What is the fluid mosaic model?

The Fluid Mosaic model, first proposed by S.J. Singer and Garth L. Nicolson in 1972, describes the structure of the plasma membrane.

According to the Fluid Mosaic model the plasma membrane consists of a lipid bilayer that is made up of a mosaic of components, primarily phospholipids, proteins, cholesterol and carbohydrates. The components move freely and fluidly in the plane of the membrane. This constant movement gives the cell membrane its flexible, fluid character. It also helps the cell membrane maintain its role as a barrier between the internal and the external cell environments.

Plasma membranes range from 5 nm to 10 nm in thickness. The proportions of lipids, proteins, and carbohydrates in the plasma membrane vary among cell types.

The Fluid Mosaic model is the preferred model for scientists today and replaces the older Membrane Unit model, which stated that the cell membrane is made up of three layers with two protein layers flanking a central phospholipid layer.