Expert: John Locke - 8/26/2007

Question
How do phospholipids interact with water to form lipid bilayers?

Answer
Thanks for using AllExperts, DeAva.

Phospholipids don't interact with water in a chemical fashion--that is, there is no chemical reaction in the process of forming a lipid bilayer. The phosopholipds instead seek out the most stable spatial arrangement possible (technically speaking, this is a thermodynamically-driven process). These molecules, as you know, have a hydrophobic end (the lipid tail) and a hydrophilic end (the phosphate head); the hydrophobic end is unstable when exposed to water. To compensate for this, the phospholipids arrange themselves in the fashion that you're probably familiar with: phosphate head groups grouped toward the aqueous phase (forming an "inside" and "outside" of the bilayer) with the lipid tails toward the center. In doing so, the phosphate heads "see" only an aqueous environment, and the lipid tails "see" only a hydrophobic environment. The bilayers themselves have distinct characteristics that depend upon the temperature, the nature of the tails and heads, solvent, etc.; no matter what the external conditions, however, the phospholipids always interact so as to sequester the hydrophobic ends away from the aqueous phase.

The phospholipid bilayer arrangment is usually the most energetically stable conformation possible for the molecules. No energy is required to form a bilayer--the process is spontaneous.

Here's a site that explains this in a bit more detail. Good luck!


http://www.sparknotes.com/biology/cellstructure/cellmembranes/section1.html