JEE Main 2018 — Biomolecules Question with Solution
From: JEE Main 2018 (Offline)
Question
The predominant form of histamine present in human blood is (pKa, Histidine = 6.0)
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Show full solutionCorrect option: A
Correct answer
A
Step-by-step explanation
Blood is slightly basic in nature as it's pH is around 7.4 .
In Histamine there is two basic centers
(1) Aliphatie amino group
(2) Basic nitrogen of imidazole ring.
Where pKa of Aliphatic amino group is 9.4 and pKa of basic nitrogen of imidazole ring is 5.8.
As more pKa value means more basic, So, aliphatic amino group is more basic.
As pH of blood is 7.4 so pKa of blood is < 7.4. So, NH2 group will act as more basic compare to blood. So, blood will act as acid and donate H+ to NH2 group.
So, Histamine in blood will become this :
In Histamine there is two basic centers
(1) Aliphatie amino group
(2) Basic nitrogen of imidazole ring.
Where pKa of Aliphatic amino group is 9.4 and pKa of basic nitrogen of imidazole ring is 5.8.
As more pKa value means more basic, So, aliphatic amino group is more basic.
As pH of blood is 7.4 so pKa of blood is < 7.4. So, NH2 group will act as more basic compare to blood. So, blood will act as acid and donate H+ to NH2 group.
So, Histamine in blood will become this :
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This is a previous-year question from JEE Main 2018, covering the Biomolecules chapter of Chemistry. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.