GLYCOGENESIS AND GLYCOGENOLYSIS, Lecture notes of Biochemistry

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GLYCOGENESIS AND

GLYCOGENOLYSIS

Glycogen

Storage form of glucose in animals.

Stored in the liver (6-8%) & muscle (1-2%).

Quantity more in the muscle(~250g) than

liver(75g) due to higher muscle mass.

Stored as granules in the cytosol.

Glycogenesis :- Synthesis of glycogen from glucose.

Site :- Cytosol

Activated Glucose – UDP Glucose

Glycogen primer or Glycogenin required to initiate G

Glycogenesis

GLUCOKIN ASE

PHOSPHOG LUCOMUTA SE^ G-1-PURIDYL TRANSFERAS E (^) GLYCOGEN SYNTHASE

Overall Reaction of Glycogenesis :-

(Glucose)n + Glucose + 2 ATP

(Glucose)n+1 + 2 ADP + Pi

Regulation of glycogenesis & Glycogenolysis Key enzyme of Glycogenesis- Glycogen Synthase Key enzyme of Glycogenolysis- Glycogen Phosphorylase

Three Regulatory Mechanisms

1. Allosteric Regulation.
2. Hormonal Regulation.
3. Influence of Calcium.

Allosteric Regulation of Glycogen Metabolism :- When substrate availability & energy level is high, Glycogen synthesis is increased. When glucose concentration is low & energy level low, Glycogen breakdown is enhanced. In well-fed state, Glucose- 6 - P allosterically activates Glycogen Synthase. At the same time, allosterically inhibits Glycogen Phosphorylase. Free Glucose in the liver is also a allosteric inhibitor of Glycogen Phosphorylase.

Hormonal Regulation of Glycogen Metabolism :- Hormones control Glycogen synthesis & degradation by covalent modification ie., phosphorylation & Dephosphorylation. cAMP acts as second messenger. cAMP activates Protein Kinase. Protein Kinase causes phosphorylation of enzymes, either activating or deactivating them.

Allosteric Regulation of Glycogen Metabolism :- When substrate availability & energy level is high, Glycogen synthesis is increased. When glucose concentration is low & energy level low, Glycogen breakdown is enhanced. In well-fed state, Glucose- 6 - P allosterically activates Glycogen Synthase. At the same time, allosterically inhibits Glycogen Phosphorylase. Free Glucose in the liver is also a allosteric inhibitor of Glycogen Phosphorylase.