Davson-Danielli model.

The advent of electron microscope technology added more data that seemed to confirm the bilayer hypotheses. However the lack of uniformity of the layers raised questions about the relative positions of the proteins known to be an important parts of the membrane

A lipid bilayer where two layers of polar lipid molecules are arranged with their

hydrophilic heads outward.

A layer of protein covering the surfaces of the membrane. Note that the protein

layer is embedded in the layer of lipids, holding them in place.

In this model, the lipids are not free to move around.

Freeze fracture techniques