Arrange the steps of agarose gel electrophoresis in a correct sequence :

(A) Visualisation of DNA fragments under UV light
(B) Movement of the DNA fragments under electric field towards anode
(C) Loading the DNA in the wells
(D) Staining of DNA fragments with ethidium bromide

Choose the correct answer from the options given below:

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

The correct answer is Option (3) → (C), (B), (D), (A)

(C) Loading the DNA in the wells

(B) Movement of the DNA fragments under electric field towards anode

(D) Staining of DNA fragments with ethidium bromide

(A) Visualisation of DNA fragments under UV light

The process of cutting DNA using restriction endonucleases results in the formation of DNA fragments. These fragments can be separated using a technique called gel electrophoresis.

The DNA samples are first loaded into wells within the agarose gel.Since DNA fragments are negatively charged molecules, they can be separated by applying an electric field, causing them to move towards the anode through a medium or matrix. Agarose, a natural polymer extracted from seaweeds, is commonly used as the matrix. The DNA fragments separate based on their size due to the sieving effect provided by the agarose gel. Smaller fragments move farther compared to larger fragments.

The separated DNA fragments can be visualized only after staining the DNA with a compound called ethidium bromide, followed by exposure to UV radiation. Without staining, the pure DNA fragments cannot be seen in visible light. After staining, you can observe bright orange-colored bands of DNA in an ethidium bromide stained gel exposed to UV light. Once the DNA fragments are separated, they can be cut out from the agarose gel and extracted from the gel piece. This step is known as elution. The purified DNA fragments obtained through elution are then used in constructing recombinant DNA by joining them with cloning vectors.