Polypeptide
Also known as: long peptide · oligopeptide chain
A longer chain of amino acids (typically 50+ residues) that may or may not fold into a functional protein structure.
The boundary between peptide and polypeptide is conventional rather than strict — 50 residues is a common cutoff but 40 or 100 have both been proposed. Polypeptides include many hormones at the larger end (insulin is 51 residues, close to the boundary) and smaller functional proteins.
For research purposes, the key practical distinction is manufacturing difficulty. Short peptides (10–30 residues) synthesize cleanly; polypeptides above ~50 residues are harder to produce at high purity and more prone to misfolding, batch variance, and higher production cost. This is visible in sourcing: short-chain compounds are abundant and cheap; polypeptides are rarer and more expensive per mg.
Related Terms
Peptide
A short chain of amino acids linked by peptide bonds, typically fewer than 50 residues, functioning as a signaling molecule in biological systems.
Batch Variance
The observed variability in purity, potency, or mass accuracy between different production lots of the same peptide from the same vendor.
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