The cell membrane controls the entry and exit of materials through cells. The main role of cell membranes is to: Separate the internal environment of a cell from the external environment, Act as a site for chemical interactions and energy conversions, and Detect and bind to substances and initiate biological processes. The cell membrane consists of two layers separated by a very small space of approximately 7-10 nanometers and is found in both animal and plant cells.
There are 3 chemicals found in cell membranes.
Lipids - which form the bi-layer
Proteins - consist of two types: a. those that span the whole membrane and b. those that are found embedded in the surface or lower layers
Carbohydrates - they are on the surface
Molecules may move within this flexible and dynamic membrane, this is why the membrane is termed fluid. There exists a range of different chemicals and hence the name mosaic.
The current model for the structure of the cell membrane is thus termed the fluid mosaic model.
The two types of proteins play vital roles in the functioning of the membrane. The channel proteins control the entry and exit of certain materials based on both their size and molecular composition. Surface receptor molecules are important in binding to such chemical as hormones to promote cell division or recognizing a foreign particle or antigen to alert other cells of the presence of an invader.