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 the major advance of recent years is the
increasing understanding that the lipids and phospholipids in the membrane bilayer itself are
also metabolized to b- logically active products that can diffuse either in the cytosol or in
the m- brane bilayer to control the function of other proteins. Thus the concept of
lipid-derived second messengers is now firmly established.
