A polypeptide is a chain of amino acids linked by peptide bonds. It is a polymer that forms during protein synthesis and can vary in length, typically consisting of 50 or more amino acids. Polypeptides fold into specific three-dimensional shapes, which are crucial for the functional properties of the resulting proteins. The sequence of amino acids in a polypeptide determines its structure and function, making it central to biological processes such as enzyme activity and cell signaling.