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4.1.1 Amino acids
Amino acids are the basic structural units of proteins. Most proteins contain, in varying proportions, of the same 20 L α-amino acids. The kinds of amino acids, the order in which they are joined together, and their mutual spatial relationship dictate the three - dimensional structures and biologic properties of simpleproteins. In addition to their roles in protein, L-amino acids and their derivatives participate in intracellular functions such as nerve transmission, cell growth, and in the biosynthesis of enzymes, porphyrins, purines, pyrimidines, and urea. L-a amino acids are present in polypeptide antibiotics synthesized by microorganisms.
Some amino acids occur in free or combined states and fulfill important roles in metabolic processes. For example, citrulline, and argninousuccinate participate in the formation of urea; tyrosine in the formation of thyroid hormones, and glutamate in neurotransmitter biosynthesis. About 20 - D-amino acids occur in nature. These include the D-alanine and D-glutamate of certain bacterial cell walls and a variety of D-amino acids in antibiotics. |