Learning objectives 
      At the end of lecture student should be able to 
      •  Describe the structure of cell membrane
      •  Explain molecular basis of cell membrane
      •  Name different types of membrane protein
      •  Correlate functions with structure of membrane 
   Membranes (highly fluid & Dynamic structure)
 Plasma membranes form closed compartments around 
 cellular protoplasm to define cell boundaries. 
 • It shows selective permeability 
   –acts as a barrier, maintaining differences in composition 
   between the inside and outside of the cell.
   –Done by specific proteins named transporters and ion channels. 
 • The plasma membrane exchanges material with the 
  extracellular environment by 
   –Exocytosis 
   –endocytosis, and 
   –gap junctions
   Membranes (highly fluid & Dynamic structure)
 • plays key roles in cell–cell interactions and in 
  transmembrane signaling.
 • Membranes also form specialized compartments within the 
  cell. (organelles), eg, 
   –mitochondria, 
   –ER, 
   –sarcoplasmic reticulum, 
   –Golgi complexes,
   –secretory granules, 
   –lysosomes, and 
   – nuclear membrane. 
 • Membranes localize enzymes, function as integral elements
   Membranes (highly fluid & Dynamic structure)
 Changes in membrane structure affect water balance and ion 
 flux and therefore every process within the cell. 
 • Specific deficiencies or alterations of certain membrane 
  –Familial Hypercholesterolemia 
  –Cystic Fibrosis
  –Wilson’s disease
  –Hereditary Spheriocytosis
  –Metastasis of Cancer cells 
   In short, normal cellular function depends on normal 
             membranes.
 Membrane structure is 
 visible using an electron 
 microscope. 
 Transmission electron 
 microscopes (TEM) can 
 show the 2 layers of a 
 membrane. 
 Freeze-fracturing 
 techniques separate the 
 layers and reveal 
 membrane proteins.