The endocytose (Greek endon (inside) and kutos (cell)) is the mechanism of transport of molecules even of particles (viral, bacterial, etc) towards the interior of the cell.

The endocytose (or internalisation) takes place when part of the membrane (or plasmic phase shift of the fluid for the cells deprived of solid membrane surfaces it) completely surrounds a particle or a large molecule and makes it penetrate outside towards the interior of a cell. This event membrane (or quasi-membrane) is very important in the life of a cell, because it makes it possible to control the presence with the protein membrane like the receivers, and to answer stimuli coming from outside.

The endocytose of a molecule is held in several étapes : there is initially specific addressing of the molecule in the wells of endocytose, which are zones of the membrane specialized in the endocytose, then fixing on the inner face of the membrane of cadhérines, then, under the action of the clathrines, invagination of the membrane, and vesicularisation and finally, the detachment and the migration of the blister towards the interior of the cell. Then, the clathrines are detached from the wall of the blister which becomes a smooth blister.

According to the size of the absorptive material, one distinguishes two processus :

• pinocytosis (" boisson" cell),

which is the ingestion of fluids or macromolecules by means of small blisters of diameter lower or equal to 150 Nm;

• phagocytosis (" alimentation" cell),

which is the absorption of large particles, even of cells, by blisters of diameter always higher than 250 Nm and being able to reach several micromètres : phagosomes.

There exists also a type of endocytose said by receiver: the particles present on their membrane of specific proteins recognized by the corresponding membrane receivers. In the lysosome, the protein is lysed; the receivers are recycled and returned on the membrane (ex: the cholesterol, which uses as specific protein Apo B and membrane conveyer the LDL).

Examples

1. the Cholesterol, present in two forms in the vessels sanguins : LDL (Low Density Liposoid) and HDL (High Density Liposoid). Cholesterol necessary to the extracellular matrix is taken in the extracellular medium by pinocytosis of the LDL.
2. the phagocytose : mechanism allowing to introduce a foreign body in order to digest it (animal unicellular) or to destroy it (macrophages of the Immune system). It is a normal endocytose, then lysosomes position around the blister and pour their enzymes which will hydrolize the body thus introduced.

See too

Exocytose

External bonds

• http://virologie.free.fr/documents/virologie/03-transport_intracell_prot/transport_intracell_prot.htm

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