Question

Which dye is most commonly used for DNA visualization in agarose gel?

• A. Ethidium bromide
• B. Crystal violet
• C. Coomassie blue
• D. Safranin

Hint:

Always associate Ethidium Bromide (EtBr) with DNA/RNA agarose gels and UV light visualization. Also, remember that it requires careful handling because its intercalating nature makes it a potential mutagen.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
After DNA fragments are separated by size using agarose gel electrophoresis, the DNA must be stained to be visible.
Since DNA is naturally colorless, specific fluorescent dyes are used to label the molecules for visualization under special lighting.

Step 2: Detailed Explanation:
Let's review the applications of the given dyes.
- Ethidium bromide (EtBr): This is the classic and most commonly used fluorescent dye for visualizing nucleic acids in agarose gels.
It acts as an intercalating agent, meaning its flat molecular structure allows it to slip directly between the stacked base pairs of the DNA double helix.
When exposed to ultraviolet (UV) light, the intercalated EtBr fluoresces with a bright orange-red color, clearly revealing the location of the DNA bands.
- Crystal violet \& Safranin: These are chemical dyes primarily used in microbiology for the Gram stain technique to differentiate bacterial cell walls, not for routine DNA gel staining.
- Coomassie blue: This is a highly common stain used exclusively for visualizing proteins in SDS-PAGE gels, not for DNA.

Step 3: Final Answer:
Ethidium bromide is the correct dye for DNA visualization in this context.
Therefore, option (A) is the correct answer.