In cell biology or molecular biology research, homogenization is a process whereby a biological sample is brought to a state such that all fractions of the sample are equal in composition, i.e. a homogenized sample is mixed so well that removing some of the sample does not alter the overall molecular make-up of the sample remaining, and is identical to the fraction removed. Homogenization in biology is often followed by, or combined with, cell lysis and/or molecular extraction.
Homogenization of tissues in solution is often performed simultaneously with cell lysis. To prevent lysis however, the tissue (or collection of cells, eg. from cell culture) can be kept at temperatures slightly above zero to prevent autolysis, and in an isotonic solution to prevent osmotic damage.
If freezing the tissue is possible, cryohomogenization can be perform under "dry" conditions, and is often the method of choice whenever it is desirable to collect several distinct molecular classes (eg. both protein and RNA) from a single sample, or combined set of samples, or when long-term storage of part of the sample is desired. Cryohomogenization can be carried out using a supercooled mortar and pestle (classic approach), or the tissue can be homogenized by crushing it into a fine powder inside a clean plastic bag resting against a supercooled solid metal block (more recently developed and more efficient technique).
High-pressure homogenization is used to isolate the contents of Gram-positive bacteria, since these cells are exceptionally resistant to lysis, and may be combined with high-temperature sterilization.
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