Evidence of the Fluid Mosaic Model

Singer and Nicolson put forward the fluid mosaic model of membrane structure in 1972. The ‘fluid’ referred to the lateral movement of molecules in the membrane and the ‘mosaic’ to the random pattern of proteins.

The evidence for the mosaic came from freeze fracture electron microscopy. The cell membrane is fractured along the line of least resistance – the centre of the bilayer. The images produced have a speckled effect caused by the proteins exposed.

The evidence for fluidity comes from experiments. One such experiment is hybridisation of cells; this is where two cells are fused together.

An hour after fusion, the red and green dyed proteins have dispersed evenly across the membrane. This shows that the proteins move laterally within the membrane.

Different experiments involve dyeing either phospholipid or protein molecules, or attaching fluorescent markers and bleaching an area. Over time the bleached areas ‘disappear’, as the bleached and marked molecules mix.