Both temperature and pH can change polypeptide shape. When such proteins lose their normal configuration, the protein is denatured. Once a protein loses its normal shape, it cannot perform its usual function. The sequence of amino acids, therefore, forecasts the protein's final shape. Final 3-D shape of a protein determines function of the protein in the organism.
Primary structure is sequence of amino acids joined by peptide bonds.
First broke insulin into fragments and determined amino acid sequence of fragments. Since amino acids differ by R group, proteins differ by a particular sequence of the R groups. Secondary structure results when a polypeptide takes a particular shape. Hydrogen bonding between every fourth amino acid holds spiral shape of an a helix. The sheet was the second pattern discovered.