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JEE Main 2025 Apr 2 Shift 1, Chemistry Q12: Proteins

JEE Main2025Apr 2, Shift 1Chemistry
Q.

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.

Solution

Evaluating each option:

(1) False. Isoleucine and threonine each contain two chiral centres, so the claim that every non-glycine amino acid has exactly one is wrong.

(2) False. Glycine, with two hydrogens on the -carbon, is achiral and optically inactive.

(3) False. Aspartic acid also bears a –COOH side chain, so glutamic acid is not the only one.

(4) True. Cysteine carries a free –SH group, and two cysteine residues oxidise readily to form a disulfide-linked dimer (cystine). This is the basis of disulfide bridges in proteins.

Option (4) is correct.

Concept behind this question

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