carbohydrate

carbohydrate, any member of a large class of chemical compounds that includes sugars, starches, cellulose, and related compounds. These compounds are produced naturally by green plants from carbon dioxide and water (see photosynthesis). Carbohydrates are important as foods; they supply energy and are used in the production of fats. They are also used in various forms in industry and commerce. There are three main classes of carbohydrates. Monosaccharides are the simple sugars, e.g., fructose and glucose; they have the general formula (CH₂O)_n, in which n is an integer larger than 2. Disaccharides include lactose, maltose, and sucrose. Upon hydrolysis, a disaccharide molecule yields two monosaccharide molecules. Most disaccharides have the general formula C_n(H₂O)_n−1, with n larger than 5. Polysaccharides include such substances as cellulose, dextrin, glycogen, and starch; they are polymeric compounds made up of the simple sugars and can be hydrolyzed to yield simple sugars. The disaccharides are sometimes grouped with the simpler polysaccharides (usually those made up of three or four simple sugar units) to form a class of carbohydrates called the oligosaccharides.

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carbohydrate

Any member of a very abundant and widespread class of natural organic compounds that includes sugars, starch, and cellulose. They are commonly classified as monosaccharides (simple sugars; e.g., glucose, fructose), disaccharides (2-unit sugars; e.g., sucrose, lactose), oligosaccharides (3–10 or so sugars), and polysaccharides (large molecules with up to 10,000 monosaccharide units, including cellulose, starch, and glycogen). Green plants produce carbohydrates by photosynthesis. In most animals, carbohydrates are the quickly accessible reservoir of energy, and oxidation (see oxidation-reduction) of glucose in tissues supplies energy for metabolism. Many (but by no means all) carbohydrates have the general chemical formula C_n(H₂O)_n. The carbon (C) atoms are bonded to hydrogen atoms (−H), hydroxyl groups (−OH; see functional group), and carbonyl groups (−C=O), whose combinations, order, and geometric arrangement lead to a large number of isomers with the same chemical formula but different properties. The class is further enlarged because each isomer has various derivatives: uronic acids, sugars with an oxidized group; sugar alcohols, sugars with a reduced group; glycosides, compounds of sugars with other molecules containing a hydroxyl group; and amino sugars, sugars with an amino group (see amino acid).