SimScience - Membranes - Advanced, page 6

Amphiphilic molecules in water

How do amphiphilic molecules arrange themselves in water? We have seen that in oil and water mixtures they form micelles and monolayers which keep the hydrophilic heads in water and the hydrophobic tails away from the water. Without any oil this means that the tails will tend to go next to each other to avoid the water.

Two simple arrangements allow the tails to be away from the water:

[Diagram of micelles in water]

We have seen the micelle before but the molecules can also for a double layer structure:

[Disgram of bilayer]

This arrangement is called a bilayer (*). Imagine two sheets of molecules sandwiched together so that all the hydrophilic heads on the outside (in contact with the water) and the hydrophobic tails inside (away from the water).

Just like monolayers, we say that bilayers are membranes. Bilayers are particularly interesting because of their properties and their importance in biological systems. The human body depends on many many membranes of this type.