1. Chapter 18
Cell Junctions, Cell Adhesion, and the Extracellular Matrix

2. A cross-sectional view of part of the wall of the intestine
Cell junctions
to adjacent cells
or Basal lamina
Rich in ECM

3. Cell junctions:
Occluding junctions--seal cells together, prevent even small
molecules from leaking from one side of the sheet to the other;
Anchoring junctions--mechanically attach cells and their
cytoskeleton to their neighbors or to the extracellular matrix;
Communicating junctions--mediate the passage of chemical
or electrical signals from one interacting cell to its partner

4. The role of tight junctions in transcellular transport
The structure of a tight junction
Diffusion barrier
Sealing strands:
a long row of
transmembrane adhesion
proteins
Claudins
Occludins
ZO (zonula occludens):
anchor the strands to actin
cytoskeleton

5. Septate junctions: occluding junctions in invertebrates
More regular a structure
A continuous band around each epithelial cell
Parallele rows of junctional proteins:regular periodicity
Discs-large in fly in related to ZO

6. Anchoring junction:connecting cytoskeleton to a neighbor or to the ECM
Adherens junctions and desmosomes: among cells-cadherins
Focal adhesions and hemidesmosomes-integrins
Actin filaments
Intermediate filaments

7. Adherens junctions
Actin bundles are linked via the cadherins and anchor proteins
into an extensive transcellular network
Adhesion belt
contractile

8. Desmosomes connect intermediate filaments from cell to cell
Buttonlike
Pemphigus: autoimmume disease-antibodies bind to and disrupt
the desmosomes-blistering of the skin with leakage of body fluid
into the loosened epithelium

9. Focal adhesion actin vinculin Muscle cells attach to
their tendons this way

10. Desmosomes and hemidesmosomes
integrins

11. Gap junction
Gap!
Electrical and chemical coupling

12. Summary of cell juctions in a vertebrate epithelial cell

13. Plasmodesmata are the plant gap junctions
Plant don’t need anchoring junctions

14. Cells assemble to form a tissue

15. The structure and function of cadherins
Calcium-dependent
Homophilic

16. E-cadherin
N-cadherin
Cadherin-7 in ganglion cells from neural crest cells

17. Three ways cell-surface molecules can mediate cell-cell adhesion
Cadherin-dependent
cell sorting

18. Selectins mediate transient cell-cell adhesions in the bloodstream
Calcium-dependent
Carbohydate-binding proteins (lectins)
Binding of white blood cell
to endothelial cells

19. Immonoglobulin
superfamily proteins
mediate Calcium-independent
cell-cell adhesion

20. Summary of the junctional and nonjunctional adhesive mechanisms

21. The repeating disaccharide sequence of dermatan
sulfate glycosaminoglycan (GAG)
Negatively charged
ECM: polysaccharide chains GAGs linked to protein(proteoglycans)
And fibrous proteins (collagen, elastin, fibronectin, laminin)

23. A model of the molecular structure of a basal lamina

24. Dog aorta
Covalent bonds
Stretch and recoil
like a rubber band
Five times more extensible

25. Plant cell walls are made of polysaccharide cellulose,
the most abundant organic macromolecule on earth
Long unbranched chains
Of b1,4-linked glucose
uints

26. Summary Three types of cell junctions: structure and function
Cell adhesion has important role in development and
function
Two main types of ECM molecules:
proteoglycans and fibrous proteins