Which structure(s) of proteins remain(s) intact during the denaturation process?

Solution & Explanation

\textbf{Answer:} (B) Only the primary structure remains intact during denaturation. \textbf{Solution:} Denaturation disrupts the secondary and tertiary structures of a protein by breaking hydrogen bonds and other non-covalent interactions, causing loss of biological activity. The primary structure — the sequence of amino acids joined by covalent peptide bonds ($-\mathrm{CONH}-$) — is not affected, since peptide bonds are not broken during denaturation. Hence only the primary structure remains intact, giving option B.