What is the isoelectric point of cysteine? (pK1 = 1.96, pK2 = 8.18 and pK3 = 10.28).

Question

Quizplus · Accepted Answer

The isoelectric point (pI) is the pH at which the net electrical charge of the amino acid is zero. This occurs when the number of positive charges (protons) equals the number of negative charges (deprotonated groups). To calculate the pI, take the average of the two pK values closest to the pH at which the net charge is zero. In the case of cysteine, the two closest pK values are pK1 and pK2. Thus, the pI of cysteine can be calculated as (1.96 + 8.18) / 2 = 5.07. Therefore, the correct answer is B.

What Is the Isoelectric Point of Cysteine? (PK1 = 1