Electrophoresis is used to separate molecules of different sizes. Molecules with a negative charges such as proteins and DNA will migrate toward a positive charge.

A substance called agarose is often used to slow down the movement of molecules. Agarose acts as a sieve. Smaller molecules travel faster through the agarose than larger molecules.

Samples to be studied are placed in small wells in the agarose. Negative molecules will move to the positive side of the gel when electricity is applied. The smaller the molecule, the faster it can move through the gel.