3. Depicted below is the general structure of the amino acid histidine, which has three pka values: 1.82 (COOH), 6.00 (the imidazole ring), and 9.17 (Amino group). The pI (isoelectric point) of Histidine is 7.59. pI is the pH where the amino acid has no net charge. It is the pH at which the concentration of zwitterion is a max. Draw the structures of Histidine that will predominantly exist at the given pH. Please refer to the latter half of the Nov. 19th lecture (1 hour and 9 minute mark) regarding pl. ) H 3 4 b) pH = pl ) H %3D 12 O OH H2N -H NH