Polypeptide
A single chain of amino acids linked by peptide bonds, typically containing more than 20 residues. The term polypeptide is often used interchangeably with protein, though proteins may consist of multiple polypeptide chains folded into complex three-dimensional structures.
Technical Context
The distinction between peptide and polypeptide is based on chain length, though the boundary is not universally agreed. Chains of 2-20 amino acids are generally called peptides, while longer chains are polypeptides. When a polypeptide folds into a functional three-dimensional structure (often with multiple domains), it is typically referred to as a protein. Many therapeutic compounds tracked on PeptideTrace — such as somatropin (191 amino acids) and glatiramer acetate (a mixture of polypeptides averaging 40-100 residues) — are technically polypeptides or proteins but are commonly discussed alongside shorter peptides due to shared biological mechanisms.