1. Composition
Monomers: Glycogen is a polysaccharide composed of glucose monomers.
Linkages: It consists of α-D-glucose units linked by α-1,4-glycosidic bonds (linear chains) and α-1,6-glycosidic bonds (branch points).
2. Structure
Linear Chains: The main structure of glycogen consists of linear chains of glucose molecules linked by α-1,4-glycosidic bonds.
Branching: Branch points occur due to α-1,6-glycosidic bonds, creating a highly branched structure.
Degree of Branching: Glycogen has a more branched structure than amylopectin, with branches occurring approximately every 8 to 12 glucose units.
3. Branching Enzyme (Amylo-(1,4→1,6)-transglycosylase)
Function: The enzyme responsible for branching in glycogen is amylo-(1,4→1,6)-transglycosylase.
Catalytic Activity: It cleaves a segment of the linear chain and transfers it to the C-6 position of a glucose unit within the same or another chain, forming a branch point.
4. Storage Form of Glucose
Energy Reservoir: Glycogen is a primary energy storage molecule in animals, particularly in liver and muscle cells.
Rapid Mobilization: Its branched structure allows for rapid mobilization of glucose during energy-demanding activities.
5. Solubility
Insolubility: Glycogen is insoluble in water due to its large size and complex structure.
6. Molecular Weight
Large Molecule: Glycogen is a large molecule, with molecular weights ranging from several hundred thousand to a few million Daltons.
7. Synthesis and Breakdown
Synthesis (Glycogenesis): Glycogen is synthesized in cells through the process of glycogenesis, involving the addition of glucose units to the growing glycogen chain.
Breakdown (Glycogenolysis): Glycogen can be broken down into glucose through glycogenolysis, which involves the removal of glucose units from the glycogen chain.
8. Iodine Reaction
Iodine Staining: Similar to starch, glycogen forms a reddish-brown color with iodine, indicating the presence of polysaccharides.
Understanding the chemical nature of glycogen provides insights into its role as a dynamic energy reservoir in animals. The branched structure of glycogen allows for efficient storage and rapid release of glucose, contributing to the energy needs of various tissues, especially during increased demand.
