GLYCOGEN METABOLISM

DR. MD. MAHBUBUR RAHMAN

MBBS, M. Phil, MSc. (Biotechnology)

ASSISTANT PROFESSOR

DEPT. OF BIOCHEMISTRY

RAJSHAHI MEDICAL COLLEGE

After the end of the session student will able to know the

• Biomedical importance of glycogen

• Definition of glycogenosis and glycogenolysis and flow chart

• Glycogen storage disease

Glycogen

• Glycogen, the storage form of glucose, is a branched polysaccharide composed of chains of glucosyl units linked by α- 1-4 bonds with α- 1-6 branches every 8-10 residues.

BIOMEDICAL IMPORTANCE

• Muscle glycogen provides a readily available source of glucose for glycolysis within the muscle itself.

• Liver glycogen functions to store and export glucose to maintain blood glucose level between meal .

% of tissue

wt

Tissue

weight

Body

content

Liver

glycogen

5.0 1.8 kg 90 gm

Muscle

glycogen

0.7 35 kg 245 gm

Extracellular

glucose

0.1 10 L 10 gm

Characteristics of enzyme related glycogen metabolism

• Glycogen synthase is a enzyme which is activated after dephosphorylation and inactive after phosphorylation.

• Glycogen phosphorylase is activated after phosphorylation and inactivated after dephosphorylation.

Glycogenesis

a) Synthesis of UDP- Glucose

b) Synthesis of primer to initiate glycogen synthesis

c) Elongation of glycogen chain by glycogen synthatase

d) Formation of branches in glycogen

Glycogenolysis

• Shortening of chains

• Removal of Branches

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

• Lysosomal degradation of glycogen

Regulation of glycogen synthesis and degradation

• Glycogen synthesis and degradation is accomplished on two levels.

– Glycogen synthatase and glycogen phosphorylase is allosterically controlled.

– The pathway of glycogen synthesis and degradation are hormonally controlled.

Glycogen storage disease

• There are a group of genetic disease that result from a defect in an enzyme required for glycogen synthesis or degradation.

• They result either in formation of glycogen that has an abnormal structure or in the accumulation of excessive amount of normal glycogen in specific tissue as a result of impaired degradation

continuation

Example

McArdele syndrom

pompe disease

Cori disease

Von gierke disease