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Lecture 4

BIOC 3300 Lecture Notes - Lecture 4: Glycogen Phosphorylase, Glycogen Synthase, Pyridoxal Phosphate

Biochem & Molecular Biology
Course Code
BIOC 3300
Mc Leod Roger

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1. Where does glycogen
In the liver and skeletal muscle.
(a) Glycogen is major energy source
for contraction of skeletal muscle
(b) in liver glycogen is stored to
maintain blood glucose. About 2-8%
of liver weight is glycogen.
2. Glycogen 1. the major energy source for
contraction of skeletal muscle.
2. the major energy source stored in
the liver to maintain blood glucose
3. Bond involved in
mobilization of
Phosphorolysis of α-1,4-glycosidic
linkages of the glycogen polymer
4. reactions involved in
mobilization of
5. What enzymes are
involved in
mobilization of
Glycogen phosphorylase;
Debranching enzyme;
Phosphoglucomutase (in muscle);
Glucose-6-phosphatase (in liver).
6. Glycogen
Catalyses the reaction releasing
glucose-1-P from the non-reducing
end of glycogen.
- cannot break down α1,6 linkages at
branch points.
- phosphorylase stops at a point 4
glucose residues away from the
- pyridoxal phosphate is a cofactor.
- Reaction is near equilibrium but
high concentration of Pi makes
forward reaction favoured
7. Debranching enzyme Required to mobilize at
8. What two activities
does debranching
enzyme have?
α1,4- α1,4-glucantransferase.
-glucantransferase activity transfers
triglucose from the branchpoint
chain to another outer branch.
- α1,6-glucosidase activity releases
glucose from the branchpoint.
9. What are the
products in
mobilization of
Products of glycogen breakdown are
predominantly glucose-1-P with
some glucose (amount depends on
number of branchpoints)
10. Phosphoglucomutase Only in muscle.
Converts glucose-1-P to glucose-6-P
for entry to glycolysis.
11. Why
only exists in muscle?
To keep glucose-6-P in muscle and offer
energy by glycolysis for muscle activity.
12. Glucose-6-
Only in the liver.
Generate glucose from
glucose-6-P for transport in the blood
13. Why Glucose-6-
phosphatase only
exists in muscle?
To release glucose-6-P to the blood and
offer energy for the brain.
14. What is the building
units for glycogen
15. UDP-glucose
UDP-glucose is synthesized from glucose-
1-P by UDP-glucose pyrophosphorylase.
Released PPi is hydrolysed to 2Pi by
abundant pyrophosphatase, driving
reaction to ompletion.
The reaction is a phosphoanhydride
exchange in which the phosphoryl
oxygen of G1P attacks the
phosphorus atom of UTP to form UDPG
and release PPi. The PPi is rapidly
hydrolyzed by inorganic
16. How is glycogen
assembly initiated?
Glycogen assembly is initiated by
addition of a short chain (up to 8) of
glucose residues onto the
protein glycogenin.
glycogenin-glucose chains serve as
"primers" for glycogen synthase to
extend with additional UDPglucose
17. glycogenin
Serve as "primers" for
glycogen synthase to extend
18. What are enzymes
used in glycogen
Glycogen Synthase.
Branching Enzyme.
Lec 4 Slides - Glycogen Metabolism and Gluconeogenesis
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