Posted by jayaram in Electrophoresis refers to the movement of charged molecules in an electric field. The negatively charged molecules move towards the positive electrode while the positively charged molecules migrate towards the negative electrodes.
Gel electrophoresis is a routinely used analytical technique for the separation/purification of specific DNA fragments. The gel is composed of either polyacrylamide or agarose. Polyacrylamide gel electrophoresis (PAGE) is used for the separation of smaller DNA fragments while agarose electrophoresis is convenient for the separation of DNA fragments ranging in size from 100 base pairs to 20 kb pairs. Gel electrophoresis can also be used for the separation of RNA molecules.
The DNA samples are placed in the wells of gel surface and the power supply is switched on. As the DNA is negatively charged, DNA fragments move through the gel towards the positive electrode. The rate of migration of DNA is dependent on the size and shape. In general, smaller linear fragments move faster than the larger ones. Hence, gel electrophoresis can be conveniently used for the separation of a mixture of DNA fragments, based on their size.
Agarose forms gels with pore sizes ranging from 100 to 300 nm in diameter. The actual pore size depends on the concentration of the agarose. The size of the pores determines the range of DNA fragments that can be separated on electrophoresis. For instance, a 0.3 agarose is used for the separation of DNA fragments between 5 and 50 kb, while a 5% agarose can separate 100-500 bp molecules.