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GATE 2024 BT Q.26: solution and answer

GATE 2024 · BTQ.26 · 1 mark · MCQ

If a denatured protein of human origin is injected into a rabbit, antibodies generated will recognize the ________ structure of the protein.

  1. (A)

    primary

  2. (B)

    secondary

  3. (C)

    tertiary

  4. (D)

    quaternary

See the question in the paper
GATE 2024 BT question 26Tap to open full size

Answer and solution

ANSWER

The antibodies recognize the primary structure of the protein, option (A).

Official answer: ASource: Official answer key, GATE 2024 BT (IISc Bengaluru)

  1. Antibodies bind epitopes. On a native (folded) protein, most B-cell epitopes are conformational: they are formed by the folded tertiary structure, with residues far apart in the sequence brought together.

  2. Denaturation (heat, urea, detergent) destroys the quaternary and tertiary structure and most of the secondary structure, leaving an unfolded polypeptide chain. Only the covalent peptide bonds survive, so the amino-acid sequence (primary structure) is the one level of structure that remains intact.

  3. The injected denatured protein therefore presents mainly linear epitopes, short stretches of consecutive amino acids. The B cells that respond, and the antibodies they make, are directed against these sequence stretches.

  4. Option (B) secondary: helices and sheets are largely lost on denaturation, so they are not what the immune system sees. Option (C) tertiary: the fold is lost, so conformational epitopes no longer exist. Option (D) quaternary: subunit assembly is lost.

  5. Hence the antibodies recognize the primary structure: option (A).

KEY IDEA

A denatured protein has lost its folded shape but keeps its amino-acid sequence, so antibodies raised against it bind linear epitopes made of consecutive residues, that is, primary structure.

WATCH OUT FOR

Choosing tertiary because antibodies usually recognize the folded shape of a native protein. That applies to conformational epitopes, which are destroyed here.

From the GATE 2024 BT paper. Every question of this paper · Download the full paper · All 6 Immune system questions, with notes

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