Proteins

Concept:
• Essential amino acids cannot be synthesized
• Non-essential amino acids synthesized in body

Step 1: Classify amino acids.

• Proline Non-essential
• Leucine, Valine Essential

Step 2: Select correct option.
Proline is synthesized in the body.

Step 1: Understanding the Concept:
Optical activity in amino acids arises from the presence of a chiral carbon atom (the -carbon).

Step 2: Detailed Explanation:
For an -amino acid, the general structure is H N-CH(R)-COOH. The -carbon is bonded to -NH , -COOH, -H, and the side chain R.
• Glycine: The side chain is just a hydrogen atom (-H). Therefore, the -carbon is bonded to two hydrogen atoms, making it achiral (not a stereocenter). Glycine is optically inactive.
• Alanine (R = -CH ), Valine (R = -CH(CH ) ), Leucine (R = -CH CH(CH ) ), Isoleucine (R = -CH(CH )CH CH ): All have different side chains, so their -carbon is chiral and they are optically active.

Step 3: Final Answer:
Glycine is the optically inactive amino acid.