NEET 2026 (Phase 1) · BiologyAmino acids/proteinsPrevious Year Question
Alpha-helix is found in which level of protein structure?
- A.Secondary structure✓
- B.Tertiary structure
- C.Primary structure
- D.Quaternary structure
Correct Answer
(A) Secondary structure
Solution & Explanation
Answer: (A) Secondary structure. Solution: NCERT describes the protein thread as folding into a helix (like a revolving staircase), and states that only some portions adopt this helical arrangement, which constitutes the secondary structure. Only right-handed (alpha) helices are observed. The primary structure is the linear amino-acid sequence, the tertiary structure is the hollow-ball 3-D fold, and the quaternary structure is the arrangement of multiple subunits, so the alpha-helix belongs to the secondary level. NCERT Reference: Ch 9, p.112, line ~14 — "Other regions of the protein thread are folded into other forms in what is called the secondary structure"
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