Gel electrophoresis separates macromolecules on the
basis of their rate of movement through a gel under the influence
of an electric field.
As the diagram indicates, mixtures of nucleic acids
are placed in wells near one end of a thin slab of a polymeric
gel. The gel is supported by glass plates and bathed in an aqueous
solution. Electrodes are attached to both ends, and voltage is
Since the nucleic acids are negatively charged, due
to the negatively charged phosphate group, they will migrate to
the positively charged electrode. However, their rate of movement
differs, as they have different sizes. The rate of movement is
inversely proportional to the size of molecules. That is, large
molecules move slower that small molecules.
This technique is used to identify and separate DNA
fragments that are cut by restriction enzymes.