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Chapter 18 Cell Junctions, Cell Adhesion, and the Extracellular Matrix
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A cross-sectional view of part of the wall of the intestine
Cell junctions to adjacent cells or Basal lamina Rich in ECM
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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
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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
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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
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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
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Adherens junctions Actin bundles are linked via the cadherins and anchor proteins into an extensive transcellular network Adhesion belt contractile
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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
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Focal adhesion actin vinculin Muscle cells attach to
their tendons this way
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Desmosomes and hemidesmosomes
integrins
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Gap junction Gap! Electrical and chemical coupling
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Summary of cell juctions in a vertebrate epithelial cell
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Plasmodesmata are the plant gap junctions
Plant don’t need anchoring junctions
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Cells assemble to form a tissue
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The structure and function of cadherins
Calcium-dependent Homophilic
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E-cadherin N-cadherin Cadherin-7 in ganglion cells from neural crest cells
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Three ways cell-surface molecules can mediate cell-cell adhesion
Cadherin-dependent cell sorting
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Selectins mediate transient cell-cell adhesions in the bloodstream
Calcium-dependent Carbohydate-binding proteins (lectins) Binding of white blood cell to endothelial cells
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Immonoglobulin superfamily proteins mediate Calcium-independent cell-cell adhesion
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Summary of the junctional and nonjunctional adhesive mechanisms
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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)
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A model of the molecular structure of a basal lamina
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Dog aorta Covalent bonds Stretch and recoil like a rubber band Five times more extensible
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Plant cell walls are made of polysaccharide cellulose,
the most abundant organic macromolecule on earth Long unbranched chains Of b1,4-linked glucose uints
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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
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