Ethidium bromide serves as the primary dye for visualizing DNA or RNA bands in agarose gels during electrophoresis, a key technique in molecular biology and genetics for GATE Life Sciences preparation. This intercalating agent fluoresces under UV light when bound to nucleic acids, enabling clear band detection.

Question Solution

The correct answer is Ethidium bromide. It is the classic, widely used fluorescent stain for detecting DNA/RNA separated by agarose gel electrophoresis, offering high sensitivity (1-5 ng/band) via intercalation between base pairs.

Option Analysis

• Ethidium borate: Incorrect. No such compound is used in gel staining; borate acts as a buffer in electrophoresis but does not fluoresce or intercalate with nucleic acids.​

• Ethidium oxide: Incorrect. This is not a recognized dye for DNA/RNA visualization; ethidium derivatives like oxide lack the bromide’s established intercalating and fluorescent properties.​

• Ethidium bromide: Correct. Intercalates into dsDNA/RNA, absorbs UV at 300/360 nm, and emits orange light at 590 nm for visualization. Less efficient for ssRNA (10-20x lower sensitivity) but standard for agarose gels.

• Ethidium chloride: Incorrect. Not used for gel staining; chloride salts do not provide the specific fluorescence or binding affinity needed for nucleic acid detection.​

How It Works

Ethidium bromide inserts between DNA base pairs, enhancing fluorescence ~20-fold upon UV excitation. Gels are stained post-run (0.5 µg/mL solution, 15-60 min) or pre-cast with dye. Destaining reduces background. Note: It’s a mutagen—handle with gloves, dispose properly.

Safety and Alternatives

Safer options like SYBR dyes avoid EtBr risks while matching sensitivity, ideal for modern labs.

GATE Life Sciences Tips

This PYQ tests core molecular biology tools. Memorize: EtBr for agarose gels; UV transilluminator for viewing. Practice protocols: Pre-stain reduces waste; post-stain needs destaining for RNA.