Proteins are molecules that consist of one or more chains of amino acids. Each different protein has a distinct set of amino acids in a particular order. The primary structure refers to the sequence of the amino acids of a single polypeptide chain from its start (N-terminus) to its end (C-terminus). The amino acids are held together by a specific type of covalent bond, known as a peptide bond, which are made during the process of protein biosynthesis or translation.