Conducting a fair race

Electrophoresis uses electricity as the force to move the DNA molecules through the gel. The electrophoresis apparatus is designed to run a fair race by conducting the current evenly across the gel (Fig. 14). A wire is found along the bottom of the apparatus at both ends. Electrons supplied by the electrophoresis buffer will flow to the positive pole. The phosphates making up the DNA molecule's backbone create a negative charge so DNA will move toward the positive pole once the circuit is complete. As long as the current is flowing, DNA molecules will be subjected to the same force (the voltage) which carries them toward the positive end of the gel. This will cause the DNA fragments to move in a straight lane rather than wander toward the positive end. Therefore, each well in the electrophoresis gel establishes a lane for the DNA sample.

Fig. 14. Current is run through the gel by connecting it to a power supply. (Image by D. Lee)