1. Primary structure :

The sequence of the different amino acids constitutes the primary structure of the peptide or protein. Counting of residues always starts at the N-terminal end (NH₂-group), which is the end where the amino group is not involved in a peptide bond. The primary structure of a protein encodes its uniquely folded 3D conformation. The most important factor governing the folding of a protein into 3D structure is the distribution of polar and non-polar side chains. Folding is driven by the burial of hydrophobic side chains into the interior of the molecule so as to avoid contact with the aqueous environment.