Cell Biology: Cell Surface and Communication Part II

Cell Adhesion

• Two forms of interactions allow cells to aggregate into distinct tissues and provide a means for transfer of information between the interior and exterior of cells
  
• Cell-Adhesion Molecules (CAMs) source
  
• Allow cells in tissues to directly adhere to one another (cells of the same type, homotypic adhesion, or cells of different types, heterotypic adhesion)
• A CAM can directly bind to the same kind of CAM on an adjacent cell (homophilic binding) or to a different class of CAM (heterophilic binding)
• Cell-cell adhesions can be long lasting (nerve cells) or very weak (immune-system cells that roll along vessels)
  
• Four major families
• Cadherins, Ig superfamily, Selectins, Integrins
  
• Adhesion Receptors
  
• Adhere cells to the ECM

Cell Junctions

• Serve several functions
• Junctions impart strength and rigidity to a tissue
• Transmit information between the extracellular and intracellular space
  
• Control the passage of ions and molecules across cell layers
  
• Serve as conduits for the movement of ions and molecules from the cytoplasm of one cell to that of its neighbor
• Three major classes
• Anchoring Junctions and Tight Junctions
  
• Hold cells together into tissues
• Organized into three parts
• Adhesive proteins (CAMs and adhesion receptors)
• Adapter proteins (connect CAMs or adhesion receptors to cytoskeletal filaments and signaling molecules)
• Cytoskeletal Filaments
• Tight Junctions control the flow of solutes between cells forming an epithelial sheet
  
• Gap Junctions
• Permit rapid diffusion of small, water-soluble molecules between the cytoplasm of adjacent cells
• Contains clusters of channels between two plasma membranes separated by a gap