Figure 1

Lipid structures and phases. (a) The structure of the major glycerophospholipids phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI), which differ only in the group indicated by X. Yellow indicates the hydrophobic tail; orange indicates the charged headgroup, which can be anionic or, where there is a positive and a negative charge, zwitterionic. (b) Lipids with a cylindrical shape, such as PC, pack as bilayers. (c) Lipids with a conical shape, such as PA or PE, pack in curved structures such as the hexagonal H_II phase.