A peptide is a chain of amino acids joined by peptide bonds, conventionally between 2 and about 50 residues. Above roughly 50 residues the same kind of molecule is usually called a protein, but that boundary is a naming convention rather than a chemical rule. Nearly everything in a research peptide catalog sits well under the line: GHK-Cu and KPV are tripeptides, BPC-157 is a 15-residue pentadecapeptide, and semaglutide is a 31-residue GLP-1 analog carrying a fatty-acid side chain.
How chain length shapes research material
Length drives how material is made and what its paperwork should show. Short and mid-length sequences are assembled by solid-phase peptide synthesis, one residue at a time from the C-terminus; longer or glycosylated molecules are typically recombinant. The route determines the impurity profile a laboratory sees — deletion sequences, incomplete deprotection, oxidised residues — and the counter-ion (usually acetate or trifluoroacetate) that arrives with the powder.
Why it matters
The word "peptide" on a vial says nothing about identity, net peptide content, or salt load. Two vials naming the same sequence can differ in modification state (amidation, acetylation) and in impurity spectrum. Confirmation comes from HPLC purity plus a mass spectrometry mass match, reported against the specific lot on a certificate of analysis. All material is supplied research use only.
Related terms
amino acid · peptide bond · purity. Browse all research peptides or start with BPC-157.