpha-1,6
The formation of primers to initiate glycogen synthesis is carried out by ___.
a) Glycogenin
b) Insulin
c) Glucagon
d) UDP-glucose
a) Glycogenin
This hormone leads to glycogen synthesis.
a) Insulin
b) Glucagon
c) Epinephrine
d) Cortisol
a) Insulin
Phosphorylase b is converted to phosphorylase a by ____.
a) Phosphorylase Kinase
b) cAMP
c) GTP
d) Hormone-sensitive lipase
a) Phosphorylase Kinase
The active form of glycogen synthase is ___.
a) Dephosphorylated
b) Phosphorylated
c) Glycosylated
d) Ribosylated
a) Dephosphorylated
- The enzyme which removes the glucose residue at branch points of glycogen during glycogen
breakdown is ____.
a) Debranching enzyme
b) Branching enzyme
c) Transerase
a) Debranching enzyme
When protein phosphatase 1 is active,
a.) glycogen synthesis predominates
b.) glycogen breakdown predominates
c.) neither
d.) both
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
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
a) Epinephrine and Glucagon
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
a) Protein Phosphatase 1
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
b) Glycogen is a polymer of beta-D-Glucose
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
c) Glucose-6-phosphatase
Glycogen phosphorylase is responsible for the breakdown of glycogen to
a) Glucose
b) Glucose-6-phosphate
c) Glucose-1-phosphate
d) Maltose
c) Glucose-1-phosphate
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
c) Glycogen phosphorylase possess high-affinity binding to glycogen in T conformational state
Which of the following metabolite allosterically activate glycogen phosphorylase?
a) ATP
b) AMP
b) Glucose-6-P
d) Glucose-1-P
b) AMP
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
b) Phosphorylase kinase
Which of the following is not the direct/ indirect activator of glycogen phosphorylase in muscle?
a) AMP
b) Ca++
c) Epinephrine
d) Insulin
d) Insulin
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
a) Glycogen synthase is activated in the phosphorylated state.
