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. Tertiary structure results when proteins of secondary structure are folded, due to various interactions between the R groups of their constituent amino acids. Quaternary structure results when two or more polypeptides combine. Hemoglobin is globular protein with a quaternary structure of four polypeptides.