Phospholipid Bilayers.

Phospholipid are molecules that have a region that is composed of polar atoms (that prefer to interact with water molecules), and region which is composed of apolar atoms (which have a reduced solubility in water). These types of molecule which have polar and apolar regions are called amphiphilic, and have a tendency to aggregate when placed in water. As shown in the diagram below, the aggregates of phospholipids are highly organized, and the apolar, or hydrophobic region of the molecules are packed closely together, which results in the exclusion of water molecules. In contrast, the polar atoms are arranged along the outside of the aggregate and are in full contact with the aqueous surroundings. This means that in a bilayer structure, both parts of the phospholipid molecules are in their preferred environments. This type of organization gives the phospholipid bilayer structure a high degree of stability in water.

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