Adhesion Junctions

Six subunits of a connexon Desmosome Hemidesmosome tight junction

Cell - Cell Adhesions


  1. Cell surface molecule protein: Integrin
    1. Binds and mechanically fixes cells to ECM
    2. Serves in signal transduction also
    3. At focal adhesion --> it is part of the Focal Adhesion Kinase Pathway
      1. triggers cell anchoring
  2. Cell adhesion molecules: CAM's; usually glycoproteins
    1. Cadherens: calcium dependent
      1. important in initial attachment such as in development of cells, and maintaining the structure and integrity of cells
    2. Selectins
    3. Ig superfamily
      1. N - CAM's, nerve cells and calcium independent

Cell Junctions


  1. Occluding junctions: "Tight" in epithelial sheets
    1. Maintenance of selective permeability
    2. Prevention of protein migration
  2. Anchoring junctions
    1. cytoskeleton --> cytoskeleton
    2. cytoskeleton --> ECM
    3. Adherens junctions: involved in actin connections
      1. actin --> actin
      2. actin --> matrix
    4. Desmosomes: intermediate filaments
      1. cell --> cell
    5. Hemidesmosomes: intermediate filaments --> ECM
  3. Communicating junctions (Gap junctions)
    1. Allow for small molecules to pass from cell --> cell (less than 1000 daltons)
      1. six subunits form a connexon or a pore
      2. has an intercellular gap of approximately 2nm
      3. electrically excitable cells
      4. helpful in responces to second messenger signals, like CAMP
      5. gradient hypothesis of development