Question

DNA staining by ethidium bromide is followed by the exposure to UV rays. Now DNA is seen as bands of

• A. Blue colour
• B. Orange colour
• C. Both B and C
• D. Red colour

Answer 1

The correct option is B Orange colour

Agarose gel electrophoresis
Agarose gel electrophoresis is the technique involving the separation of molecules based on their size and charge.

Process of Agarose gel electrophoresis
Process of Agarose gel electrophoresis is as follows

• The DNA fragments and size markers are loaded onto the gel well and current is passed through the gel. ​​​​​​​
• The DNA being negatively charged, moves towards the positive electrode during gel electrophoresis.
• The smaller the size of the molecule, the faster and farther it travels and the fragments are separated

Visualisation of DNA in the agarose gel.
Visualisation of DNA in the agarose gel is done in the following way:

• To visualise DNA in the agarose gel, a positively charged dye ethidium bromide (EtBr) is added in the agarose gel or electrophoresis buffer.
• This dye intercalates itself into the DNA backbone and gives orange fluorescence upon exposure to the UV light.
• Thus, DNA is visualised by exposure to UV light as orange coloured bands on the agarose gel.

Final answer
​​​​​​​(b) Orange colour