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Glycogen: The Body's Primary Glucose Storage Polymer

Glycogen is a highly branched polysaccharide of glucose, serving as the main short-term energy reserve in animals. It is the storage form of carbohydrate in humans.

Structure

α-1,4-glycosidic bonds in linear chains.
α-1,6-glycosidic bonds at branch points (every 8-12 residues).
Compact, spherical granules allowing rapid enzymatic access.

Storage Sites and Roles

Metabolic Regulation

Glycogenesis (synthesis): Insulin-activated glycogen synthase (fed state).
Glycogenolysis (breakdown): Glucagon (liver) / epinephrine (muscle) → PKA → phosphorylase kinase → glycogen phosphorylase.

Glycogen provides rapid glucose mobilization (seconds to minutes), bridging the gap between meals and sustaining exercise.

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Tissue	Amount (Adult)	Function
Liver (~100-120g)	~5-6% of wet weight	Maintains blood glucose for whole body (brain, RBCs) via glycogenolysis & gluconeogenesis.
Skeletal Muscle (~400-500g)	~1-2% of wet weight	Fuels local muscle contraction; cannot release free glucose (lacks glucose-6-phosphatase).