The specific order of amino acids in a peptide or protein chain. Just as the order of letters in a word determines its meaning, the sequence of amino acids determines a peptide’s three-dimensional shape, biological activity, and receptor specificity. Change one amino acid and you can create an entirely different molecule—or destroy function altogether.

Sequence is typically written from the N-terminus (amino end) to the C-terminus (carboxyl end) using standard three-letter or one-letter amino acid codes. When researchers describe a peptide as “Ala-Glu-Asp” or “AED,” they are specifying its sequence.