Membranes are exceedingly thin, on the order of a few nanometers. Each lipid in a bilayer has a hydrophilic region with charged or hydrogen-bonding groups, plus a hydrophobic region rich in hydrocarbons. These molecules are termed amphiphilic because they can interact favorably with both polar and nonpolar solvents. Phosphatidylcholine and other phospholipids that are the major components of many biomembranes carry two long fatty acyl chains esterified to the one and two positions of glycerol. The three position of the glycerol contains a hydrophilic phosphate diester anion.
Phospholipids spontaneously form lipid bilayers in an aqueous medium.
In a lipid bilayer the hydrophilic regions of the lipids are hydrated, and nonpolar hydrocarbon region are sequestered away from water. Bilayers are stable in water. The unfavorable interaction of the lipid hydrocarbon chains with water maintains bilayer membrane structure. Lesa Beamer has compiled a web page of lipid structures . In this experiment you will isolate and characterize phospholipids from hen or quail egg yolk.