Amino acid which is optically ine ?
**Core Concept**
Optical isomerism in amino acids refers to the presence of non-superimposable mirror images, which can have different physical and chemical properties. This phenomenon arises from the presence of a chiral center, typically a carbon atom bonded to four different groups (R-group, carboxyl group, amino group, and hydrogen atom).
**Why the Correct Answer is Right**
The correct answer is a non-essential, branched-chain amino acid that lacks a chiral center due to the presence of two identical groups attached to the alpha carbon atom. This results in a molecule that is not optically active, meaning it does not rotate plane-polarized light. The correct answer is **Glycine**, which has a single hydrogen atom as its R-group, making it the only amino acid without a chiral center.
**Why Each Wrong Option is Incorrect**
* **Option A:** Alanine is an essential amino acid with a chiral center, making it optically active.
* **Option B:** Valine is a branched-chain amino acid with a chiral center, which makes it optically active.
* **Option C:** Leucine is another branched-chain amino acid with a chiral center, resulting in optical activity.
**Clinical Pearl / High-Yield Fact**
Remember that Glycine is the only amino acid without a chiral center, making it optically inactive. This is an important distinction in the context of amino acid metabolism and the synthesis of amino acid derivatives.
**Correct Answer: D. Glycine**