Q.26 If a denatured protein of human origin is injected into a rabbit, antibodies generated
will recognize the ________ structure of the protein.
(A) primary
(B) secondary
(C) tertiary
(D) quaternary

Denatured proteins lose higher-order structures but retain their amino acid sequence, allowing antibodies to target the primary structure when injected across species. The correct answer is (A) primary.

Correct Answer

(A) primary

Denaturation disrupts non-covalent interactions, leaving the covalent peptide bonds of the primary structure intact. Rabbits generate antibodies against this exposed linear sequence from the human protein, as higher structures are unfolded. This principle applies in immunology for producing polyclonal antibodies via denatured antigens.​

Primary Structure

Primary structure is the linear sequence of amino acids linked by peptide bonds. Denaturation agents like heat or urea break hydrogen bonds, hydrophobic interactions, and disulfide bridges but spare these strong covalent bonds. Antibodies recognize this unchanged sequence as foreign in rabbits.​

Secondary Structure

Secondary structure involves local folding patterns like alpha-helices and beta-sheets stabilized by hydrogen bonds. These bonds disrupt during denaturation, converting structures to random coils. Antibodies cannot target these lost conformations effectively.​

Tertiary Structure

Tertiary structure is the overall 3D fold from interactions among side chains, including disulfide bonds and van der Waals forces. Denaturation unfolds this by breaking these weak interactions. Native tertiary epitopes vanish, so antibodies focus on primary sequence.​

Quaternary Structure

Quaternary structure assembles multiple polypeptide subunits via non-covalent bonds. Denaturation dissociates subunits and disrupts their arrangement. Multi-subunit proteins lose this level entirely, irrelevant for antibody recognition post-denaturation.​