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MCQEasyJEE 2023Proteins (Amino Acids, Structure, Denaturation)

JEE Chemistry 2023 Question with Solution

Sulphur (SS)-containing amino acids from the following are:

  • A

    b, c, e

  • B

    a, d

  • C

    a, b, c

  • D

    b, d

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: The amino acids listed are Isoleucine, Cysteine, Lysine, Methionine, and Glutamic acid.

Find: Which among them are sulphur-containing amino acids.

Sulphur-containing amino acids are those that have a sulphur atom in their side chain.

  • Cysteine: Contains a thiol group −SH-SH in its side chain.
  • Methionine: Contains a thioether group −S−-S- in its side chain.

The remaining amino acids, Isoleucine, Lysine, and Glutamic acid, do not contain sulphur in their structures.

Therefore, the sulphur-containing amino acids are b (Cysteine) and d (Methionine). Hence, the correct option is D.

Common mistakes

  • Confusing amino acids with similar-sounding names is a common mistake. Isoleucine and Lysine do not contain sulphur; check the side chain structure instead of relying on the name.

  • Looking only at the main amino acid backbone is incorrect because sulphur-containing classification depends on the side chain. Always inspect the functional group attached to the α\alpha-carbon.

  • Including Glutamic acid by elimination is incorrect. It contains a carboxylic acid side chain, not any sulphur-containing group. Verify the presence of SS explicitly.

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