The lipids making up a cell membrane or lipid bilayer are amphipathic, and in this lesson a section of a bilayer will be constructed using phosphotidylcholine (PC). The molecular images used in this exercise were obtained from a site developed by Angel Herráez.

One leaflet of the bilayer can be formed by aligning PC molecules next to one another, and below this has been done with 20 molecules of PC.

Adding another leaflet so that the hydrophobic ends of the PC lay next to each other gives a slice of a bilayer two PC wide. Several layers of water (red and white) has also been added to the two hydrophilic edges of the bilayer.

The image shown below is a wider slice of a bilayer with a potion of the water removed from the one edge of the bilayer. Notice that in the two structures above and the one below that the components of the bilayer are evenly aligned as the components of a crystal would be. You can observe this phenomena by slowly rotating the structures and noticing that at certain locations the hydrocarbon chains will align with each other.

When rotating the structure below, you will notice that very few of the components align as in the above structures. This feature emphasizes that the bilayer is not a highly ordered structure and that it is fluid or quasi-fluid in nature.