Overview of cell fractionation

This discussion unit describes the most common methods for cell fractionation which provides the essential ingredients for the increasing number of cell-free assays now being used in test-tube reconstructions of complex cellular events involving intercompartmental interactions. Gel filtration separates on the basis of size, centrifugation separates on the basis of size and density, and electrophoresis separates on the basis of surface charge density. Centrifugation is the most widely used procedure in cell fractionation and is the only approach commonly used to separate crude tissue homogenates (often having quite large volumes) into subfractions as starting material for more refined purification procedures. Therefore, this overview focuses primarily on fractionation of organelles by centrifugation.