Gel electrophoresis Molecular Genetics Other Pages Gel Electrophoresis . Gels used in nucleic acid separation are matrices of agarose or polyacrylamide. These matrices have channels that are of molecular dimensions. Since nucleic acids are negatively charged, they migrate toward the positive pole in an electric field. When the electric field is applied through the gel, molecular sieving takes place.
Shorter chains move faster than longer ones.
Thus, the chains are spread out in the gel according to their size. Double-stranded DNA can be visualized by adding ethidium bromide, a flat aromatic chemical that fits between base pairs in the double helix. Autoradiography for radioactively labeled molecules.