How it works
Amino acids join by peptide bonds — amide links formed between one residue’s carboxyl group and the next’s amine — to make a chain with a defined direction, from an N-terminus to a C-terminus. The order of residues is the sequence, and it is what distinguishes one peptide from another.
The twenty standard amino acids are only the starting set. Research peptides frequently include non-standard residues (norleucine, D-amino acids), terminal modifications (N-acetylation, C-terminal amidation), cyclisation (a lactam bridge), or attached groups (acylation, metal coordination) — all compositional facts a full characterization records.
Length shades into protein territory without a hard boundary. What matters for characterization is not the label but the sequence and modifications, because those determine the formula, the mass, and how the molecule behaves in an assay.
Why it matters
Peptides are defined by sequence, so identity work is sequence-anchored: the formula and mass follow from the residues and their modifications, and a structure is derived from the sequence rather than guessed.
The prevalence of modifications is why characterization is careful. A single substituted residue or a changed terminus alters the formula and mass in a defined way, and the difference between two similar peptides can be one residue.
Because a peptide’s behavior in HPLC and mass spectrometry depends on its sequence and size, the same analytical methods are tuned per molecule — a recurring theme across the compound pages.
At Lineará
The compound pages draw each peptide’s sequence residue-by-residue and list its modifications, with the formula and mass that follow from them.
Where a peptide’s structure warrants it, the sequence chain shows terminal chemistry, non-standard residues, bridges, and coordination — the compositional detail that distinguishes one peptide from a near neighbour.