What is the overall net charge on the peptide lys-lys-ser-glu at pH 7.0?
A) +2
B) +1
C) 0
D) −1
E) −2

Question

Quizplus · Accepted Answer

At pH 7.0, the lysine residue (pKa = 10.8) and the N-terminus (pKa = 8.0) are fully protonated, giving them a positive charge of +2 (2 amino groups). The glutamic acid residue (pKa = 4.2) is fully deprotonated, giving it a negative charge of -1 (1 carboxyl group). The serine residue (pKa = 13.0) is not charged at pH 7.0 since its pKa is above the pH range. Thus, the overall net charge of the peptide is +1 (2+0-1).

What Is the Overall Net Charge on the Peptide Lys-Lys-Ser-Glu