Permeability Properties of Unmodified Lipid Bilayer Membranes

Biological membranes are dynamic, mosaic structures where different transport functions usually occur simultaneously. The molecular mechanisms responsible for the transmembrane movement of solutes, ions or nonelectrolytes, are therefore only understood in part, due to the difficulties in isolating and identifying the properties of particular transport systems — whether in situ or in vitro. Much of the available information has been obtained in a few particularly simple biological systems. Most of the conceptual knowledge, however, has been obtained in studies on artificial model membranes.