One of the most fundamental aspects of cell biology is the detection, urification and analysis of the roughly 10,000 unique proteins in a cell. To achieve this feat, various genetic techniques and experimental procedures that exploit the expression of genes (like metabolic labeling) have recently been developed. There are, however, older non-genetic techniques which are even more commonly used. These techniques are generally based on a physical or functional property of the protein. A group of hymogenized cells that have been grown up in a cell culture can be used as a source of the protein of interest.

Separation of these proteins is usually based on size and/or mass (like gel filtration chromatography, differential velocity sedimentation centrifugation, equilibrium density sedimentation, and SDS-PAGE), but is sometimes based on other things like their net electric charge (this is often a factor in various types of electrophoresis, but is especially apparent in ion-affinity chromatography) or enzymatic or immuno-properties (like antibody affinity chromatography and western blotting). Membrane proteins can be particularly hard to isolate, because they tend to not want to leave the membrane (for more information on this see membrane protein).

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