Cell membranes are not, as once believed, inert structures designed to contain the cell contents, but are in fact dynamic structures that are as me- bolically active as the cytosol and other cellular compartments they surround. Thus membranes not only contain mixtures of lipid and phospholipids, but also many proteins both embedded deeply within the membrane structure itself and also more loosely attached on the membrane surfaces. Though many such proteins have long been known to act as transport proteins, ion channels, hormone receptors, G proteins, cytoskeletal anchorage points, and so on,...