Electrophoresis
Electorphoresis is used to separate the components of mixtures of large molecules. During electrophoresis, an ion such as a nucleic acid or a charged protein molecule migrates in an electric field, through a molecular sieve (the gel). The rate of migration is determined by (1) the charge on the macromolecule, (2) the strength of the electrical field, (3) the size of the macromolecule, (4) the shape of the macromolecule, (5) the state of hydration of the macromolecule, (6) the viscosity of the solution, and (7) the pore size of the gel. During electrophoresis, large macromolecules migrate more slowly than small macromolecules. Macromolecules with low charge migrate more slowly than macromolecule with high charge. At its isoelectric point, an uncharged macromolecule (protein) does not migrate in an electric field. Electrophoresis can separate DNA fragments by size. DNA has a net negative charge and so migrates toward the positive pole in an electric field. Large DNA fragments migrate more slowly than small DNA fragments.