See also: Membrane

In cellular Biology, the membrane indicates an assembly of molecules in a double layer separating the cell from its environment and delimiting the Organites inside this one. The membrane is a complex whole of Lipide S, Protéine S and Sucre S controlling the exchanges of matter between the interior and the outside of the cell or between two cellular compartments by conveying , budding of blisters, Phagocytose, etc . The component-key of the biological membrane are the Phospholipides. They have the capacity car-to be organized in a double layer, their absorbent heads pointing towards hydrophobic outside and their chains pointing towards the interior.

One speaks about plasmic Membrane, or plasmalemme, when this one delimits a cell (the interior medium is then the Cytoplasme). One speaks about intracellular membrane, or endomembrane, when it delimits a Organite (p.ex. membrane mitochondriale, nuclear, lysosomiale, etc ).

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History

• 1655 : Robert Hooke observes for the first time of the cells using a Microscope with two lenses. It uses this name in its original direction which indicates a small room.
• 1632 - 1723: Antoni van Leeuwenhoek observes for the first time of the Protozoaires, the Bactérie S and the red globules thanks to its Microscope.
• 1813 : Eugene Chevreul describes the concept of Fatty-acid. It publishes in 1823 its “Research chemical on the greasy substances of animal origin”.
• 1847 : Nicolas Theodore Gobley isolates the Lécithine from the egg yolk. It is in fact the discoverer of the Phospholipide S.
• 1855: Von Nägeli and Carl Eduard Cramer creates the concept of membrane as a barrier to explain the osmotic phenomena.
• 1890 : Lord Raleigh carries out a series of experiments on the interface water-oil and calculates the thickness of an oil film on the surface of a stretch of water.
• 1895-1899: Charles Ernest Overto discovers that the capacity of a substance to cross the membrane depends on its character Hydrophobe. He formulates the assumption of a membrane made up of lipids.
• 1917 : Irving Langmuir studies the structure of films of oil at water surface. He formulates the assumption of full-course of Fatty-acid being directed vertically, the carboxyl group directed towards water and the chain alkyl directed towards the air.
• 1925 : Gorter and Grendel show the capacity of certain lipids to form the simple ones and double-layers. They also show that the surface of the lipids extracted the red globules is equal to twice the surface of these cells. They are thus the first to formulate the assumption of a formed cellular membrane of a double-layer of lipids.
• 1935 : James Frederic Danielli and Hugh Davson formulate the assumption of a cellular membrane made up of double-layered of lipids in sandwich between two layers of Protéine S.
• 1965 Bangham, Standish and Watkins synthesizes the first Liposome S starting from egg Lécithine dehydrated.
• 1972 : Jonathan S. Singer and Garth L. Nicholson reconsider the assumption of Danielli and Davson and describe the model of the mosaic fluid . The membrane is always organized into double-layered but the polar heads of phospholipides are directly in contact with water. The membrane proteins “float” in or in surface of the lipids.
• 1985 : Publication of the first structure of protein membrane with high-resolution.
• 1997 : Kai Simons and Elina Ikonen formulate the assumption of the lipidic rafts. The Sphingolipide S and the Cholestérol would have the capacity to gather to form a platform of attachment to certain membrane proteins.

Double-layered lipidic

A membrane is made up of a double-layered of Lipide S , are lipids amphipathic (Phospholipide S in the majority of the cases), each lipid having its polar head Hydrophile (negatively charged phosphates) directed towards the outside of the membrane and its tail Hydrophobe (chain of saturated fatty-acid and unsaturated fatty-acid) directed towards the interior. Its thickness is of approximately 7,5  Nm. The cytoplasmic membrane is described as " dynamique" from its constant renewal.

The model of the fluid mosaic

The term of mosaic fluid , due to Singer and Nicholson

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