Of the Following Amino Acids,which Will Have a PI Closest

Question

Of the following amino acids,which will have a pI closest to 3?
A)Cys
B)His
C)Gly
D)Asp
E)Lys

Accepted Answer

Asp (aspartic acid) has a pKa value close to 3, which means it will have a pI closest to 3. The pKa values of the other amino acids are: Cys (8.3 and 10.8), His (6.0 and 7.5), Gly (2.4 and 9.8), and Lys (10.4 and 2.2).