ABSTRACT
Electrophoresis When placed in an electric field, molecules with a net charge, such as proteins, will move towards one electrode or the other, a phenomenon known as electrophoresis. The greater the net charge the faster the molecule will move. In polyacrylamide gel electrophoresis (PAGE), the electrophoretic separation is carried out in a gel, which serves as a molecular sieve. Small molecules move readily through the pores in the gel, whereas larger molecules are retarded. The gels are commonly made of polyacrylamide, which is chemically inert and which is readily formed by the polymerization of acrylamide. The pore sizes in the gel can be controlled by choosing appropriate concentrations of acrylamide and the cross-linking reagent, methylene bisacrylamide. The higher the concentration of acrylamide used, the smaller the pore size in the final gel. The gel is usually cast between two glass plates separated by a distance of 0.5-1.0 mm (Figure 1). The protein sample is added to wells in the top of the gel, which are formed by placing a plastic comb in the gel solution before it sets (Figure 1). A blue dye (bromophenol blue) is mixed with the protein sample to aid its loading on to the gel. Because bromophenol blue is a small molecule, it also migrates quickly through the gel during electrophoresis and so indicates the progress of electrophoresis.
