Electrophoresis

The electrophoresis is - with the Chromatographie - the principal one of the techniques used in biology for the separation and the characterization of the molecules. It has some applications in chemistry, but is mainly used in Biochimie or Molecular biology for the separation of the Protéines or that of the nucleic acid . In a given medium, the separation of the particles is done according to their load Q and for Q identical, according to their size.

Description

The Technique of the electrophoresis is based on the displacement of Ion S (Molécule S having lost their electric neutrality) under the effect of a Electric field. Because of their particular characteristics and according to the conditions of the electrophoresis these ions will have different speeds of migration, they thus will separate from/to each other.

The ic molecules Anion (-) migrate towards the Anode (+) and the molecules ic Cation (+) move towards the Cathode (−).

There exists on the level of the macromolecules two types of proteins charged:

Electrophoresis in liquid vein

The electric field east provides by a generator of D.C. current. The support of this field is consisted a Tampon of suitable pH and concentration whose Ion S lead the current of a pole to another. This support can be liquid: one speaks then about electrophoresis in liquid vein (developed by Tiselius in 1937).

Electrophoresis of zones

The principal applications use a support porous stabilizing the liquid Phase: one speaks then about electrophoresis on support or electrophoresis of zones. The mixture to be separated is deposited on a support suitable, porous and impregnated plug (paper, derived from cellulose, polyoside “agarose”, polyacrylamide…). The support must be homogeneous, porous and inert. In fact, the condition of inertia is never observed and the support plays a more or less important part in separation.

The various types of electrophoreses of zones are often named according to the form of mediums:

There exist many types of electrophoreses, of which:

  • isoelectric focusing (electrophoresis in a gradient of pH);
  • electrophoresis on polyacrylamide gel (or PAGE for in '' Poly-Acrylamide Freezing Electrophoresis '');
  • electrophoresis in gel of agarose;
  • two-dimensional electrophoresis;
  • electrophoresis in pulsated field;
  • electrophoresis in denaturing conditions (in the presence of detergents of the type SDS, or in the presence of Urea or other agents Chaotropique S).

Freezing of electrophoresis

  • the polyacrylamide gels can be of two types: SDS-PAGE or Sorting-Tricine. Gel SDS PAGE is used to make migrate of proteins, the gel Tris Tricine make it possible to visualize proteins of small size of which the number of amino-acid is lower than 150: peptides.
  • the gel of agarose as for them is used to make migrate of the nucleic acids.

See too

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