• 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
  • 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
  • Glycogen is found in the form of granules in the cytosol / 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 comprise from 5 to 6% of its fresh weight (100–120 g in an adult)
  • Only the glycogen stored in the liver can be made accessible to other organs
  • In the muscles, glycogen is found in a low concentration (1-2% of the muscle mass)
  • The amount of glycogen stored in the body—especially within the muscles, liver, and red blood cells mostly—depends on physical training, basal metabolic rate, and eating habits
  • Small amounts of glycogen are found in the kidneys, and even smaller amounts in certain glial cells in the brain and white blood cells
  • The uterus also stores glycogen during pregnancy to nourish the embryo
  • Glycogen is a branched biopolymer consisting of linear chains of glucose residues with further chains branching off every 8 to 12 glucoses or so
  • Due to the way glycogen is synthesised, every glycogen granule has at its core a glycogenin protein
  • When it is needed for energy, glycogen is broken down and converted again to glucose
  • Glycogen phosphorylase is the primary enzyme of glycogen breakdown
  • Glucagon, another hormone produced by the pancreas, in many respects serves as a countersignal to insulin
  • In response to insulin levels being below normal (when blood levels of glucose begin to fall below the normal range), glucagon is secreted in increasing amounts and stimulates both glycogenolysis (the breakdown of glycogen) and gluconeogenesis
  • Muscle cell glycogen appears to function as an immediate reserve source of available glucose for muscle cells
  • Glycogen was discovered by Claude Bernard
  • Soon after the discovery of glycogen in the liver, A. Sanson found that muscular tissue also contains glycogen
  • The empirical formula for glycogen of (C6H10O5)n was established by Kekule in 1858
  • Glycogen synthesis is, unlike its breakdown, endergonic – it requires the input of energy



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