Carbohydrates
Carbohydrates are a class of organic molecules with the general chemical
formula Cn(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).