The term electrophoresis describes the migration of a charged particle under the influence of an electrical field. Many important biomolecules — such as peptide, proteins nucleotides and nucleic acids — possess ionisable groups and, therefore, at any given pH, exist in solution as electrically charged species either as cations (+) or anions (-).
Under the influence of an electric field these charged particles will migrate either to the cathode or to the anode, depending on the nature of their net charge.
The equipment required for electrophoresis consists basically of two items — a power pack, and an electrophoresis unit. Electrophoresis units are available for running either vertical or horizontal gel system. A typical vertical and horizontal gel electrophoretic apparatus are shown separately in Figs. 2.1 and 2.2.
The power pack supplies a direct current between the electrodes in the electrophoresis unit. All electrophoresis is carried out in an appropriate buffer, which is essential to maintain a constant state of ionization of the molecules being separated. Any variation in pH would alter the overall charge and, hence, the mobilities of the molecules being separated.
The introduction of the use of gels as support medium led to a rapid improvement in methods for analysing macromolecules. The earliest gel system to be used was the starch gel and, although this still has some use, the vast majority of electrophoretic techniques used nowadays involve either agarose gels or polyacrylamide gels.
Again, there are different types of Poly Acrylamide Gel Electrophoresis (PAGE) which are applied in separation of proteins and nucleic acids. Among these techniques Sodium Dodecyl Sulphate Poly Acrylamide Gel Electrophoresis (SDS- PAGE) was used widely. A typical SDS polyacrylamide gel separation of proteins is shown in Fig. 2.3. This technique is often used for purification of protein molecule.