Structure and Nomenclature of Peptides and Proteins Peptides A peptide consists of short chain of amino acids linked by a peptide (amide) bonds formed between the carboxyl group of one amino acid and the amino group of another with the removal of water molecule. The number of amino-acid molecules present in a peptide is indicated by a prefix: a dipeptide contains two amino acids; a tripeptide containing three amino acids; tetrapeptide containing four amino acids ; an octapeptide, eight ; a polypeptide, many. Polypeptides are formed by long peptide chains containing large numbers of peptide bonds. Polymers of up to 100 amino acids are termed polypeptides and those with more than 100 are generally termed proteins. The amino acid component retaining a free amine group is drawn at the left end (the N-terminus) of the peptide chain, and the amino acid retaining a free carboxylic acid is drawn on the right (the C-terminus). As expected, the free amine and carboxyl
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