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

Step 1: Understanding the Concept:
This question evaluates fundamental structural, stereochemical, and nutritional classifications of standard amino acids which serve as the building blocks of proteins.
Step 2: Detailed Explanation:
Let us evaluate each individual statement for structural correctness: - Statement A: Essential amino acids cannot be manufactured natively by the human body and must be supplied directly through food intake. Both Arginine and Tryptophan are classified as essential amino acids (Arginine is semi-essential, required during growth phases). Thus, Statement A is correct. - Statement B: Histidine contains a side chain consisting of an imidazole ring system. An imidazole ring contains carbon and nitrogen atoms within the cycle, making it a classic heterocyclic ring. Thus, Statement B is incorrect. - Statement C: Proline is unique because its side chain cyclizes back onto its own secondary amine nitrogen atom, forming a pyrrolidine ring system. This ring system contains 4 carbon atoms and 1 nitrogen atom, making it a five-membered ring, not six-membered. Thus, Statement C is incorrect. - Statement D: A carbon atom is a chiral center if it is bound to four entirely distinct functional groups. The $\alpha$-carbon of Glycine ($\text{H}_2\text{N}-\text{CH}_2-\text{COOH}$) is bonded to an amino group ($-\text{NH}_2$), a carboxylic acid group ($-\text{COOH}$), and two identical hydrogen atoms ($-\text{H}$). Because it contains two identical attachments, it is achiral and lacks a chiral center. Thus, Statement D is correct. - Statement E: Cysteine features a thiol group in its side chain, represented structurally as $-\text{CH}_2-\text{SH}$. The structural side chain pattern mentioned in the statement ($\text{CH}_3-\text{S}-\text{CH}_2-\text{CH}_2-$ or $\text{MeS}-\text{CH}_2-\text{CH}_2-$) belongs to Methionine, another sulfur-containing amino acid. Thus, Statement E is incorrect. Reviewing our verified findings, only statements A and D are chemically sound.
Step 3: Final Answer:
The correct option is (D) which includes A and D Only.