Biotechnology: Principles and Processes — BIOLOGY STD 12 Science — Question

→ The techniques used for separation and isolation of DNA fragments is known as gel electrophoresis.
→ In this method Agarose gel is used as a medium.
→ The cutting of DNA by restriction endonucleases results in the fragments of DNA.
→ These fragments can be separated by a technique as shown in figure.

→ Since, DNA fragments are negatively charged molecules they can be separated by forcing them to move towards the anode under an electric field througha medium/matrix.
→ The DNA fragments separate (resolve) according to their size through sieving effect provided by the agarose gel.
→ Hence, the smaller the fragment size, the farther it moves.
→ The separated DNA fragments can be visualised only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation.
→ DNA appears as bright orange coloured bands of DNA in an ethidium bromide stained gel exposed to UV light.
→ The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. This step is known as elution.
→ The DNA fragments purified in this way are used in constructing recombinant DNA by joining them with cloning vectors.