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protein
(pro´tēn)
any large organic compound made from one or more polypeptides (chains of amino acids joined by peptide linkages between the amino group of one and the carboxylic acid group of the next). The primary structure
of a polypeptide chain is the sequence of amino acids and is determined by the sequence of bases in the deoxyribonucleic acid (DNA) of its gene. Proteins in the body are essential to its structure and function. Structures such as cell walls, various membranes, connective
tissue, and muscles are mainly protein. None of the cells of the body can survive without an adequate supply of protein; in
fact, proteins constitute about 20 per cent of the cell mass. Some hormones and enzymes are proteins, and blood plasma contains many important proteins (see plasma proteins).
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