The primary structure of a protein refers to the order of amino acid residues in the polypeptide chain of the protein. The amino acid is an organic molecule that binds to other amino acids by the peptide bond to form a peptide chain. Amino acids in the peptide chain are called residues. Although hundreds of amino acids are found in nature, proteins are made of 20 kinds of amino acids. Based on the properties of the free radicals at the terminus, the ends of the polypeptide chain are referred to as the amino terminus (N-terminus) and the carboxy terminus (C-terminus), respectively. The residue count always starts from the N-terminus. The amino acid sequence is unique to the protein and is the basis for understanding its structure and function. And the sequence can be determined by methods such as Edman degradation and mass spectrometry.
