Carbohydrates

Carbohydrates are a class of organic molecules with the general chemical formula C_n(H₂O)_n. These compounds are literally carbon hydrates. Only the monomeric form of these compounds, the monosaccharides, fit this description precisely. Two monosaccharides can be polymerized together through a glycosidic linkage to form a disaccharide. When a few monosaccharide molecules are polymerized together, the result is an oligosaccharide. A polysaccharide is an extensive polymer of carbohydrate monomers. The monosaccharide glucose is our primary energy source. The function of the polysaccharides starch (plants) and glycogen (animals) is to store glucose in a readily accessible form, as well as lower the osmotic potential of internal fluids. Some polysaccharides serve a structural role in living organisms. The glucose polymer cellulose is a major component of plant cell walls. Chitin, a polymer of N-acetylglucosamine, is a major structural component of the exoskeleton of insects and crustaceans. Hyaluronic acid and chondroitin sulfate occur in the connective tissues of animals, especially in cartilage. Oligosaccharide side chains of glycoproteins may also serve as signals for intracellular sorting of the protein (i.e., mannose-6-phosphate signal designating lysosomal enzymes).