The primary structure of a protein (or polypeptide) is the order of amino acids on a protein. For a given protein, the amino acid sequence is fixed, as discovered by Frederick Sanger when he determined the primary structure of bovine insulin in 1951.
A polypeptide of amino acids will always fold into the same three-dimensional protein, which demonstrates that the protein's tertiary structure can be directly inferred from its primary structure. However, the exact rules for inferring the three-dimensional shape of a protein (i.e., its tertiary structure) from its primary structure are still unclear.
