Q.24 Which of the following methods are used for detection of DNA and RNA,
respectively?
(A) Southern and Northern blotting
(B) Southern and Western blotting
(C) Northern and Southern blotting
(D) Northern and Western blotting
Correct Answer: (A) Southern and Northern blotting
Southern blotting detects specific DNA sequences, while Northern blotting identifies specific RNA sequences, making option (A) the accurate choice for DNA and RNA detection, respectively.
Option Analysis
Option (A): Southern blotting involves DNA restriction digestion, gel electrophoresis, transfer to a membrane, and hybridization with a labeled DNA probe for specific DNA detection. Northern blotting uses similar steps but for RNA, denaturing it to separate fragments and detect gene expression via RNA probes. This matches DNA-RNA detection perfectly.
Option (B): Pairs Southern (DNA) with Western blotting, which detects proteins using antibodies after SDS-PAGE separation, not RNA. Incorrect for RNA.
Option (C): Reverses the order—Northern (RNA) first, then Southern (DNA)—but the question specifies DNA then RNA.
Option (D): Northern (RNA) with Western (proteins), failing for DNA detection.
Introduction
Master Southern and Northern blotting techniques for precise DNA and RNA detection in molecular biology. These methods, essential for IIT JAM and NEET exam prep, involve gel electrophoresis, membrane transfer, and probe hybridization to identify nucleic acids—key for gene analysis and diagnostics.
Blotting Techniques Overview
Blotting detects biomolecules post-separation:
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Southern Blotting (DNA): Digests DNA with restriction enzymes, runs agarose gel, transfers to nitrocellulose/nylon membrane, denatures, and hybridizes with labeled probe for specific sequences like mutations or fingerprints.
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Northern Blotting (RNA): Separates RNA on denaturing gels (formaldehyde), transfers, and probes for mRNA expression levels, aiding gene regulation studies.
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Western Blotting (Proteins): Denatures proteins via SDS-PAGE, transfers, and uses antibodies—not for nucleic acids.
| Technique | Target | Separation | Detection | Key Use |
|---|---|---|---|---|
| Southern | DNA | Agarose gel | DNA/RNA probe | Gene mapping, mutations |
| Northern | RNA | Denaturing gel | RNA probe | Expression analysis |
| Western | Protein | SDS-PAGE | Antibodies | Protein ID |
Applications in Exams and Research
These techniques appear in competitive exams for distinguishing biomolecules. Southern aids forensics and prenatal diagnostics; Northern tracks RNA in diseases. Practice identifies correct pairings like option (A).
