Self-Assembly of a Membrane

The video below shows a computer simulation of the self-assembly of a lipid bilayer.  Specifically, it simulates what happens when the phospholipid Dipalmitoylphosphatidylcholine (DPPC) is exposed to water.  DPPC acts very much like the surfactants described in Section 8.4 of Biological Physics as each molecule of DPPC has a polar (hydrophilic) head and a hydrophobic tail.  When this substance is placed in water, the molecules arrange themselves so that the hydrophobic tails point toward each other and only the polar heads come in contact with the water.  The result of the natural tendency to arrange in this manner is alternating “layers” of phospholipid and water.  The phospholipid layers are called bilayers because they consist of two rows of DPPC molecules with their tails facing one another.  Most cell membranes are made of a very similar lipid bilayer.  Ultimately, these membranes are able to self-assemble because of the chemical properties of the molecules they consist of.