Introduction to glycogen and glucose
Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals and fungi. The polysaccharide structure represents the main storage form of glucose in the body. In humans, glycogen is made and stored primarily in the cells of the liver and the muscles hydrated with three or four parts of water. Glycogen functions as the secondary long-term energy storage, with the primary energy stores being fats held in adipose tissue. Muscle glycogen is converted into glucose by muscle cells, and liver glycogen converts to glucose for use throughout the body including the central nervous system. Glycogen is the analogue of starch, a glucose polymer that functions as energy storage in plants. It has a structure similar to amylopectin (a component of starch), but is more extensively branched and compact than starch. Both are white powders in their dry state. Glycogen is found in the form of granules in thecytosol/cytoplasm in many cell types, and plays an important role in the glucose cycle. Glycogen forms an energy reserve that can be quickly mobilized to meet a sudden need for glucose, but one that is less compact than the energy reserves of triglycerides (lipids).In the liver, glycogen can compose from 5 to 6% of its fresh
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Glycogen phosphorylase manages to use phosphate to catalyze glycogen breakdown by employing the coenzyme pyridoxal phosphate (PLP). This coenzyme forms a Schiff base intermediate with a lysine residue of the enzyme. The 5' phosphate of PLP act as a proton donor and then as a proton acceptor (acid-base catalyst). Orthophosphate acts to donate a proton to carbon 4 of the glycogen chain and simultaneously acquire a proton from PLP. The carbonium ion thus created is attacked by orthophosphate to form alpha-glucose-1-phosphate.
Regulation of Glycogen