Sandwich (Davson–Danielli) model of cell membrane


The cell membrane is a thin layer that separates the interior of a cell from its surroundings. It regulates the movement of substances in and out of the cell and maintains its shape and integrity. The cell membrane is also involved in various cellular processes such as signaling, adhesion, and recognition.

But what is the structure of the cell membrane? How is it composed of different molecules and how are they arranged? These questions have intrigued scientists for a long time and have led to the development of various models to explain the cell membrane structure.

One of the earliest and most influential models was proposed by Hugh Davson and James Danielli in 1935. They based their model on the observation that the cell membrane was electrically polarized, meaning that it had different charges on its two sides. They also considered the chemical composition of the cell membrane, which was known to contain lipids and proteins.

The Davson–Danielli model suggested that the cell membrane consisted of a lipid bilayer sandwiched between two layers of proteins. The lipid bilayer was composed of phospholipids, which are molecules that have a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail. The hydrophobic tails faced each other in the middle of the bilayer, while the hydrophilic heads faced the aqueous environment on both sides. The protein layers were made of globular proteins that coated the lipid bilayer and provided stability and functionality to the membrane.

The Davson–Danielli model explained some of the properties and functions of the cell membrane, such as its selective permeability, electrical polarization, and thickness. It also received support from electron microscopy images that showed the cell membrane as two dark lines with a lighter region in between. However, it also faced some problems and limitations that eventually led to its rejection and replacement by a more accurate model.

In this article, we will explore the key features, support, problems, and falsification evidence of the Davson–Danielli model. We will also introduce the fluid-mosaic model that replaced it as the current accepted model of cell membrane structure.