?

Walter continued with his experiments, making a tetrapeptide made up of four new amino acids that have the following R groups: OH SH thiophenol pk = 6.6 hydroxycyclohexene pk = 11.0 NH cyclohexanamine pk = 10.6 pyridine pk = 5.2 Assume that in Walter's tetrapeptide the pK, of the alpha-amino group is 9.0, that of the alpha- carboxylic is 2.0, and those of the R groups are the same as in the free molecules. a) what is the charge on the tetrapeptide when all ionizable groups are fully protonated? b) what is the charge on the tetrapeptide when all ionizable groups are fully deprotonated? c) determine isoelectric point of tetrapeptide