ABSTRACT
Animal and plant tissues contain a mixture of cell types, and most cells contain multiple subcellular organelles. In order to study cells and organelles in isolation, it is desirable to have a homogeneous population of cells. Isolated cells can be grown in a plastic culture dish under appropriate conditions with defined growth medium. Cultures prepared directly from the tissues of an organism are referred to as primary cultures, while cells that have been made to proliferate to form large numbers and which can be repeatedly subcultured for weeks or months are referred to as secondary cultures. Subcellular fractionation is the breaking open of a cell and the separation of the various organelles from one another, usually by centrifugation. In order to study macromolecules and metabolic processes within cells, it is often helpful to isolate one type of subcellular organelle from the rest of the cell contents by subcellular fractionation.
