The sequence of amino acid, the positional information in protein, which is first amino acid and which is second and so on is called the primary structure. Amino acids are joined by peptide bond formed between COOH group of first amino acid and ${\mathrm{N}\mathrm{H}}_2$ group of second amino acid. Thus the first amino acid is left end, has free ${\mathrm{N}\mathrm{H}}_2$ group known as N Terminal amino acid and last amino acid is right end has free COOH group thus known as C Terminal amino acid.