Doudoroff, Michael Department of Bacteriology, University of California, Berkeley, California.
Last reviewed:April 2019
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- Dietary carbohydrates
- Intestinal absorption and transport
- Dissimilation of simple sugars
- Oxidative mechanisms
- Simple sugars other than glucose
- Disaccharides and polysaccharides
- Links to Primary Literature
- Additional Readings
The sum of the biochemical and physiological processes involved in the breakdown and synthesis of simple sugars, oligosaccharides, and polysaccharides, and in the transport of sugars across cell membranes and tissues. The basic chemistry of carbohydrates is metabolically important. The breakdown or dissimilation of simple sugars (particularly glucose) that occurs during carbohydrate metabolism is one of the principal sources of energy for living organisms (Fig. 1). The dissimilation may be anaerobic, as in fermentations, or aerobic, that is, respiratory. In both types of metabolism, the breakdown is accompanied by the formation of energy-rich bonds, chiefly the pyrophosphate bond of the coenzyme adenosine triphosphate (ATP), which serves as a coupling agent between different metabolic processes. In higher animals, glucose is the carbohydrate constituent of blood, which carries it to the tissues of the body. In higher plants, the disaccharide sucrose is often stored and transported by the tissues. Certain polysaccharides, especially starch and glycogen, are stored as endogenous food reserves in the cells of plants, animals, and microorganisms. Others, such as cellulose, chitin, and bacterial polysaccharides, serve as structural components of cell walls. As constituents of plant and animal tissues, various carbohydrates become available to those organisms that depend on other living or dead organisms for their source of nutrients. All naturally occurring carbohydrates can be dissimilated by some animals or microorganisms. See also: Adenosine triphosphate (ATP); Biochemistry; Blood; Carbohydrate; Cellulose; Energy metabolism; Glucose; Glycogen; Metabolism; Nutrition; Oligosaccharide; Polysaccharide; Starch; Sugars (sweeteners)
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