When a protein in its native form, is subjected to physical or chemical change, then its
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Only the primary structure remains intact.
Denaturation breaks only the weak hydrogen bonds; the covalent peptide bonds are not broken, so the sequence of amino acids, the primary structure, survives.
Why the other options are incorrect
Option (1) The primary and secondary structures remain intact. — Incorrect. The secondary structure (α-helix, β-pleated sheet) is held by hydrogen bonds, which denaturation breaks.
Option (2) The secondary and tertiary structures remain intact. — Incorrect. These are the very structures that are lost on denaturation.
Option (3) Only the secondary structure remains intact. — Incorrect. The secondary structure is destroyed, while the primary structure survives.
NCERT (2026-27 edition):
Denaturation of Proteins
