Arrange the following steps of gel electrophoresis in correct sequence :

(A) Staining the DNA with ethidium bromide

(B) Movement of DNA fragments towards anode under an electric field through agarose

(C) Exposure to UV radiation

(D) Separation of DNA fragments according to their size

Choose the correct answer from the options given below:

(B), (D), (A), (C)

The correct answer is Option (1) - (B), (D), (A), (C)

(B) Movement of DNA fragments towards anode under an electric field through agarose

(D) Separation of DNA fragments according to their size

(A) Staining the DNA with ethidium bromide

(C) Exposure to UV radiation

During gel electrophoresis, DNA fragments separate based on their size and charge. The gel, typically made of agarose, acts as a molecular sieve that slows down the movement of DNA fragments as they migrate through the gel under the influence of an electric field.

When an electric field is applied, the negatively charged DNA fragments move towards the positively charged anode. Smaller DNA fragments can move through the gel more easily and thus migrate faster towards the anode compared to larger fragments. As a result, DNA fragments separate into distinct bands according to their size, with smaller fragments traveling farther from the origin (where the DNA was initially loaded onto the gel) and larger fragments staying closer to the origin.

Ethidium bromide is a fluorescent dye commonly used to stain DNA in agarose gels. When ethidium bromide intercalates between the base pairs of the DNA, it becomes fluorescent. After gel electrophoresis, the gel is exposed to UV light, and the ethidium bromide-stained DNA bands emit a bright orange fluorescence, allowing researchers to visualize and analyze the separated DNA fragments. Without staining with ethidium bromide and exposure to UV light, DNA fragments are not visible in visible light, making it impossible to observe and analyze the results of gel electrophoresis.