Electrophoresis is an analytical method in which a controlled electric current is used in order to separate biomolecules according to their size to electric charge ratio, using a gelatinous matrix as a base.
Electrophoresis is used in a great majority in the field of recombinant DNA since it allows us to know the charge that polypeptides have, and to separate the different polypeptides resulting from the variations of the recombinant DNA experiment.
The most commonly used variant for the analysis of mixtures of proteins or nucleic acids uses a gel as a support, usually made of agarose or polyacrylamide. Nucleic acids already have a negative electrical charge, which will direct them to the positive pole, while proteins become charged by binding with substances such as SDS that incorporate negative charges in a way that is dependent on the molecular mass of the protein.
By putting the mixture of molecules and applying an electric field, they will move and must go through the gel mesh (a three-dimensional network of crossed fibers), so that the small ones will move better, faster. Thus, the smallest will advance further and the largest will be close to the starting point.