Let's understand the concept of optical activity in amino acids.

Optical activity is the ability of a substance to rotate the plane of plane-polarized light. For a molecule to be optically active, it must be chiral and not possess a plane of symmetry. Chirality most commonly arises from a carbon atom that is bonded to four different groups. This carbon is called a chiral center or a stereocenter.

Now, let's look at the general structure of an $\alpha$-amino acid:

${\mathrm{NH}}_2-\mathrm{CH}-\mathrm{COOH}$

The $\alpha$-carbon is the central carbon atom. For it to be a chiral center, its four substituents must all be different. These substituents are:

1. An amino group ($-{\mathrm{NH}}_2$)
2. A carboxyl group ($-\mathrm{COOH}$)
3. A hydrogen atom ($-H$)
4. An R group (the side chain)

For the $\alpha$-carbon to be chiral, the R group must be different from $-H$, $-{\mathrm{NH}}_2$, and $-\mathrm{COOH}$. In the case of glycine, the R group is simply a hydrogen atom ($-H$). This means the $\alpha$-carbon in glycine has two identical hydrogen atoms bonded to it. Therefore, it is not a chiral center and the molecule is symmetric. As a result, glycine is not optically active.

In all other standard amino acids, the R group is different from H, NH$2_{}$, and COOH, making the $\alpha$-carbon a chiral center. This includes lysine and glutamic acid. Thus, they are all optically active.

Conclusion: The correct statement is that all amino acids except glycine are optically active.

Related Topics & Formulae

Chirality: A molecule is chiral if it is not superimposable on its mirror image. The most common source of chirality is a carbon atom with four different substituents (a chiral center).

General Amino Acid Structure: $H_{2}N-CH\left(R\right)-COOH$

Condition for Optical Inactivity (Achirality): A molecule must have a plane of symmetry to be achiral (optically inactive). Glycine's α-carbon has a plane of symmetry because two of its substituents are identical (H atoms).