I was given the following problem in class, I don't understand the answer my friend insists on being right.
"Given that the N terminus has a pK of 9.l0 and the C terminuns has a pK of 3.5. Estimate the net charge of the polypeptide shown below if it were found in the small intestine at a pH of 8?
Tyr-Asp-Lys-Glu
N terminus +1
Tyr 0
Asp -1
Lys +1
Glu -1
C terminus -1
equals net charge of -1
I say it is a net charge of 0 because Tyr has a net charge of +1 at pH 8. Who is right?