glycogen (redirected from animal starch)

glycogen (glī`kəjən), starchlike polysaccharide (see carbohydrate) that is found in the liver and muscles of humans and the higher animals and in the cells of the lower animals. Chemically it is a highly branched condensation polymer of glucose; it is readily hydrolyzed to glucose. Glycogen is formed by the liver from glucose in the bloodstream and is stored in the liver; conversion of glucose to glycogen (glycogenesis) and hydrolysis of glycogen to glucose (glycogenolysis) together are the usual mechanism for maintenance of normal levels of blood sugar. Glycogen is also produced by and stored in muscle cells; during short periods of strenuous activity, energy is released in the muscles by direct conversion of glycogen to lactic acid. During normal activity, energy is released by metabolic oxidation of glucose to lactic acid.

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glycogen

Principal storage carbohydrate of animals, occurring primarily in the liver and resting muscles. It is also found in various bacteria, fungi, and yeasts. Glycogen is a branched polysaccharide, a long chain of glucose units, into which it is broken down when energy is needed.

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glycogen

a polysaccharide consisting of glucose units: the form in which carbohydrate is stored in the liver and muscles in man and animals. It can easily be hydrolysed to glucose

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glycogen [′glī·kə·jən]

(biochemistry)

A nonreducing, white, amorphous polysaccharide found as a reserve carbohydrate stored in muscle and liver cells of all higher animals, as well as in cells of lower animals.

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Glycogen

The primary reserve polysaccharide of the animal kingdom. It is found in the muscles and livers of all higher animals, as well as in the cells of lower animals. Because of its close relationship to starch, it is often called animal starch, although glycogen is found in some lower plants, fungi, yeast, and bacteria. See Starch

Glycogen is a nonreducing, white, amorphous polysaccharide which dissolves readily in cold water, forming an opalescent, colloidal solution. The molecular weight of glycogen is usually very high, and it varies with the source and the method of preparation; molecular weights of the order of 1-20 × 10⁶ have been reported. Chemical studies show glycogen to possess a branched structure similar to the amylopectin starch fraction.

In its biochemical reactions, glycogen is similar to starch. It is attacked by the same plant amylases that attack starch, and like starch, it is degraded to maltose and dextrins. Both glycogen and starch are broken down by animal or plant phosphorylase enzyme in the presence of inorganic phosphate with the production of α- d -glucose-1-phosphate. See Carbohydrate metabolism

The metabolic formation of glycogen from glucose in the liver is frequently termed glycogenesis. In fasted animals, glycogen formation can be induced by the feeding, not only of materials that can be hydrolyzed to glucose and other monosaccharides, such as fructose, but also of various other materials. A number of l -amino acids, such as alanine, serine, and glutamic acid, upon deamination in the liver give rise to substances, such as pyruvic acid and α-ketoglutaric acid, that can be converted in the liver to glucose units which are subsequently converted to glycogen. Furthermore, substances such as glycerol derived from fats, dihydroxyacetone, or lactic acid can all be utilized for glycogen synthesis in the liver. Such noncarbohydrate precursors are termed glycogenic compounds. The process of glycogen formation from these precursors is known as glyconeogenesis. The term glycogenolysis is used to connote glycogen breakdown. See Polysaccharide