An unknown amino acid possesses a strongly basic side-chain amino group. Its acid dissociation const — Biomolecules Chemistry Question
Question
An unknown amino acid possesses a strongly basic side-chain amino group. Its acid dissociation constants are: $pKa_1 (\alpha-COOH) = 2.2$, $pKa_2 (\alpha-NH_3^+) = 9.0$, and $pKa_3 (\text{side-chain } NH_3^+) = 10.5$. Calculate the exact isoelectric point (pI) of this specific amino acid.
Answer: C
💡 Solution & Explanation
For basic amino acids possessing an extra ionizable amino group (like Lysine), the isoelectric point ($pI$) is the arithmetic mean of the two highest basic $pKa$ values (the ones bracketing the neutral zwitterion state). $pI = \frac{9.0 + 10.5}{2} = 9.75$.
💬Ask on WhatsApp →
Still have doubts about this question?
Send it to our AI chemistry tutor on WhatsApp — gets answered in minutes