Glycine and alanine are different with respect to one substituent on the $\alpha$-carbon. What are the other common substituent groups?

(N/A) The general structure of an amino acid consists of an $\alpha$-carbon atom bonded to four different groups: a hydrogen atom $(H)$,an amino group $(-NH_{2})$,a carboxyl group $(-COOH)$,and a variable $R$-group.
In both glycine and alanine,the common substituent groups attached to the $\alpha$-carbon are the hydrogen atom $(H)$,the amino group $(-NH_{2})$,and the carboxyl group $(-COOH)$.