1. · It is the storage from of glucose in animals
Glycogen metabolism
·   It is the storage from of glucose in animals
·   Stored in liver (6-8%) and muscle (1-2%)
Helps to maintain the blood glucose levels,between
meals
Glycogen stores increase in a well-fed state depleted
during fasting
·  Muscle glycogen serves as a fuel reserve for the
supply of ATP during muscle contraction
In homopolysaccharide, glucose molecules held
together by - 1,4 linkages. Branch with -1, 6 linkage.
Glucokinase in liver and hexokinase in muscle which
converts glucose to glucose–6 phosphate
DR S Nayak

2. Synthesis of glycogen from glucose Occurs in liver and muscle
Glycogenesis
Synthesis of glycogen from glucose
Occurs in liver and muscle
Storage from in liver and muscle
After the meal excess glucose is converted into
glycogen
UDPG is the carrier of glucose
Glucose from UDPG is attached at the non-reducing
end of glucose molecules of glycogen primer
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3. ATP ADP Phosphoglucomutase Glucose Glu –6-P Glu-1-P Hexokinase
Glucokinase UDPG pyrophosphorylase
UTP
PPi
Uridine diphosphate glucose (UDPG)
Glycogen synthase
Glycogen primer UDP
Glycogen (1, 4 glucosyl units) n
(1, 4 and 1, Branching enzyme
Glucosyl units) n (Amylo-1, 4-1,6- transglucosidase)
(Glucosyl -4,6 transferase)
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4. Glycogenesis
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5. a specific protein,GLYCOGENIN can accept glucose
It is found that in the absence of glycogen primer,
a specific protein,GLYCOGENIN can accept glucose
from UDPG. The initial glucose is attached to the
OH group of tyrosine residue of glycogenin.
The enzyme glycogen initiator synthase
transfers the first molecule of glucose to glycogenin.
Later glycogenin itself takes up a few glucose
residues to form a fragment of primer
Branching enzyme (Amylo 1,4 –1,6 transglucosidase
transfers 6 glucose residues portion from one chain
to a neighbouring chain to form a -1,6 – linkage
DR S Nayak

6. Breakdown of glycogen to glucose ·Occurs in liver and muscle
Glycogenolysis
Breakdown of glycogen to glucose
·Occurs in liver and muscle
·End product of liver glycogenolysis is glucose
·Muscle glycogenolysis is lactate (strenuous exercise)
Muscle and brain does not contain glu-6-phosphatase
Phosphorylase Pi
Glycogen Glu-1-P
Phosphoglucomutase
Glu –6-P
Glu-6-Phosphatase H2O Pi
Glucose
DR S Nayak

7. Phosphorylase phosphorolytically splits -1,4
glucoside bonds from the outermost chains of
glycogen until 4 residues remain on either side of
– 1.6 branch point [limit dextrin]
  1.4 glucan transferase transfers 3 glucose
residue portion from one side chain to the other
exposing -1,6 branch points
Amylo 1, 6 glucosidase splits the 1,6 linkages
Acid maltase or -1,4-glucosidase (lysosomal enzyme)
degrades small quantity of glycogen. The significance of this
pathway is not clear
v                     Muscle glycogenolysis
Glycogen  Glu-1-P  Glu-6-P   glycolysis  lactate
DR S Nayak

8. Glycogenolysis
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9. Regulation of glycogenesis and glycogenolysis
·  The glycogen synthase and phosphorylase exist in
active and inactive forms
·  The dephosphorylated form of glycogen synthase is
active
·  Phosphorylated form of phosphorylase is active
The activation of phosphorylase depends on high
cAMP level. At the same time high cAMP level
inactivates glycogen synthase
Glycogen synthase b Phosphorylase a
H2O Protein phosphatase Pi
Glycogen synthase a Phosphorylase b
(Glycogenesis ON) (Glycogenolysis OFF)
DR S Nayak

10. Allosteric regulation In a well fed state Glu–6– P level is high which
activates glycogen synthase
·   On the other hand glu-6-p and ATP allosterically
inhibit phosphorylase
· Free glucose also act as inhibitor to phosphorylase
Glucose –6 –P ATP Liver glucose Muscle AMP
_ _ _
Glycogen Phosphorylase Ca2+
Glycogen Glu-1-Phosphate
Glycogen Synthase +
Glucose-6-phosphate
DR S Nayak

11. Glucagon + (Liver only) Adenylate Cyclase Adenylate Cyclase ATP cAMP
Adrenaline (Liver and muscle)
Glucagon + (Liver only)
Adenylate Cyclase Adenylate Cyclase
ATP cAMP
PPi
Protein Kinase Protein Kinase
ATP ADP ATP ADP
Phosphorylase Phosphorylase Glycogen Glycogen
Kinase kinase Synthase (a) synthase (b)
Phosphorylase (b) Phosphorylase (a)
2ATP ADP
Glycogen Glucose-1-P Pi
cAMP AMP Glycogenesis ON
+ Phosphodiesterase
Insulin
DR S Nayak

12. GLYCOGEN STORAGE DISEASES Genetic diseases [may be inherited]
Deposition of abnormal type or quantity of glycogen in the tissues
Diseases Defect and Features
Type I Glucose – 6 – phosphatase [liver]
Von Gierke’s disease Accumulation of glycogen in liver Hypoglycaemia and ketosis
Type II. Lysosomal -1, 4 – glucosidase
Pompe’s disease Glycogen accumulates in lysosomes, in all tissues
Enlarged liver and heart
Type III. Debranching enzyme [amylo -1,6-
Limit dextrinosis glucosidase
[Coris disease] Accumulation of polysaccharide
[limit dextrin] liver, heart, & muscle
TypeIV. Amylo pectinosis or Branching enzyme (glucosyl 4-6 transferase)
Andersons disease Accumulation of polysaccharide with few branch points. Cirrhosis of liver
DR S Nayak

13. Type V Muscle glycogen phosphorylase
McArdles disease Glycogen accumulates in the muscle
Diminished tolerance to exercise
Type VI. Liver glycogen Phosphorylase
Hers disease Liver enlarged
Von Gierke’s Disease
1. Fasting hypoglycemia
2. Lactic acidemia:Glucose is not synthesized from lactate produced in
muscle and liver. Lactate level increases and pH decreases
3. Hyperlipidemia: Block in gluconeogenesis leads to mobilisation fat to
meet energy requirement. So This increases free plasma FA & ketone
bodies.
4. Hyperuricemia: Accumulated glucose -6-p diverted to HMP pathway,
leading to increased synthesis of ribose and nucleotides, this enhances
metabolism of purine nucleotides and to uric acid later
5. Massive liver enlargement leads to cirrhosis
6. Children fail to grow
Given small quantity of food at frequent intervals
DR S Nayak

14. DR S Nayak