Question

At pH 7, how many charged groups are present in the pentapeptide ADHSK?

a) 0
b) 1
c) 2
d) 3

Answer 1

The pentapeptide ADHSK at pH 7 has 3 charged groups - 1 negatively charged carboxyl group, 1 positively charged amino group from Histidine, and 2 positively charged amino groups from Lysine.

Step-by-step explanation:

The pentapeptide ADHSK contains the amino acids Alanine (A), Aspartic acid (D), Histidine (H), Serine (S), and Lysine (K). At pH 7, all amino acids in a peptide are partially charged. In the case of ADHSK, Alanine and Serine have no charged groups. Aspartic acid has 1 negatively charged carboxyl group, Histidine has 1 positively charged amino group, and Lysine has 2 positively charged amino groups. Therefore, at pH 7, there are a total of 3 charged groups present in the pentapeptide ADHSK.