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Upon exposure to UV radiation, DNA stained with ethidium bromide will show
DNA cannot be seen directly in visible light. Staining with ethidium bromide followed by UV light transillumination yields striking bright orange bands!
Ethidium bromide () is a planar polycyclic aromatic cation that slips between adjacent stacked nitrogenous base pairs of double-stranded DNA:
Intercalation isolates the ethidium fluorophore from water molecules that would otherwise quench its fluorescence. When irradiated with UV light, the complex emits intense visible fluorescence:
The separated orange DNA bands are excised from the agarose gel slab and extracted into buffer in a technique known as elution.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
Matches NCERT verbatim: DNA stained with ethidium bromide glows as bright orange bands under UV transillumination.
Incorrect hue; emission is distinctly bright orange, not red.
Blue color corresponds to tracking dye (bromophenol blue) under visible light, not fluorescent DNA.
Incorrect emission wavelength.
Students forget that DNA bands cannot be seen under ordinary visible light without UV transillumination, or confuse the blue loading dye with the intercalating stain.
"You cannot see pure DNA fragments in the visible light and without staining. 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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