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MCQMediumJEE 2026Proteins (Amino Acids, Structure, Denaturation)

JEE Chemistry 2026 Question with Solution

Identify the correct statements. (Note: Based on options, the question asks to identify INCORRECT statements).

A. Arginine and Tryptophan are essential amino acids.

B. Glycine does not have chiral centre.

C. Proline is a six membered cyclic ring amino acid.

D. Histidine does not contain heterocyclic ring in its structure.

E. Cysteine has characteristic feature of side chain as MeS−CH2−CH2−MeS-CH_2-CH_2-.

  • A

    B and E Only

  • B

    A and D Only

  • C

    C and D Only

  • D

    C and E Only

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: Statements about amino acids are to be checked, and based on the options the task is to identify the incorrect statements.

Find: Which option matches the incorrect statements.

Step 1: Analyze each statement

  • A: Arginine and Tryptophan are classified as essential amino acids. Arginine is semi-essential or essential for children. So this statement is true.
  • B: Glycine has structure NH2−CH2−COOHNH_2-CH_2-COOH. The α\alpha-carbon has two hydrogen atoms, so glycine is achiral. This statement is true.
  • C: Proline contains a pyrrolidine ring, which is a 5-membered ring containing nitrogen, not a six-membered ring. So this statement is false.
  • D: Histidine contains an imidazole ring, which is a heterocyclic aromatic ring. So this statement is false.
  • E: The side chain Me−S−CH2−CH2−Me-S-CH_2-CH_2- belongs to Methionine, not cysteine. Cysteine has side chain HS−CH2−HS-CH_2-. So this statement is false.

Step 2: Compare with the options

The incorrect statements are C, D, and E. However, no option contains all three.

The solution states that among the given options, Option D is selected, corresponding to C and E only.

Conclusion: There is a discrepancy in the question-options set because C, D, and E are all incorrect, but the provided answer key marks D. Therefore, the correct option according to the solution is D.

Statement-by-statement evaluation

Given: A multiple-correct style statement question on amino acids.

Find: The option intended by the source solution.

The hint emphasizes the distinctive structural features:

  • Proline: secondary amine with a 5-membered ring
  • Histidine: contains an imidazole ring
  • Cysteine: contains a thiol group −SH-SH
  • Methionine: contains a thioether side chain −S−CH3-S-CH_3

Using these facts:

  1. Proline is not a six-membered cyclic amino acid, so statement C is incorrect.
  2. Histidine definitely contains a heterocyclic ring, so statement D is incorrect.
  3. Cysteine does not have side chain Me−S−CH2−CH2−Me-S-CH_2-CH_2-; that description matches Methionine, so statement E is incorrect.

Thus, chemically the incorrect set should be C, D, E.

But the provided options only offer pairs, and the source solution explicitly says The Correct Option is D.

Conclusion: The extracted answer must be D, while noting the internal inconsistency that statement D is also chemically incorrect.

Common mistakes

  • Confusing Cysteine with Methionine. Cysteine has a thiol side chain HS−CH2−HS-CH_2-, whereas Methionine has the thioether side chain Me−S−CH2−CH2−Me-S-CH_2-CH_2-. Check the sulfur-containing functional group before deciding.

  • Assuming Proline has a six-membered ring. Proline contains a 5-membered pyrrolidine ring involving the amino nitrogen. Count the atoms in the ring carefully.

  • Forgetting that Histidine contains an imidazole heterocycle. The statement says it does not contain a heterocyclic ring, which is false. Recall the characteristic ring systems of amino acids.

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