Department of Biochemistry, Nepalgunj Medical College

Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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MBBS II

Biomedical importance

Major storage of carbohydrate in animals. It is branched polymer of a-D-glucose.

Provides readily available source of glucose 1-phosphate for glycolysis within muscle itself.

Liver glycogen functions to store and export glucose to maintain blood glucose concentration in fasting state.

Glycogen storage diseases are a group of inherited disorders characterized by deficient mobilization of glycogen or deposition of abnormal forms of glycogen, leading to liver damage, muscle weakness or even early death.

Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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Function of Glycogen metabolism

Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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Structure of glycogen

Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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• … is branched chain homopolymer

made exclusively from a-D-glucose.

• Primarily glycosidic bond is an

a(14) linkage.

• There is a(16) branching after

every eight-ten glycoslyl residues.

• Molecular mass: 108 daltons.

Glycogenesis occurs mainly in liver &muscle

Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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Glycogen

biosynthesis

involves UDP-

glucose.

Uridine diphosphate glucose

Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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Pathways of

glycogenesis and

glycogenolysis in

the liver

Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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Glycogen molecule

Glycogenin

Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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1. 37 kDa protein.

2. Functions as a primer for

glycogen synthesis.

3. Present at the core of the

glycogen molecule in

muscle but not in liver.

Branching of glycogen

Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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Branching

involves

detachment of

existing glycogen

chains

Amylo-a(14) a(16)-transglucosidase

Glycogenolysis is not the reverse of glycogenesis, but is a separate pathway

Glycogen phosphorylase catalyzes

the rate-limiting step in

glycogenolysis.

Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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Glycogenolysis

1. Shortening of the chain

2. Removal of branches

3. Conversion of glucose 1-phosphate to glucose 6-

phosphate

4. Lysosomal degradation of glycogen

Sunday, February

19, 2017Rajesh Chaudhary | Lecturer

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Sunday, February

19, 2017Rajesh Chaudhary | Lecturer

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1. First, Oligo-a(14)

a(14) glucan

transferase

2. Second, amylo-a(16)-

glucosidase

Glycogen storage diseases

Saturday, February

18, 2017Rajesh Chaudhary | Lecturer

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Type Name Enzyme deficiency Clinical features

Ia Von Gierker’s disease Glucose 6-phosphatase Glycogen accumulation in liver and renal-

tubule cells; hypoglycemia, lactic acidemia,

ketosis and hyperlipemia

II Pompe’s disease Lysosomal a1 4 and a16

glucosidase

Accumulation of glycogen in lysosome, juvenile

onset variant, muscle hypotonia, death from

heart failure by age 2, muscle dystrophy

IIIa Limit dextrinosis, Frobe’s

or Cori’s disease

Liver and muscle debranching

enzyme

Fasting hypoglycemia, hepatomegaly in

infancy; muscle weakness

VI Hers’ disease Liver phosphorylase Hepatomegaly, accumulation of glycogen in

liver, mild hypoglycemia

Allosteric regulation of glycogen synthesis and degradation

Sunday, February

19, 2017Rajesh Chaudhary | Lecturer

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Activation of glycogen degradation in muscle by calcium

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19, 2017Rajesh Chaudhary | Lecturer

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18, 2017Rajesh Chaudhary | Lecturer

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References

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18, 2017Rajesh Chaudhary | Lecturer

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