Differential centrifugation

Differential centrifugation is a common procedure in microbiology and
cytology used to separate certain organelles from whole cells for
further analysis of specific parts of cells. In the process, a tissue
sample is first homogenised to break the cell membranes and mix up the
cell contents. The homogenate is then subjected to repeated
centrifugations, each time removing the pellet and increasing the
centrifugal force. Finally, purification may be done through
equilibrium sedimentation, and the desired layer is extracted for
further analysis.
Separation is based on size and density, with larger and denser
particles pelleting at lower centrifugal forces. As an example,
unbroken whole cells will pellet at low speeds and short intervals
such as 1,000g for 5 minutes. Smaller cell fragments and organelles
remain in the supernatant and require more force and greater times to
pellet. In general, one can enrich for the following cell components,
in the separating order in actual application:
Whole cells and nuclei;
Mitochondria, lysosomes and peroxisomes;
Microsomes (vesicles of disrupted endoplasmic reticulum); and
Ribosomes and cytosol.