Question

Which of the following steps should be performed in order to visualize the bands of DNA fragments by gel electrophoresis?

• A. Exposure of DNA fragments to UV radiations
• B. Staining with bromophenol blue followed by exposure to UV radiations
• C. Staining with ethidium bromide followed by exposure to UV radiations
• D. Staining with ethidium bromide

Answer 1

The correct option is C Staining with ethidium bromide followed by exposure to UV radiations

Due to the action of restriction enzymes on the DNA molecule, fragments of DNA are formed.

Gel electrophoresis is carried out for separating these fragments of DNA. During the preparation of sample for gel electrophoresis, ethidium bromide and bromophenol blue are added.

DNA cannot fluoresce on its own. Ethidium bromide intercalates with the DNA. Ethidium bromide stains the DNA as bright orange bands when it is illuminated with UV rays. This is utilised for visualization of DNA molecules.

Bromophenol blue is known as the tracking dye as it runs fastest in the sample and tracks the migration of the sample during the run-time.