Identifying dipolar ions

There is a question in my textbook that reads P-amino acid is not a dipolar ion, whereas glycine (aminoacetic acid) is not a dipolar ion- how do you account for this? I understand that there may be some ring stability involved with the amino bezoic acid but I know that if aqueous acid is added than they will both be converted to a dipolar ion or will they? Need help with distiguishing.