Histidine has pKa values of 1.8,6.0 (R-group)and 9.3.At pH 8.0,the net charge on histidine is
A)positive.
B)negative.
C)neutral (uncharged).
D)Insufficient information to tell.

Question

Quizplus · Accepted Answer

At pH 8.0, the protonated form of histidine (with a positive charge) will be deprotonated (neutral charge) due to the pH being higher than the pKa values of both the R-group and the amino group. However, the side chain carboxyl group with a pKa of 1.8 will still be protonated (positive charge), making the overall charge of histidine neutral (uncharged).

Histidine Has PKa Values of 1