What is a peptide, and how is it different from a protein?

A peptide is a chain of amino acids linked by peptide bonds. There is no single agreed cutoff, but peptides are generally understood as shorter chains — roughly 2 to 50 amino acids — while proteins are longer chains that typically fold into a defined, stable three-dimensional structure. The distinction is one of scale and structure, not of chemistry: a protein is, in a sense, a very long peptide that has folded into a functional shape.

A peptide’s “sequence” is the specific order of its amino acids, read from one end (the N-terminus) to the other (the C-terminus). That sequence, together with the molecule’s molecular weight — the mass of one molecule, typically reported in daltons — is what an identity test is actually confirming when a lot record states an “identity result.”

Not every research compound in a catalog like this one is necessarily a peptide; the term “research compound” is broader. Each compound’s own hub article states its actual molecular class.