The movement of charged molecules or ions under the influence of an electrical field is called Electrophoresis. Biological molecules such as Amino acids, proteins, peptides and nucleic acids can be separated using this technique. Depending on the net charge, the sample migrates towards the cathode or anode. If the sample contains positively charged molecules it moves towards the Cathode (Negative Electrode) and if the sample contains negatively charged molecules it migrates towards the Anode (Positive Electrode).
Gel electrophoresis is a commonly used analytical technique for the separation and purification of DNA fragments. DNA fragments being considerably larger molecules as compared to proteins they are separated on Agarose gels. The DNA samples are placed inside the wells in the gel surface and the power supply is switched on. DNA being negatively charged molecules, migrates towards the Anode. The rate of migration depends on the size and shape of the DNA fragments.