Fluid-mosaic model 336 Subject

A detailed justification of the surfactant parameter approach is still the subject of theoretical investigations, and we will return to several issues below. We mention that the surfactant parameter approach is consistent with the fluid mosaic model of Singer and Nicolson. It tells us that the self-assembly of amphiphiles is driven by the strong segregation of water and hydrocarbon chains, and that packing effects dominate the self-assembly process. 

Most cell membranes contain about 60% lipid and 40% protein. Phosphoglycerides (such as lecithin and cephalin), sphingomyelin, and cholesterol are the predominant types of lipids found in most membranes. Precisely how the lipids and proteins are organized to form membranes has been the subject of a great deal of research. A widely accepted model called the fluid-mosaic model is diagrammed in I Figure 8.11. The lipids are organized... 

All P.p. are either hydrophobic, or they possess a strongly hydrophobic grouping, e.g. the phytol residue of chlorophyll. A simple model, in which P.p. are associated with the lipid layer of the thylakoid membrane, is however, unsatisfactory. It is necessary to propose a certain degree of ordered structure for P.p., and this is not possible if P.p. are subject to the random mobility of the lipid membrane components, as demanded by the fluid-mosaic model for membrane structure. Binding of a P. p. molecule to a protein would also be an unsatisfactory model, because the various P.p. would then be too widely separated for the efficient transfer of photons or resonance energy. A more feasible model would involve binding of several P. p. molecules to one protein, and there is much evidence for a system of this kind e.g. several chlorophyll-binding proteins have been isolated from... 

Until the 1990s, the most widely accepted model for the cell membrane was the fluid mosaic model. In this model, lipids and embedded membrane proteins were described as randomly distributed, with no particular in-plane distribution. This model is now considered simplistic, and current thinking is that biological membranes have a complicated in-plane organization. It is a controversial question whether the thermodynamic phase behavior of the constituent membrane lipids can play an important role in membrane function, and a large amount of literature on the subject has been written. 

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