Question

Identify the correct statements.

• Arginine and Tryptophan are essential amino acids.
• Histidine does not contain heterocyclic ring in its structure.
• Proline is a six membered cyclic ring amino acid.
• Glycine does not have chiral centre.
• Cysteine has characteristic feature of side chain as \( \mathrm{MeS-CH_2-CH_2-} \)

• A. C and E Only
• B. B and E Only
• C. C and D Only
• D. A and D Only

Hint:

Remember:

• Glycine is the only achiral amino acid.
• Proline has a five-membered ring.
• Histidine contains an imidazole ring.
• Methionine contains sulfur in thioether form.

Answer 1

The Correct Option is D

Concept: Amino acids are classified based on their structure, side chain and nutritional importance.

• Essential amino acids cannot be synthesized by the human body.
• Glycine is achiral because it contains two hydrogen atoms attached to the \(\alpha\)-carbon.
• Histidine contains an imidazole heterocyclic ring.
• Proline contains a five-membered cyclic ring.

Step 1: Check statement A Arginine and Tryptophan are considered essential amino acids. Hence statement A is correct.

Step 2: Check statement B Histidine contains an imidazole ring which is heterocyclic. Hence statement B is incorrect.

Step 3: Check statement C Proline contains a five-membered cyclic ring and not a six-membered ring. Hence statement C is incorrect.

Step 4: Check statement D Glycine has structure \( \mathrm{NH_2-CH_2-COOH} \). Since the central carbon contains two hydrogen atoms, it is achiral. Hence statement D is correct.

Step 5: Check statement E The side chain \( \mathrm{MeS-CH_2-CH_2-} \) belongs to Methionine and not Cysteine. Hence statement E is incorrect. Therefore, the correct statements are A and D only.