Why phospholipids arrange themselves in a bilayer form

In this module: Introduction Glycerol and Fatty Acids Glycerolipids Calorimetry Oxidation States Phospholipids Bilayers and Membranes Other Roles 1 Other Roles 2 Bilayers and Membranes Because phospholipids have both polar and hydrophobic parts, when they are in water they will spontaneously arrange themselves into ordered structures. In the cell, the most important of these is a bilayer. As a result, phospholipids, when mixed with water, spontaneously organize themselves into a few orientations.

The one you need to understand is called a bilayer. The bilayer is a membrane that defines a sphere which you can think of as an empty cell. The most abundant class of lipid molecule found in cell membranes is the phospholipid. The phospholipid molecule's polar head group contains a phosphate group. It also sports two nonpolar fatty acid chain groups as its tail.

The fatty acid tail is composed of a string of carbons and hydrogens. It has a kink in one of the chains because of its double-bond structure. The phospholipids organize themselves in a bilayer to hide their hydrophobic tail regions and expose the hydrophilic regions to water. This organization is spontaneous, meaning it is a natural process and does not require energy. The fatty acid chains are the uncharged, nonpolar tails, which are hydrophobic.

Since the tails are hydrophobic, they face the inside, away from the water and meet in the inner region of the membrane. Since the heads are hydrophilic, they face outward and are attracted to the intracellular and extracellular fluid.

If phospholipids are placed in water, they form into micelles, which are lipid molecules that arrange themselves in a spherical form in aqueous solutions.

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