Phospholipids are Like Triglycerides with a Phosphate Group

Phospholipids serve an extremely important function in our bodies, they form the cell membrane. Think of each cell as being surrounded by a fence, a fluid fence, but a fence none the less. It is called the the cell membrane or the plasma membrane. The cell membrane is composed of two layers, each composed of trillions of Phospholipid molecules oriented in a special manner.

Phospholipids are very much like triglycerides but with one important difference. A phosphate functional group is substituted for one of the three fatty acids.

The image on the left shows three different ways to depict Phospholipids. The glycerol portion of the molecule is shown in red in the Fisher drawing (atoms represented by letters). The two fatty acids are below the red and the phosphate group (with some methyl and amino decorations) is above. You may also notice that j one of the fatty acids is saturated and the other, unsaturated.

The most important feature of phospholipid structure is that the fatty acid "tails" are non-polar while the phosphate "head" is very polar. This leads to a chemically confused (solubilty-challenged) molecule. When exposed to an aqueous (water) environment, phospholipids form unique assemblies called "bilayers". The polar heads of the P-lipids turn toward the water molecules (Hydrophilic) while the non-polar tails hide from water molecules (Hydrophobic).

The structure that surrounds each of your cells (the plasma or cell membrane) is formed from a Phospholipid bilayer. The polar heads of the phospholipids are all facing the aqueous environments of the outside, and the inside of the cell, while the non-polar tails form a fatty layer on the inside This structure is an important barrier and defines the boundaries of living and unliving portions of a cell.

The two-celled human embryo in this image looks like two bubbles stuck together. The Phospholipid bilayer (membrane) is flexible, much like like a bubble, continually moving and flowing. The phospholipids are held together by only by weak hydrogen bonds of the heads and the even weaker interactions between the hydrophobic lipid molecules in the tails.