During denaturation of proteins which structure of proteins remain intact?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Primary Structure
Proteins are described at four levels:
Primary structure: the sequence of amino acids, held by covalent peptide bonds.
Secondary structure: the α-helix or β-pleated sheet, held by hydrogen bonds between the >C=O and –NH groups of the chain.
Tertiary structure: the further folding of the chain into fibrous or globular shapes, held by hydrogen bonds, disulphide links, van der Waals and electrostatic forces.
Quaternary structure: the arrangement of two or more polypeptide subunits with respect to each other.
Denaturation breaks only the weak forces (mainly hydrogen bonds) that hold the folded shapes; the covalent peptide bonds are not broken. So the secondary and tertiary structures are lost, while the primary structure remains intact.
Why the other options are incorrect
Option (2) Secondary Structure — Incorrect. The α-helix and β-pleated sheet are held by hydrogen bonds, which are the very bonds disturbed in denaturation.
Option (3) Tertiary Structure — Incorrect. The folding of the chain depends on weak forces and is lost when the globules unfold.
Option (4) Quaternary Structure — Incorrect. The subunits are held together by the same kind of weak forces, so this arrangement is also lost.
NCERT (2026-27 edition):
Denaturation of Proteins
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| 26-05 S1 | 02-06 S1 26-05 S2 | – | – | – |