The Process of Gel Electrophoresis
- Gel electrophoresis makes use of the principle that a substance (genetic material or proteins) will move or migrate through a medium having an electric current. Molecules will move through this medium at differing rates depending upon their molecular sizes and weights. The medium that is used in gel electrophoresis is called agarose gel, which is made from purified seaweed.
- Slots, called wells, are formed in the agarose gel and the lab workers will place a sample, such as a DNA sample, in these slots or wells. Lab workers also introduce a dye into the sample to make it more visible and easier to trace and record. Once an electric current is applied to the medium (the agarose gel) the molecules in the sample begin to move through the medium. Since the molecules do this at different rates, depending upon their size and weight, observing the streaks or marks left by the dye in the gel allows for analysis.
- The electric field in the gel medium has a positive pole and a negative pole. In the case of a DNA sample, the DNA contains a phosphate part to its structure and this part of the molecule carries a negative charge. Since opposites attract, this charge results in these molecules being attracted to, and moving toward, the positive pole in the electric field. Again, the smaller molecules move farther and faster in the medium than the larger ones, producing a separation. We can think of it almost as a race. The "winners," the "losers" and those in between spread out into an array that allows the researcher to make identifications.
- In other manipulations of the process, researchers may place special molecular markers in the medium. These are markers of known weight and characteristics that provide a means of indexing and identifying the sample molecules. Also, the chemical makeup of the medium may be adjusted according to the type of sample being tested. These alterations are done to optimize the conditions to a particular analysis.
