Amino acid sequence
The ordered list of amino acids in a peptide, written N-terminus to C-terminus.
A peptide's amino acid sequence is the ordered list of its constituent amino acids, written by convention from N-terminus (free amino group) to C-terminus (free carboxyl group). Standard one-letter codes (A=Ala, V=Val, etc.) are used for compact notation; three-letter codes (Ala, Val) for clarity. For example, oxytocin's sequence is CYIQNCPLG (9 aa). The sequence determines the peptide's primary structure; secondary structure (alpha-helices, beta-sheets) and tertiary structure (3D fold) emerge from the sequence-driven physicochemical interactions. A peptide's identity in a research COA is confirmed via mass spectrometry against the theoretical mass calculated from the sequence.