After a polypeptide chain has been synthesized, certain amino acids in the peptide may become modified. for each modified amino acid, identify the standard amino acid from which it is derived. enter the unabbreviated name of the standard amino acid. the amino acid structure shows the fully ionized form. the side chain is c h 2, c h 2, c h (o h), c h 2, n h 3 (plus). standard amino acid: identify the modification that yields the first amino acid depicted.