| |
The Fluid Mosaic Model
The fluid mosaic model was first proposed by S. J. Singer and G. L. Nicolson in 1972 to describe the structure of cell membranes (Singer and Nicolson 1972). In this now-accepted model, phospholipid molecules, each with one hydrophobic, and one hydrophilic end, make up most of the membrane. The hydrophilic heads form the inner and outer surfaces the membrane and the hydrophobic tails, which are repelled by the water within and outside the cell, are sandwiched in between (see figure). This is known as the lipid bilayer.
This arrangement is fluid, not solid, because the various functional macromolecules embedded in the phospholipid matrix can move about the surface of the cell. Because of this fluidity such membranes are often called plasma membranes (one meaning of plasma is a complex fluid).
The model is called mosaic because it proposes that the membrane is made up of many different parts, including proteins, carbohydrates, and lipids (see figure). This composite structure allows the membrane to perform multiple functions.
|
