10. Glycogen metabolism- Glycogenesis and Glycogenolysis

Glycogen metabolism

Glycogen
Homopolysaccharide of glucose with alpha 1-4 glycosidic linkage in linear chain and alpha 1-6 at branching point
Branching make molecule more globular, compact and less space consuming

Metabolism includes
1. Glycogenesis
2. Glycogenolysis

Glycogenesis
Synthesis of glycogen from glucose
Key enzyme- glycogen synthase

Steps
1. Activation of glucose to UDP-glucose
2. Addition of glucose to primer/ glycogenin
3. Elongation up to 10 to 12 glucose units
4. Branching by forming alpha 1-6 linkage by branching enzyme
5. Elongation
6. Branching
7. Glycogen

Glycogenolysis
Synthesis of glucose from glycogen
Key enzyme- glycogen phosphorylase

Steps
1. Removal of glucose in the form of glucose 1 phosphate
2. Limit dextrin formation
3. Transfer of trisaccharide unit from branching point to linear chain by transferase
4. Breaking of alpha 1-6 linkage and liberation of Free glucose by debranching enzyme
5. Again removal of glucose in the form of glucose 1 phosphate
6. Conversion of glucose 1 phosphate to glucose 6 phosphate
7. Glucose formation

REGULATION

glycogen synthase active in dephosphorylated state
And
Glycogen phosphorylase active in phosphorylated state

Insulin favours the glycogenesis by decreasing cAMP and glucagon favours glycogenolysis by increasing cAMP

Glycogenesis is inhibited by Glucagon in Liver