Class NEET 2026 ALL Q #1957
KNOWLEDGE BASED
APPLY
4 Marks 2026 NTA-RE-NEET-2026 MCQ SINGLE
The correct statement about peptides and proteins is
(A) In $\alpha$-helices, the polypeptide chain is twisted into a left-handed screw (helix) through intramolecular hydrogen bonds
(B) Tertiary structure of proteins has two or more polypeptide subunits
(C) Only the proteins having a quaternary structure are biologically active
(D) In $\beta$-pleated sheet structures, peptide chains are held together by intermolecular hydrogen bonds
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Correct Answer: D

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Detailed Solution

Step 1: Analyze Option A

In α-helices, the polypeptide chain is twisted into a right-handed screw (helix), not left-handed. Therefore, this statement is incorrect.

Step 2: Analyze Option B

The tertiary structure refers to the overall folding of a single polypeptide chain. The presence of two or more polypeptide subunits refers to the quaternary structure. Therefore, this statement is incorrect.

Step 3: Analyze Option C

Many proteins are biologically active in their primary, secondary, or tertiary structures (e.g., enzymes like myoglobin have tertiary structure). Quaternary structure is not a prerequisite for biological activity. Therefore, this statement is incorrect.

Step 4: Analyze Option D

In β-pleated sheet structures, all peptide chains are stretched out to nearly maximum extension and then laid side by side, which are held together by intermolecular hydrogen bonds. This statement is scientifically accurate.

Final Answer: D

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student must apply their knowledge of protein structural biology to evaluate the validity of four distinct biological statements.
Knowledge Dimension: CONCEPTUAL
Justification: The question tests the understanding of structural hierarchies (primary to quaternary) and bonding patterns in biomolecules.
Syllabus Audit: In the context of NEET, this is classified as KNOWLEDGE. This question directly assesses the core concepts of the Biomolecules chapter as per the NCERT curriculum.

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