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JEE Main · 2025 · 02 Apr 2025 · Shift 1 · Biomolecules

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Identify the correct statement among the following:
  1. (A)All naturally occurring amino acids except glycine contain one chiral centre.
  2. (B)All naturally occurring amino acids are optically active.
  3. (C)Glutamic acid is the only amino acid that contains a –COOH group at the side chain.
  4. (D)Amino acid, cysteine easily undergo dimerization due to the presence of free SH group.✓ Correct

Answer: (D)

Solution

Isoleucine and threonine each hold two stereocentres, so not every amino acid except glycine has a single chiral centre; and glycine itself is achiral and optically inactive, which disposes of the first two claims. Aspartic acid as well as glutamic acid carries a carboxyl group in its side chain, so glutamic acid is not unique in that feature. Cysteine, however, bears a free thiol that is readily oxidised, two molecules joining through a disulphide link to give cystine, so cysteine does undergo this dimerisation.

JEE Main · 2025 · 02 Apr 2025 · Shift 1 · Single correct option

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