Question

______ Glycine has pKa values of 2.1 and 9.0. For which pH would it BEST serve as a buffer?

            A. 11

            B. 8.3

            C. 5.5

            D. 3.1

            E. 2.3

11. ______ The net charge of aspartate in a solution at pH 7 is:

            A. -1

            B. -0.5

            C. +0.5

            D. +1

            E. +1.5

Please explain how to work out the problem thanks.

Answer 1

1. 2.3

2 . (-1) is the ans.

Every free amino acid has at least two ionizable functional groups, the amino group and the carboxylic acid group. Some amino acids have ionizable side chains, like aspartate, glutamate, lysine, arginine, histidine, tyrosine, and cysteine. Each ionizable group has a characteristic pKa. This pKa is fairly predictable in aqueous solution, but when the amino acid is part of a larger, folded polypeptide, the pKa value can differ significantly from its solution value. Also, when amino acids are in a polypeptide chain, only the N-terminal and C-terminal residues have that ionizable amino and carboxylate group, because all the rest have been condensed into peptide bonds