Question

At pH _____ histidine is found mainly in form IV of Figure 1.

a) 1
b) 5
c) 7
d) 9

Answer 1

The correct answer is c) 7.

Step-by-step explanation:

The correct answer is c) 7.

At pH 7, histidine is found mainly in form IV, according to Figure 1.

Basic amino acids like histidine have an amine group that can be either protonated or deprotonated depending on the pH of the solution. Histidine has a pKa of 6.04, which means that at pH 7, it is only partially protonated and in its neutral form. At pH below 6.04, histidine would be mostly protonated, and at pH above 6.04, it would be mostly deprotonated.