Peptide

A short chain of amino acids linked by peptide bonds — too small to be a full protein but large enough to be biologically active.

Why it matters

Peptides span from di- and tripeptides through chains of several dozen amino acids. Above roughly 50–100 residues the molecule is conventionally called a protein. Insulin (51 amino acids) sits near the boundary; melanotan-2 (7 amino acids) is unambiguously a peptide. Functions include hormone signalling, antimicrobial defence, and tissue repair.

In practice

In the research-peptide market, the term covers a heterogeneous group of injectables, oral tablets, and intranasal sprays sold for research use only. Because peptides are typically degraded in the GI tract, most clinically active peptides are administered by injection or mucosal routes.

Common confusion

“Peptide” and “protein” are often used interchangeably. The distinction is one of size and conventional usage rather than chemistry.

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