Electrophoresis

Electrophoresis may be described as the migration of electrically charged particles through a substance, serving as a carrier, in an electric field. In electrophoresis, the speed of migration is proportional to the field strength and to the ion charge, however, it is inverse proportional to the particle radius and the viscosity of the substance. With one kind of electrophoresis - gel electrophoresis -, the ratio between the particle radius and the pore diameter of the carrier may also be important. Here, the particle radius influences more profoundly the speed by which the particles pass through the gel,the gel is thus acting as a molecular sieve. Electrophoresis is used for the separation of substance mixtures, particularly for molecule mixtures. Liquids, gels (gel electrophoresis) or solids are applied as carriers for electrophoresis.

Standard electrophoresis procedure

A standard procedure of electrophoresis is the SDS page procedure (sodium dodecyl sulfate polyacrylamide gel electrophoresis). With this kind of electrophoresis, adding SDS levels differences in the electric charges of the proteins, denaturing the tertiary structure. The separation thus proceeds only according to the molecular mass. SDS is a negatively charged detergent whose aliphatic side attaches to the protein molecules. The negative side of the detergent repels the negative SDS molecules which are bound in the vicinity. This generates a complete linearity of the protein molecules, though only if the protein does not have any disulfide linkage. It is obvious that the larger the protein molecule, the longer is the originating SDS-charged chain. The charge of the proteins therefore can be neglected.

Mobility of electrophoresis

The requirement for carrying out a separation by electrophoresis is the different electrophoretic mobility of two particles to be separated. Electrophoretic mobility consists of many physical factors which influence the migration velocity of a particle during electrophoresis. Movement of the particles is caused by a propelling force which affects a particle of a specific charge in an electrical field of defined strength. Against this force acts another force, which arises from viscosity and size of the particle. This force can be deduced from Stokes law. Nevertheless, this assumption is valid only in the ideal state. In reality, other factors play a role, such as the hydration shell, the ion cloud, the dissociation level of the electrolyte and effects which are caused by the carrier.

Application of electrophoresis

Electrophoresis is applied above all as an analysis procedure in biology and medicine, the main application being DNA analysis. This kind of electrophoresis exploits the possibility to separate molecules of different length. Besides, electrophoresis can be used for the separation of proteins and in proteome research.

Literature

• http://de.wikipedia.org/w/index.php?title=Elektrophorese&oldid=86841624 (called: 31.03.11).
• http://www.uni-leipzig.de/~bioanaly/sem6/Biochem.Meth.Teil.3.Elektrophorese.040608.pdf (called: 31.03.11).