Centrifugation can be used to break up cells into fragments and is the first step in most fractionations. The suspension of cells produced from this process is called a homogenate or extract. There are different speeds for centrifuging ranging from low speeds to extremely high ones. After centrifugation, the cell homogenate separates into the pellet and supernatant. The pellet is usually components of the cell that collects at the bottom of the centrifugation tube and the supernatant refers to the layer above the pellet. It is possible to subject the supernatant to multiple rounds of centrifugation for further purification.
A preparative ultracentrifuge separates cell components by size and density by generating enormous centrifugal forces. It does this by rotating extracts of broken cells at high speeds. 
- ↑ Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. (2008: 510-511) Molecular Biology of the Cell, 5th edition, Abingdon: Garland Science