With the exception of glycine, all other a-amino acids have chiral carbon atom therefore glycine is achiral a-amino acid. $ \underset{glycine}{\mathop{N{{H}_{2}}-\underset{\begin{smallmatrix} | \\ H \end{smallmatrix}}{\overset{\begin{smallmatrix} H \\ | \end{smallmatrix}}{\mathop{C}}}\,-COOH}}\, $