Concept:Essential amino acids cannot be synthesized by the body. Glycine has no chiral carbon due to two identical H atoms.
Explanation:Statement A: Arginine and tryptophan are essential amino acids. This is correct.
Statement B: Histidine contains an imidazole heterocyclic ring, so it is incorrect.
Statement C: Proline has a five‑membered pyrrolidine ring, not six‑membered, so it is incorrect.
Statement D: Glycine has
−CH2​− with two H atoms, no chiral centre. This is correct.
Statement E: Cysteine side chain is
−CH2​SH, not
−SCH2​CH2​− (which is methionine), so it is incorrect.
Answer:B. A and D Only
