Question

Explain how gel electrophoresis of DNA samples works and why it was performed.

Answer 1

Gel electrophoresis is a technique where in DNA from a sample is run on a acrylamide gel under an applied voltage. DNA is a polymer of dNTP and carries a negative charge due to the phosphate present in the backbone. A pure sample of DNA extracted from a source is loaded in wells in the agarose gel. The DNA is run on the gel in a running buffer in the chamber under a voltage that is applied through the running buffer. DNA being negative in charge moves towards the positive electrode on the gel. Since DNA irrespective of source, composition and other factors will always carry a negative charge, the DNA molecules are separated on the gel on the basis of their length. The smaller the DNA molecule, faster will the molecules move on the gel and will be separated before others. This technique in its basic form is performed to check if the DNA has not degraded. Intact dna will give a very thick and constrict band, however, if the DNA has degraded or is impure it will give a streak and not a clear band. It I also employed in other techniques like electrophoric mobility assay where in a protein usually interacts with DNA, such complex is run on the gel along with DNA alone in another well, if the DNA complexes with the protein moves slower than there can be concluded a binding between the DNA and protein.