What is the net charge of an amino acid (possessing two pKA values) at the isoelectric pH? A. 0.5 B. 1 C. 0 D. -1

The net charge of an amino acid at its isoelectric pH is 0 (Option C).

Here's why:

The isoelectric point (pI) is the pH at which a particular molecule or surface carries no net electrical charge.

Amino acids, which are the building blocks of proteins, have both a basic (amine) and an acidic (carboxyl) group. At any given pH, an amino acid may exist in one of three forms:

1. A positively charged form (NH3+ CH(R) COOH)
2. A neutral, zwitterionic form (NH3+ CH(R) COO-)
3. A negatively charged form (NH2 CH(R) COO-)

At the isoelectric pH, the amino acid exists primarily in the zwitterionic form, which carries no net electrical charge. Therefore, the net charge of an amino acid at the isoelectric pH is 0.