A bilayer of lipid molecules (Fig. 2.1) represents the basic building

block of the plasma membrane (Cevc and Marsh, 1987; Lasic

and Barenholz, 1996; Rappolt et al., 2004; Rappolt and Pabst,

2008; Tien and Ottova, 2003), enclosing the cell interior. The lipid

bilayer is composed of two layers of lipid molecules (Fig. 2.2)

(Israelachvili, 1997; Rappolt et al., 2004), which have a water-

soluble polar headgroup and a hydrophobic non-polar tail(s). The

water-soluble headgroup (Fig. 2.2) is usually charged, having a net

positive or negative electric charge or dipole-quadrupole moment.

The hydrophobic part of the lipid molecule usually has one or more

hydrocarbon chains and is not charged.