Membranes in Motion The Fluid Mosaic Membrane Model


It isn’t every newsletter issue that FOCUS has the privilege of featuring a scientist whose theory of a fundamental biological phenomenon is accepted throughout the biological and medical sciences as the standard textbook model.


Such is the case with S. J. Singer’s and Garth Nicolson’s landmark theory of the Fluid Mosaic Model of cell membranes. This model, proposed


The cell membrane is, in the deepest sense, where it’s at— it’s the place where a cell de- fines itself to other cells and the extracellular environment— where the outside world is sep- arated from an inside world. It is also a dynamic, ever shifting struc- ture where informa- tion is exchanged and biological reac- tions begin and end. The chemistry of life, the exchange and synthesis of molecules, and the transfer of electrons, all occur along and across biological membranes. The cell membrane contains channels and pumps that con- trol the flow of substances and information between cells, and it contains highly specific re- ceptors that allow cells to re- spond to their external milieu and identify and communicate with other cells. It is also the place where nerve impulses are


in 1972 and published in the prestigious journal SCIENCE, has been called a “unified theory” of the cell membrane. This model has been tested and retested for many decades, and it is now believed to accurately predict the structure and behavior of all cellular membranes. Over the intervening years this theory has been confirmed by many sophisticated physical and chemical techniques, including one known as freeze-fracture electron microscopy.


transmitted along nerve cells by changing the electrical po- tential across the membrane.


When intact and functional, fluid membranes are at the center of good health; oxidized,


vehicles, and enzyme and com- munication sites.


It wasn’t until 1972, with Singer’s and Nicolson’s theory, that we were able to explain all of the properties of cellular membranes and where each component fit into the structure.


damaged membranes leads to pathology and illness. And this is true of both the cell and its outer membrane barrier or cell membrane, and the membrane structures inside the cell, such as in the mitochondria, the little energy powerhouses in- side each cell, which are little semi-autonomous organelles on their own. They, too, have membranes that are important as electrical barriers, transport


The cell membrane was first proposed—as a double layer or bilayer of lipids—in 1925, almost ninety years ago, and it was a revolutionary proposal at the time, but it took several years later to deter- mine where proteins and other components actually fit into this structure. It wasn’t un-


til 1972, with Singer’s and Ni- colson’s theory, that the theory came into its own, fully eluci- dated and able to explain all of the properties of cellular mem- branes and where each compo- nent fit into the structure.


They proposed that:


Membrane components (lipids, glycolipids, proteins, glyco- proteins, etc.) are amphipathic in structure—that is, they are


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