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An amino acid is an organic compound characterized by having a carboxyl group, amino group, and side-chain attached to a central carbon atom. Amino acids are used as precursors for other molecules in the body. Linking amino acids together forms polypeptides, which may become proteins. Amino acids are made from genetic code in the ribosomes of eukaryotic cells. The genetic code is a code for proteins made within cells. DNA is translated into RNA. Three bases (combinations of adenine, uracil, guanine, and cytosine) code for an amino acid. There is more than one code for most amino acids. Some amino acids may not be made by an organism. These "essential" amino acids must be present in the organism's diet. In addition, other metabolic processes convert molecules into amino acids. (责任编辑：) |