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DNA strands on a gel stained with ethidium bromide when viewed under UV radiation, appear as:
Pure DNA fragments cannot be seen in visible light without staining! When stained with ethidium bromide (an intercalating fluorophore) and exposed to UV light, DNA fluoresces as intense bright orange bands. Match Option (2)!
Ethidium bromide () is a planar, polycyclic aromatic fluorophore that inserts (intercalates) between stacked hydrophobic nitrogenous base pairs of double-stranded DNA:
Upon intercalation into DNA's hydrophobic interior, EtBr fluorescence increases nearly 20-fold compared to free dye in aqueous solution. When irradiated with UV light, the separated DNA fragments shine distinctly as bright orange bands.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
DNA stained with ethidium bromide does not fluoresce yellow under UV radiation.
Ethidium bromide intercalated in DNA fluoresces with characteristic bright orange light upon UV excitation.
Ethidium bromide solution is reddish in visible light, but its fluorescence emission under UV is bright orange.
Bromophenol blue tracking dye appears blue in visible light, but it does not represent stained DNA under UV.
EtBr liquid looks dark orange/red in daylight, and tracking dyes are blue. Candidates mistakenly select "Dark red" or "Bright blue" instead of "Bright orange".
"The separated DNA fragments can be visualized only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation; you can see bright orange coloured bands of DNA."
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