..... Click the link for more information. ) analogous in chemical structure to cellulose cellulose, chief constituent of the cell walls of plants. Chemically, it is a carbohydrate that is a high molecular weight polysaccharide. Raw cotton is composed of 91% pure cellulose; other important natural sources are flax, hemp, jute, straw, and wood.
..... Click the link for more information. , consists of units of a glucose derivative (N-acetyl-d-glucosamine) joined to form a long, unbranched chain. Like cellulose, chitin contributes strength and protection to the organism. In arthropods the chitinous shell, or exoskeleton, covers the surface of the body, does not grow, and is periodically cast off (molted). After the old shell is shed, a new, larger shell is secreted by the epidermis, providing room for future growth. The chitin is rigid except between some body segments and joints where it is thin and allows movement of adjacent parts. Chitin is also found in the cell walls of some fungi.
chitin
White, horny substance found in the external skeleton of crabs, lobsters, and many insects; in internal structures of some other invertebrates; and in some fungi, algae, and yeasts. It is a polysaccharide, the monomer unit being glucosamine. It is used industrially in purifying wastewater, thickening and stabilizing foods and pharmaceuticals, and sizing and strengthening paper, and as a wound-healing agent, an ion-exchange resin, a membrane for industrial separations, and a binder for dyes, fabrics, and adhesives.
chitin
Chitin
A polysaccharide found abundantly in nature. Chitin forms the basis of the hard shells of crustaceans, such as the crab, lobster, and shrimp. The exoskeleton of insects is also chitinous, and the cell walls of certain fungi contain this substance.
Chitin is a long, unbranched molecule consisting entirely of N-acetyl- d -glucosamine units linked by β-1,4 bonds (see illustration). It may be thought of as cellulose in which the hydroxyl groups on the second carbon are replaced with NHCOCH3 groups. Chitin is considered to be synthesized in nature by an enzyme which is capable of effecting a glycosyl transfer of the N-acetyl- d -glucosamine from uridinediphosphate-N-acetyl- d -glucosamine to a preformed chitodextrin acceptor, forming the polysaccharide. This stepwise enzymic transfer results in the production of the long chain of β-N-acetyl- d -glucosamine units, which is insoluble chitin. See Polysaccharide
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