E.M. of Cell Membrane

Plasma MEMBRANE...
     
the current structural model of lipid bilayer membrane is called Fluid Moasic membrane. First codified by Singer and Nicolson in 1972, the model describes the essential features of membranes. It is a two-dimensional fluid, or liquid crystal, in which the hydrophobic integral components such as lipids and membrane proteins are constrained within the plane of the membrane, but are free to diffuse laterally. In the image shown here, two integral membrane proteins are imbedded in the membrane and help facilitate transport.
    A plasma membrane is
composed of many macromolecules including: integral proteins, peripheral proteins, glycoproteins, phospholipids, glycolipids, and in some cases cholesterol, and lipoproteins. The relative amounts of these macromolecules can vary from membrane to membrane.
   The specific proteins & lipids of membranes enhance the
funcrtional role of membranes:

   a) make membranes be protective of cell (in/out)
   
b) regulate transport in and out of cell or subcellular organelle
   
c) allow selective receptivity via transmembrane receptors that bind signaling molecules
   
d) allow cell recognition
   
e) provide anchoring sites for cytoskeletal filaments or components of extracellular matrix
             allowing cells to maintain shape and/or perhaps move to distant sites.
   
f) help compartmentalize subcellular domains or microdomains
  
 g) provide a stable site for the binding and catalysis of enzymes.
   
h) regulate fusion of a membrane with other membranes in cells via specialized junctions,
             
providing a passageway for certain molecules (gap junctions)
     
       G. Childs Membrane Site @ UTMB