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2013-10-17 19:38:15
Cell Bio

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  1. Structure of 
    Adherens Junctions
    belts that encircle the cells near the apical surface of the junctional complex

    Contain adherens, whose extracellular sections overlap with the extracellular sections of cadherins on adjacent membranes

    Calcium-dependent (due to cadherin overlap)

    Associated with actin

    the cytoplasmic domains of cadherin will interact with catenins and thus the actin of the cytoskeleton
  2. Structure of tight junctions.
    • Forms continuous sheets
    • Located at the very apical end of the junctional complex between adjacent epithelial cells
    • Make contact at intermittent points
    • -          contain integral proteins that run mostly parallel to one another and to the membrane and form continuous fibrils that completely encircle the cell
    • made of both occluding and claudin, which are present together within the linear fibrils
  3. Structure of gap junctions
    • Sites between animal cells that come very close to one another without making direct contact
    • The cleft between cells is spanned by very fine strands that are actually molecular pipelines that pass through adjoining plasma membrane and open into the cytoplasm of the other cell
    • Composed of an integral membrane protein called connexin, which can organize itself into connexons, which has six connexins arranged in a ring around the annulus
    • Tightly connected through noncovalent interactions
  4. Structure of desmosomes
    • Disc-shaped that contain cadherins with a different domain structure from those in adherens junctions
    • -          To distinguish them, they are called demogleins and desmocollins
    • Dense cytoplasmic plaque on the inner surface with intermediate filaments linked to the cytoplasmic domain of desmosomal cadherins by more proteins
    • Calcium-dependent
  5. Structure of hemidesmosomes
    • Dense plaque on the inner surface of plasma membrane with keratin-containing (intermediate filaments) extending out toward the cytoplasm
    • Consists of the protein keratin, which serve a supportive function
    • keratin filaments are linked to the ECM by membrane-spanning integrins, which transmit signals from the ECM
  6. Function of adheren junctions
    • Binds cells to its neighbor through connection of cadherins in the extracellular portions near the apical surface
    • Cells held by calcium-dependent linkages
    • Connect the external environment to the actin cytoskeleton
    • Provides a pathway for signals
  7. Function of tight junctions
    • Regulates passage
    • Impermeability to water
    • Blood brain barrier
    • Binds cells into continuous sheets
    • Transmits signals
    • Fences to maintain the polarized character of epithelial cells by blocking diffusion of integral proteins
    • Involved in signaling pathways
  8. Function of gap junctions
    • Connect cytoplasm
    • Intercellular communication
    • Nonselective but can be gated and respond to voltage or cytosolic calcium ion concentration
    • Involved in stimulation of cardiac and smooth muscle
    • Allow cells to cooperate metabolically by sharing key metabolites and coenzymes
  9. Function of desmosomes
    • Link cells across an extracellular gap
    • Its plaques serve as anchorage for looping intermediate filaments
    • Structural continuity and tensile strength
  10. Function of hemidesmosomes
    • Anchors the basal layer to the underlying basement membrane
    • Transmits signals
  11. Location of adheren junctions
    near the apical surface of cells
  12. location of tight junctions
    epithelial cells
  13. location of gap junctions
    animal cells
  14. location of desmosomes
    in cells under mechanical stress, such as the cervix
  15. location of hemidesmosomes
    inner surface of the plasma membrane