Liquid mosaic model
The fluid mosaic model ( English fluid mosaic model is) one of Seymour Jonathan Singer and Garth Nicolson designed in 1972 model that the arrangement and organization of biological membranes describes.
description
According to the model, the double lipid layer is a two-dimensional solution of directed lipids and globular proteins . Lipids and integral membrane proteins can diffuse laterally unhindered in the lipid matrix (lateral diffusion ), provided this is not prevented by specific interactions. In addition to lateral diffusion, phospholipids can also perform transverse diffusion, the so-called flip - flop , which, however, proceeds much more slowly.
A third class of lipids, cholesterol , if involved in large amounts in the membrane structure, increases the viscosity of the membrane. The fluidity can also be regulated by varying the number of double bonds and the length of the fatty acid residues. Higher temperatures, short fatty acid residues and many unsaturated bonds also increase the degree of flowability.
At the same time as Singer and Nicolson, LD Frye and M. Edidin also carried out experiments on the structure of the cell membrane: They marked the membrane proteins of two cells with different dyes and then fused the cells. After about 40 minutes, the proteins on the new cell had mixed, so they must be mobile in the cell membrane.
The model is now largely considered to be out of date, since practically all basic assumptions are not given in reality: Membrane proteins are present in such high concentrations that they do not swim “far apart” in the lipid layer, but rather influence each other. In addition, most transmembrane proteins are much larger than the typical thickness of an undisturbed lipid bilayer. Biomembranes have a local order that is very difficult to observe directly. A few years ago, local functional order structures were discussed under the English term lipid rafts .
See also
literature
- Lubert Stryer: Biochemistry. 4th edition, Spectrum, 1999.
- Donald M. Engelman: Membranes are more mosaic than fluid . In: Nature . tape 438 , no. 7068 , December 2005, p. 578-580 , doi : 10.1038 / nature04394 .
Individual evidence
- ↑ SJ Singer, Garth L. Nicolson: The Fluid Mosaic Model of the Structure of Cell Membranes . In: Science . Vol. 175, No. 4023 , 1972, pp. 720-731 , doi : 10.1126 / science.175.4023.720 , PMID 4333397 , bibcode : 1972Sci ... 175..720S .