Davson-Danielli model

In 1935, Hugh Davson and James Danielli proposed a model to explain the cell membrane consisting of a phospholipid bilayer between two layers of globular protein. Hydrophilic heads of phospholipids are towards proteins, forming a hydrophilic zone. Hydrophobic tails of phospholipids are between phosphate heads, forming a hydrophobic zone. There were problems with the model: not all cell membranes are identical and the placing of the proteins are different. If all cell membranes were identical, they would look alike under an electron microscope and would serve the exact same function (which all membranes do not). If proteins were layered on the surface of the membrane, their hydrophobic parts would be in an aqueous environment. Also it would separate the phospholipid heads (hydrophilic) from the water. Also membranes with different functions differ in chemical composition in structure, so this model cannot work for them all. In addition, the protein layer would make it unstable.