Different gel systems have been developed to separate individual DNA, RNA or protein molecules in a mixture of molecules from each other. Samples are loaded in wells formed in the gel and then are pulled through the gel, usually by electric current. How gels resolve mixtures depends on a number of factors, but most commonly, gels resolve molecules on the basis of size. Each vertical row on a gel is referred to by scientists as a lane.
Electric current is applied, causing the protein samples to be drawn into the gel matrix.
As the samples are pulled toward the bottom of the gel, smaller proteins travel most quickly, larger proteins travel more slowly. After running the protein samples into the gel, the gel is stained to allow the proteins to be visualized. In this way, scientists can see how many different types of proteins are present, and what their relative sizes are. Since all the samples were initially loaded at the same horizontal level, the sizes of proteins in different lanes can be compared to each other, to see if neighboring lanes have similarly sized proteins. By running proteins of known size in adjoining lanes, the actual size of the proteins in the mixture can be estimated.