At its isoelectric point (pI), in what ionic form does an amino acid predominantly exist in aqueous solution?
Answer and explanation
Correct answer: A. Zwitterion with zero net electric charge
- Step 1: Amino acids contain an amino group (-NH2) and a carboxyl group (-COOH). Step 2. At the isoelectric point (pI), the amino group is protonated (-NH3+) and the carboxyl group is deprotonated (-COO-). Step 3. The dipolar molecule has balanced positive and negative charges, resulting in a zwitterion with net charge zero. Answer: Zwitterion with zero net electric charge. Why not the others: In acid (pH < pI) it is a cation; in base (pH > pI) it is an anion.
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