The bilayer above contains a hundred or so phosphatidyl cholines, which are very amphipathic phospholipids; each of these consists of a glycerol backbone, two acyl residues and phosphoryl choline residue.  The hydrocarbon chains are non-polar and very hydrophobic, while phosphoryl choline is charged and very hydrophylic. The acyl residues are colored different shades of muted grey and green and constitute the core of the bilayer.  The oxygens forming the various ester linkages and associated with the phosphate groups are colored red while the phosphorous atoms themselves are orange and the choline nitrogens, blue.  Along its outer surfaces, the bilayers of wet liposomes are flanked by hundreds of water molecules, here depicted by lime green oxygen atoms (with invisible hydrogens).

The image was constructed with RasMol by Eric Martz, University of Massachusetts, using "Protein" Data Base (PDB) coordinates obtained by x-ray crystallography by Heller, et al. (1993 J Phys Chem 97:8343).