The Cell Membrane

Anatomy of  The Cell Membrane

All living cells are surrounded by a cell or plasma membrane which form a barrier between the interior and exterior of cells. The cell membrane:

·         Regulates what enters and exits a cell

·         Consist of the structural units; phospholipids which forms a bilayer(a double layer). The hydrophilic heads of phospholipids are exposed to the watery exterior and watery interior of cell. The hydrophobic tails of phospholipids face each other in the middle.

·         Is fluid because the phospholipids are free to move around (though their movement is restricted by cholesterol) and the bilayer is interspersed with many proteins forming a mosaic pattern. The structure of the cell membrane is therefore described by the fluid mosaic model proposed by S.Singer and G.Nicolson. The Fluid Mosaic Model is shown below:

 

Component of Cell Membrane	Function
Phospholipid bilayer	Prevents loss of important watersoluble molecules as they cannot pass the hydrophobic layer.
Channel Protein (Transmembrane protein –spans membrane)	Provide a passage for transport of polar molecules and ions across membrane.
Carrier Protein (Transmembrane protein)	Transports molecules across membrane via a series of conformational changes.
Receptor Protein (Transmembrane protein)	Transmit information into cell by providing a specific binding site for a specific molecule or substrate.
Glycolipids (carbohydrate  attached to phospholipid)	Responsible for tissue recognition they form A,B,O blood group markers.
Glycoproteins (carbohydrate  attached to protein)	Prevents one’s immune system from attacking its own cells as they form the major histocmpatability complex protein.
Cholesterol (dispersed throughout membrane)	Stabilize membrane structure by restricting movement of phospholipids.

Table Listing The Functions of the different Components of the Cell Membrane