Cell membrane

The cell membrane or plasma membrane is the outer surface of a cell and encloses the contents of the cell. The cell membrane is composed of a phospholipid bilayer studded with proteins. The phosphlipid bilayer consists of two fatty acid chains that link to two of the three carbons of a molecule of glycerol. The third carbon is attached to a phosphate group, which is in turn often attached to an alcohol. The alcohol makes the phosphate-alcohol group, or head group, hydrophilic. The fatty acid chains, or tails, are hydrophobic. This causes the hydrophilic parts to point towards each other and the hydrophilic parts to point to the extra and intracellular areas. The fluid mosaic model of the plasma membrane holds that there are two types of proteins in the phospholipid bilayer. The first is called an integral protein. These proteins are generally fixed and cannot be removed without rupturing the cell. One type of integral protein called the transmembrane protein spans the membrane, so that its surface is both on the inside and outside of the cell. A second type of membrane protein is called a peripheral protein and can easily be removed from the membrane.