All of the Amino Acids EXCEPT ____ Have Both Free

Question

All of the amino acids EXCEPT ____ have both free α-amino and free α-carboxyl groups.
A) aspartic acid
B) proline
C) asparagine
D) lysine
E) valine

Accepted Answer

Proline is unique because it forms a cyclic structure that does not have a free α-amino group. All of the other amino acids have both a free α-amino and free α-carboxyl group.