Glycine is the simplest amino acid and is the only amino acid that is not optically active (it has no stereoisomers).

Why is glycine is not optically active?

Complete answer: Glycine is the only chiral amino acid with a single hydrogen atom as its side chain. The absence of asymmetric carbon atoms makes glycine optically inactive that means glycine does not rotate the plane polarised light.

Why glycine is optically active?

Glycine is a nonpolar amino acid. It is the simplest of the 20 natural amino acids; its side chain is a hydrogen atom. Because there is a second hydrogen atom at the ± carbon, glycine is not optically active. Since glycine has such a small side chain, it can fit into many places where no other amino acid can.