chapter 18 cell junctions, cell adhesion, and the extracellular matrix
TRANSCRIPT
Chapter 18
• Cell Junctions, Cell Adhesion, and the Extracellular Matrix
Rich in ECM
Cell junctions to adjacent cells or Basal lamina
A cross-sectional view of part of the wall of the intestine
Cell junctions:
1. Occluding junctions--seal cells together, prevent even smallmolecules from leaking from one side of the sheet to the other;
2. Anchoring junctions--mechanically attach cells and theircytoskeleton to their neighbors or to the extracellular matrix;
3. Communicating junctions--mediate the passage of chemicalor electrical signals from one interacting cell to its partner
The role of tight junctions in transcellular transport
Diffusion barrier Sealing strands:a long row of transmembrane adhesionproteins
ClaudinsOccludins
ZO (zonula occludens):anchor the strands to actincytoskeleton
The structure of a tight junction
Septate junctions: occluding junctions in invertebrates
More regular a structureA continuous band around each epithelial cellParallele rows of junctional proteins:regular periodicity
Discs-large in fly in related to ZO
Anchoring junction:connecting cytoskeletonto a neighbor or to the ECM
Adherens junctions and desmosomes: among cells-cadherinsFocal adhesions and hemidesmosomes-integrins
Actin filamentsIntermediate filaments
Adherens junctions
Actin bundles are linked via the cadherins and anchor proteinsinto an extensive transcellular network
Adhesion belt
contractile
Desmosomes connect intermediate filaments from cell to cell
Pemphigus: autoimmume disease-antibodies bind to and disruptthe desmosomes-blistering of the skin with leakage of body fluidinto the loosened epithelium
Buttonlike
Focal adhesionactin vinculin
Muscle cells attach to their tendons this way
Desmosomes and hemidesmosomes
integrins
Gap junction
Electrical and chemical coupling
Gap!
Summary of cell juctions in a vertebrate epithelial cell
Plasmodesmata are the plant gap junctions
Plant don’t need anchoring junctions
Cells assemble to form a tissue
The structure and function of cadherins
Calcium-dependentHomophilic
E-cadherin
N-cadherin
Cadherin-7 in ganglion cells from neural crest cells
Three ways cell-surface molecules can mediate cell-cell adhesion
Cadherin-dependentcell sorting
Selectins mediate transient cell-cell adhesions in the bloodstream
Calcium-dependentCarbohydate-binding proteins (lectins)
Binding of white blood cell to endothelial cells
Immonoglobulin superfamily proteinsmediate Calcium-independentcell-cell adhesion
Summary of the junctional and nonjunctional adhesive mechanisms
The repeating disaccharide sequence of dermatansulfate glycosaminoglycan (GAG)
Negatively charged
ECM: polysaccharide chains GAGs linked to protein(proteoglycans)And fibrous proteins (collagen, elastin, fibronectin, laminin)
A model of the molecular structure of a basal lamina
Dog aorta
Covalent bonds
Stretch and recoil like a rubber band
Five times more extensible
Plant cell walls are made of polysaccharide cellulose,the most abundant organic macromolecule on earth
Long unbranched chainsOf 1,4-linked glucoseuints
Summary
1. Three types of cell junctions: structure and function2. Cell adhesion has important role in development and
function3. Two main types of ECM molecules:
proteoglycans and fibrous proteins