21. Which one of the following chemicals is a DNA intercalator?
(1) 5-Bromouracil
(2) Ethyl methane sulfonate
(3) Acridine orange
(4) UV
Acridine orange is the correct DNA intercalator among the options, as it inserts between DNA base pairs, causing frameshift mutations by altering the helix structure during replication.
Option Analysis
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5-Bromouracil (Option 1): Acts as a thymine analog that incorporates into DNA and tautomerizes to pair with guanine instead of adenine, inducing transition mutations (AT to GC), not intercalation.
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Ethyl methane sulfonate (Option 2): An alkylating agent that adds ethyl groups to DNA bases like guanine, leading to mispairing and point mutations, without inserting between base pairs.
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Acridine orange (Option 3): A classic intercalator with a planar acridine ring that slips between DNA base pairs, unwinding the helix and causing insertions/deletions (frameshifts).
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UV (Option 4): Physical radiation causing pyrimidine dimers (e.g., thymine dimers) that distort DNA and trigger repair errors or mutations, not chemical intercalation.
Intercalation Mechanism
DNA intercalators like acridine orange bind non-covalently by stacking their flat aromatic rings parallel between base pairs, increasing contour length and inhibiting processes like replication and transcription. This binding is reversible and fluorescent under UV, aiding visualization, but mutagenic due to replication slippage. In CSIR NET context, distinguishes from base analogs or alkylators by mode of action.
Exam Relevance
This question tests mutagenesis classification: intercalators (frameshifts) vs base analogs (transitions) vs alkylators (points) vs radiation (dimers). Correct choice (3) Acridine orange aligns with standard textbooks; others mislead as mutagens but not intercalators. Practice identifies via structure and mutation type for competitive exams like CSIR NET Life Sciences.
