JEE Main 2025 · 23 January · evening · Single correct · +4 / −1
The α-Helix and β - Pleated sheet structures of protein are associated with its :
- (a) tertiary structure
- (b) quaternary structure
- (c) primary structure
- (d) secondary structure
Answer and solution
Answer (d) secondary structure
Solution
Chemistry ma’am · 3 steps
Helix and sheet are shapes of the backbone held by hydrogen bonds, and that is the secondary level.
- Four levels. Primary is only the sequence of amino acids. Secondary is how that chain locally folds. Tertiary is the overall 3D shape of one chain. Quaternary is how several chains pack together.
Level What it describes Held by Primary order of amino acids in the chain peptide bonds Secondary α-helix and β-pleated sheet H-bonds between C=O and N-H of the backbone Tertiary overall folding of one chain (fibrous or globular) H-bonds, disulphide links, van der Waals and ionic forces Quaternary arrangement of two or more chains same forces, between the chains - Helix and sheet. In an α-helix the chain coils into a right-handed spiral, with H-bonds within the same chain. In a β-pleated sheet chains lie side by side, with H-bonds between neighbouring chains.
- So. Both shapes come from hydrogen bonding in the peptide backbone, so they belong to the secondary structure, option (d).
The idea to keep. Secondary structure means the regular local shapes of the peptide backbone, held by H-bonds: the α-helix and the β-pleated sheet. Tertiary is the whole chain folding, quaternary is chains packing.
Answer from the NTA final answer key. Solution by PrepWiser.