Question

The only genetically encoded amino acid without a stereoisomer is

• A. Alanine
• B. Tryptophan
• C. Glycine
• D. Proline

Hint:

Glycine is the "simplest" amino acid because its side chain is just a single Hydrogen atom.

Answer 1

The Correct Option is C

Step 1: Concept
Stereoisomers (chiral molecules) exist when a carbon atom is bonded to four different groups, creating a center of asymmetry.

Step 2: Analysis of Glycine
Glycine's structure is $H_{2}N-CH_{2}-COOH$. Its alpha-carbon is bonded to an amino group, a carboxyl group, and two hydrogen atoms.

Step 3: Reasoning
Because two of the four bonded groups are identical (hydrogen), the molecule is achiral and does not have D- or L- forms.

Step 4: Conclusion
Glycine is the only amino acid without a stereoisomer. Final Answer: (C)