See image — Biomolecules Chemistry Question

💡 Solution & Explanation

Concept: The isoelectric point (pI) of an amino acid is the pH at which the molecule carries no net electrical charge. The pI depends on the nature of the side chain (R group). Reasoning: - Neutral amino acids (no ionizable side chain): Glycine (pI ≈ 5.97) and Alanine (pI ≈ 6.00) have pI values near neutral pH because their only ionizable groups are the α-amino and α-carboxyl groups. - Acidic amino acids (extra carboxyl group in side chain): Aspartic acid has two carboxyl groups and one amino group. The extra acidic side chain lowers the overall pI significantly. The pI of Aspartic acid ≈ 2.77, which is the lowest among the options. - Basic amino acids (extra amino group in side chain): Lysine has an extra amino group in its side chain, which raises its pI above neutral (pI ≈ 9.74), giving it the highest pI among the options. Why other options fail: - Glycine (pI ≈ 5.97): neutral amino acid, pI near 6, not the lowest. - Alanine (pI ≈ 6.00): neutral amino acid, pI near 6, not the lowest. - Lysine (pI ≈ 9.74): basic amino acid, has the highest pI among these options. Aspartic acid, being an acidic amino acid with an additional carboxyl group in the side chain, has the lowest isoelectric point (~2.77) among the given choices. Therefore, the correct answer is C.