Protein Function in Cell Membranes

“Function of proteins in the cell membrane”

Since 1972 the ‘Fluid Mosaic Model’ has been used to describe the structure of the cell membrane. This model consists of a phospholipids bi-layer and a variety of proteins spread throughout the membrane surface. Proteins themselves play an important role in the membrane to ensure the cell can live as efficiently and effectively as possible.

Firstly, structural proteins are found attached to microfilaments in the cytoskeleton which ensures stability of the cell. Secondly, cell recognition proteins allow cells to recognise each other as from the same organism. These proteins are found dispersed as markers throughout the membrane. The lack of these proteins would see the body attack other cells in the same organism as it would recognise the cell as ‘foreign’. This is the concept behind rejection after tissue transplantation. This concept ensures the immune system can work efficiently by knowing what cells are ‘foreign’ to the organism. Thirdly, enzyme proteins are crucial in producing a variety of substances essential for cell function. These enzymes are found throughout the cell membrane and allow the cell to synthesise and break down substances according the cell’s requirements.

Another example of proteins in the cell membrane is receptor proteins. These proteins are the connection between the cells internal and external environments. This connection is important as it enables the cell to adapt depending on changes to the cells external environment. Receptor cells extend right across the cell membrane and have active sites specific to an antigen or substrate. The enzyme changes shape, once the substrate binds to the enzyme. This change in shape leads to a metabolic pathway being formed in the cell which changes gene expression. The changes in gene expression can lead to substances (example- hormones) being produced or changes in cellular activity that is required for the cells survival. Finally, transport proteins play an important role in the maintenance of concentrations of ions and such like. These transport proteins come in two forms: carrier proteins and channel proteins. Channel proteins are involved in using the energy released from ATP being broken down to facilitate active transport and ion exchange. This is of course an important process as ions cannot always enter the cell by diffusion as there is a higher ion concentration within the cell than outside. Channel proteins often have hydrophilic pores that allow the diffusion of other ions. This ensures that useful substances are able to enter the cell and that toxic substances can leave the cell.