Chapter 25 Glycogen Synthesis
Matching Questions
Use the following to answer questions 1-10:
Choose the correct answer from the list below. Not all of the answers will be used.
a) UDP-glucose
b) non-reducing
c) synthesis
d) glucose
e) glycogenin
f) von Gierke disease
g) glycogen synthase
h) UTP-glucose
i) protein phosphatase 1 (PP1)
j) PPi
k) glycogen phosphate
l) McArdle disease
1.
Synthesis of glycogen starts with the phosphate group transfer from UTP to ____________.
2.
____________ This is the activated form of glucose that is required for glycogen synthesis.
Ans: a
Section: 25.1
3.
Hydrolysis of _________ drives the formation of UDP-glucose.
Ans: j
Section: 25.1
4.
____________ Glucosyl units are added to this end or terminal of glycogen.
Ans: b
Section: 25.1
5.
____________ is the key regulatory enzyme in glycogen synthesis.
Ans: g
Section: 25.1
6.
Glycogen ____________is inhibited by phosphorylase kinase.
Ans: c
Section: 25.2
7.
____________ dissociates from phosphorylase a in the T state.
Ans: i
Section: 25.2
Ans: d
Section: 25.1
Chapter 25 Glycogen Synthesis
2
8.
____________is the storage disease that results in cramps with light exercise.
9.
____________ This protein serves as the primer used by glycogen synthase.
Ans: e
Section: 25.1
10.
____________ is the glycogen storage disease where the defective enzyme is glucose 6-
phosphatase.
Ans: f
Section: 25.2
Fill–in-the-Blank Questions
11.
_____ acts as a “high–energy handle” for biosynthetic reactions including glycogen synthesis.
Ans: UDP Section: 25.1
12.
The reaction catalyzed by _____ transfers UDP-glucose to the hydroxyl of an existing glycogen
core.
Ans: glycogen synthase Section: 25.1
13.
_____ is the protein that can self-glycosylate with up to 10–20 glucose units
Ans: Glycogenin Section: 25.1
14.
In general, phosphorylated forms of glycogen synthase lead to _____ levels of glycogen.
Ans: decreased Section: 25.2
15.
There is a high _____-to-insulin ratio in diabetes.
Ans: glycogen Section: 25.2
16.
Glycogen synthase catalyzes the transfer of a glucose residue from UDP-glucose to one of the
_____ ends of glycogen.
Ans: non-reducing Section: 25.1
17.
The glycogen branching enzyme moves a block of _____ (or so) glucose residues to form a
branch point at least four residues from a pre-existing branch.
Ans: seven Section: 25.1
18.
Glycogen synthase is converted into the active form by the action of _____.
Ans: protein phosphatase 1, PP1 Section: 25.2
19.
The complete oxidation of a glucose residue from glycogen produces _____ ATP.
Ans: 31 Section: 25.1
20.
Insulin stimulates glycogen synthase by inactivating _____.
Ans: glycogen synthase kinase Section: 25.2
Ans: l
Section: 25.2
Chapter 25 Glycogen Synthesis
3
Multiple-Choice Questions
21.
The activated glucose donor of glycogen synthesis is:
A)
glucose 1-phosphate.
D)
UTP.
B)
glucose.
E)
None of the above.
C)
ATP.
22.
At the center of a glycogen molecule is:
A)
glucose.
D)
glycogen synthase.
B)
glygogenin.
E)
glycogen phosphorylase.
C)
UDP-glucose.
Ans: B Section: 25.1
23.
What enzyme(s) is (are) required to synthesize -1,4-glycosidic bonds in glycogen?
A)
glycogen synthase
D)
A and B
B)
UDP-glucose phosphorylase
E)
B and C
C)
branching enzyme
Ans: A Section: 25.1
24.
Glycogenin:
A)
consists of dimmer proteins.
D)
B and C
B)
self assembles 10-20 glycosyl units.
E)
All of the above.
C)
is the primer for glycogen synthase.
Ans: E Section: 25.1
25.
The _______________ creates a 1,6-glycosidic link.
A)
branching enzyme
D)
glycogen synthase
B)
glucose transferase
E)
None of the above.
C)
glycogen isomerase
Ans: A Section: 25.1
26.
The enzyme that begins the kinase cascade activating glycogen degradation is:
A)
glycogen synthase
D)
PKA
B)
phosphorylase kinase
E)
tyrosine kinase
C)
PKC
Ans: D Section: 25.2
27.
Which is the true glucose level sensor in the cell?
A)
insulin
D)
glycogen synthase
B)
phosphorylase a
E)
protein phosphatase I
C)
glucagon
Ans: B Section: 25.2
28.
An incorrect, tight binding of PP1 to glycogen synthase would result in
A)
a hyperactive glycogen synthase.
D)
high blood glucose.
B)
hyper-glycogen levels.
E)
activated glycogen synthase.
C)
increased in insulin action
Ans: B Section: 25.2
Ans: E Section: 25.1
Chapter 25 Glycogen Synthesis
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29.
After exercise, muscle cell glycogen metabolism is regulated by:
A)
insulin.
D)
glycogen synthase
B)
phosphorylase a
E)
protein phosphatase 1
C)
glucagon
30.
___________ results from a loss or inactive insulin receptors
A)
Hypoglycemia
D)
Type II diabetes.
B)
Hyperinsulinemia
E)
None of the above.
C)
Type I diabetes
Ans: D Section: 25.2
31.
Which of the following occur after a carbohydrate–rich meal?
A)
Blood-glucose levels increase leading to glycogen storage in the liver.
B)
Blood-glucose levels increase leading to glycogen storage in the muscle.
C)
Glycogen storage in the muscle shuts down.
D)
All of the above.
E)
None of the above.
Ans: A Section: 25.2
32.
Type I diabetes leads to ___________ in the liver.
A)
increased glucose transport
D)
decrease in gluconeogenesis
B)
increased glycogen synthesis
E)
All of the above.
C)
decrease in fructose 2,6-phosphate
Ans: C Section: 25.2
33.
ATP is known as the energy currency of the cell; however, ATP is not used directly in any of
the enzymatic reactions in glycogen synthesis. How then does ATP provide energy currency for
glycogen synthesis?
A)
ATP is used to regenerate GTP in the cGMP cascade.
B)
ATP is used by the diphosphokinase to regenerate UTP.
C)
Dietary glucose is phosphorylated to glucose 1-phosphateby hexokinase.
D)
The branching enzyme requires the hydrolysis of ATP.
E)
An activated glucosyl unit of ADP-glucose is transferred to the hydroxyl group at c-4 of a
terminal residue within a chain of glycogen.
Ans: B Section: 25.1
34.
Why would you expect the amount of glycogen in type I glycogen-storage disease (von Gierke
disease) to be increased?
A)
Glycogen phosphatase is activated by increases in glucose 6-phosphate.
B)
Glucose 6-phosphatase is the final step in glycogenolysis. Thus, glucose 6-phosphate, the
first metabolite in glycogen synthesis, remains high.
C)
Epinephrine inhibition of glycogen synthesis is defective.
D)
cAMP inhibition of glycogen synthesis is defective.
E)
The R form of glycogen synthase is stabilized permanently.
Ans: B Section: 25.2
Ans: E Section: 25.2
Chapter 25 Glycogen Synthesis
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35.
Glycogen metabolism is regulated, up to a point, by a cyclic AMP cascade. At what point do
glycogen synthesis pathways diverge from glycogen degradation pathways?
A)
Phosphorylase kinase converts phosphorylase b to phosphorylase a and glycogen
synthase a to glycogen synthase b.
B)
Protein kinase A leads to the activation of glycogen degradation, and also the inhibition
of glycogen synthase by conversion from a to b.
C)
Phosphorylase kinase converts phosphorylase a to phosphorylase b and glycogen
synthase a to glycogen synthase b.
D)
Protein kinase A leads to the activation of glycogen degradation, and also the inhibition
of glycogen synthase by conversion from b to a.
E)
Cyclic AMP converts inactive PKA to active PKA, causing the inactivation of
phosphorylase kinase.
36.
Predict the major consequence of the loss of the gene that encodes the glycogen-targeting
subunit of protein phosphatase 1.
A)
Protein kinase A would not be inhibited from phosphorylating PP1.
B)
Glycogen synthase a will be fixed in the T form.
C)
Phosphorylase kinase will be activated only in the presence of cAMP.
D)
Glucose 6-phosphatase will display reduced activity.
E)
Loss of this gene would prevent association of the catalytic subunit of PP1 from its
substrate.
Ans: E Section: 25.2
Short-Answer Questions
37.
Draw the substrates and products for glycogen synthesis and indicate where insulin and
glucagon coordinate both pathways.
Ans:
Use the pathways in Figures 25.2, 25.3, and 25.6 and indicate the effect of agonists
cAMP and PKA on phosphorylase and synthase.
Sections: 25.1 and 25.2
38.
Using thermodynamic terms, describe the mechanism by which UDP-glucose is formed.
will use the energy of hydrolysis to drive PPi + H2O → 2 Pi. This leads to a very low
product for the UDP transferase activity as there will be almost no PPi found in the cell.
Section: 25.1
39.
How are new glucosyl units added to a growing glycogen molecule?
Ans:
Glucosyl units are added to the non-reducing ends, resulting in an increase in efficiency
in synthesis and degradation.
Section: 25.1
40.
Type I diabetes is often called fasting in the sea of plenty. Explain?
kidney cell in a starvation state. Kidney cells will become ketogenic, even though the
blood glucose level is sufficiently high.
Section: 25.2
Ans: B Section: 25.2
Chapter 25 Glycogen Synthesis
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41.
Explain the conversion between both a and b, R and T forms of phosphorylase.
42.
There is a rare disease where a critical serine in muscle glycogenin is mutated to alanine, which
results in what biochemical outcome?
Ans:
The muscle isoform of glycogen will not be phosphorylated by PKA at serine. This will
unphosphorylated, a hyperactive PP1, and result in high levels of glycogen.
Section: 25.2
43.
Insulin binds to its receptor and causes what protein to be activated in the cytoplasm?
Ans:
insulin receptor substrate
Section: 25.2
44.
Explain how the liver responds to muscle challenges during insulin dependent diabetes.
Ans:
The liver primarily responds by increasing gluconeogenesis and glycogenolysis.
Section: 25.2
45.
Explain why patients with McArdle’s disease do not accumulate lactate during light exercise?
Ans:
The glycolytic rate is lower than in normal patients because of the lack of glucose from
glycogen.
Section: 25.2
46.
Give the reaction catalyzed by UDP-glucose pyrophosphorylase.
Ans:
Section: 25.1
47.
The reaction, glucose-1-phosphate + UTP UDP-glucose + PPi, is readily reversible.
Explain how the formation of UDP-glucose from glucose-1-phosphate and UTP is essentially
reversible.
+ UTP UDP-glucose + 2 Pi, which is very exergonic.
Section: 25.1
48.
How does insulin stimulate glycogen synthesis?
and thus inactivate glycogen synthase kinase. Under these conditions the PPi removes
25.20.
Section: 25.2
using the appropriate markings, show how phosphorylase kinase switches a and b form.
Include the hormonal regulation of this control and R and T conformation switches.
Section: 25.2 and Figure 25.8
Chapter 25 Glycogen Synthesis
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49.
What did Carl and Gerty Cori discover about the cause of von Gierke disease? Briefly explain
how this information helps to explain the symptoms of the disease.
50.
How does insulin act on glycogen synthesis?
synthase in its phosphorylated, less active state.
Section: 25.2
blood.
Section: 25.2