Fluid-mosaic model

The fluid-mosaic model, as proposed by Singer and Nicolson, is used to describe how the components of the plasma membrane are thought to interact. The lipid bilayer is proposed to be a dynamic fluid in which:

• the polar heads of a membrane phospholipids exchange places with each other rapidly on one side of the membrane, but rarely exhibit jumping to the other side of the membrane across a hydrophobic core; this has been shown by electron spin resonance studies
• some transmembrane proteins are highly mobile within the plasma membrane; demonstrated by fusing human and mouse cells after labelling of their cell surface proteins with red and green fluorescent antibody complexes respectively. Complete mixing of the colours in the hybrid cell occurred within an hour.

Other membrane proteins are less mobile due to local interactions e.g. cytoskeletal and extracellular filament connections on both sides of the cell. Hence, the model is described as being a modified fluid-mosaic.