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organic compound composed of amino acids linked together chemically by peptide bonds. The peptide bond always involves a single covalent link between the α-carboxyl (oxygen-bearing carbon) of one amino acid and the amino nitrogen of a second amino acid.
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an organic compound containing six to 80–90 amino acid residues; the upper limit corresponds to a molecular weight of about 10,000. Such polypeptides, unlike proteins, can pass through semipermeable membranes.
The simple polypeptides are crystalline substances that are readily soluble in water and have chemical properties similar to those of amino acids. The complex polypeptides are amorphous and react with water to yield colloidal solutions. Polypeptides are formed in the organism during enzymatic proteolysis (autolysis of tissue, digestion, and so on) and during biosynthesis from amino acids. Many natural polypeptides exhibit the biological activity of hormones, antibiotics, and toxins. Synthetic polypeptides serve as models in studying the structure and biological activity of proteins.