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 Cn(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).
Monosacchride
Any of the simple sugars that serve as building blocks for carbohydrates.
They are classified based on their backbone of carbon (C) atoms: Trioses have three carbon atoms, tetroses four, pentoses five, hexoses six, and heptoses seven. The carbon atoms are bonded to hydrogen atoms (−H), hydroxyl groups (−OH; see functional group), and carbonyl groups (−C=O), whose combinations, order, and configurations allow a large number of stereoisomers (see isomer) to exist. Pentoses include xylose, found in woody materials; arabinose, found in gums from conifers; ribose, a component of RNA and several vitamins; and deoxyribose, a component of DNA. Important hexoses include glucose, galactose, and fructose. Monosaccharides combine with each other and other groups to form a variety of disaccharides, polysaccharides, and other carbohydrates.
Polysaccharide
Any of a large class of long-chain sugars composed of monosaccharides.
Because the chains may be unbranched or branched and the monosaccharides may be of one, two, or occasionally more kinds, polysaccharides can be categorized in various ways. Cellulose, starch, glycogen, and dextran are all polysaccharides of glucose, with different configurations. Pectins are composed of a galactose derivative, chitin of a glucose derivative. Connective tissues, joint fluid, and cartilage contain two-component polysaccharides, including heparin. See also oligosaccharide.
Galactose
Organic compound, a monosaccharide, chemical formula C6H12O6.
It is usually found in nature combined with other sugars, for example, in lactose, in polysaccharides, and in glycolipids, carbohydrate-containing lipids that occur in the brain and other nervous tissues of most animals. It has uses in organic synthesis and in medicine.
Fructose
levulose fruit sugar
Organic compound, one of the simple sugars (monosaccharides), chemical formula C6H12O6.
It occurs in fruits, honey, syrups (especially corn syrup), and certain vegetables, usually along with its isomer glucose. Fructose and glucose are the components of the disaccharide sucrose (table sugar); hydrolysis of sucrose yields invert sugar, a 50:50 mixture of fructose and glucose. The sweetest of the common sugars, fructose is used in foods and medicines.
Source: Britannica encyclcopedia
