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Ch. 19 - Cell Junctions, Adhesions & Extracellular Matrix A summary of the chapter and lecture notes on the cell junction, adhesions, and extracellular matrix. Includes illustrations and graphics from the textbook.

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York University
BIOL 2021
Julie Clark

BIOL 2021- May 12 2009 CHAPTER 19: CELL JUNCTIONS, ADHESION AND EXTRACELLULAR MATRIX Architecture  Cell junctions  Cell adhesion  Extracellular matrix=ECM  Proteins and polysaccharides secreted by cells Figure 19.1:architecture of animal tissue Building strategies 1) Few cells in ECM  Used in connective tissue; matrix of fibrous polymers causes stress 2) Cell-cell adhesion and cytoskeleton - Cytoskeleton is prominent  Used in epithelial cells on basal lamina (thin ECM) - Stress carried by cytoskeleton CELL JUNCTIONS Figure 19.2: classification of junctions 1) Anchoring junction - Cell to cell adhesion - Cell-matrix adhesion - Purpose is to transmit stress - Tethered to cytoskeleton 2) Occluding junctions - Seals up gaps between epithelial cells 3) Channel forming junction - Links cytoplasm of neighbouring cells 4) Signal relaying junction - Found in nerve cells - Relays signal between cells *** TABLE 19-1: CLASSIFICAION OF CELL JUNCTIONS OCCULUDING JUNCTIONS Figure: tight junctions in transcellular transport - Trans cellular transport - Tight junctions in epithelial cells - 60% of all cell types= epithelium - In epithelium cells, cells are polarized=  Basal side: anchored  Apical side: free - Tight junctions keep transport proteins segregated  Sodium can diffuse across tight junctions Figure: a) sealing strands in tight junctions b) claudins in tight junctions - Structure in tight junction  Row of sealing strands Figure: TEM of tight junctions - Proteins= claudin, adhesion protein CHANNEL FORMING JUNCTION Figure: diagram of gap junction and EM of gap junctions (freeze fraction) - Forms channels between cells - Gap junction- animal cells\ - Channels allow small molecules to pass as if the cytoplasm of cells is connected (passive) - Cells coupled metabolically and electrically (sharing between cells) - Channel proteins= CONNEXINS - 6 subunits= connexion - Two connexins to make whole channel Regulation of gap junction Fig. Regulation of gap junctions - Open or closed - Fig 19-37: neurons connected to gap junctions with fluorescent dye (a); shut gap junctions (b) can stop coupling - Functions: a) electrical coupling between neuron  Fast response b) Coordinate contraction of muscles  Heart, smooth muscle c) Also used for metabolic coordination  Cells in tissues-liver SIGNAL RELAXING JUNCTIONS - Synapse - Ion channels, signal receptors, regulatory proteins (kinases), docking proteins - Cell-cell adhesion proteins - Scaffold proteins (let other proteins stick to it) - Cytoskeleton ANCHORING JUNCTIONS Fig. Adhesion proteins ***table 19-2 anchoring junctions Fig. Cell junctions in epithelial - Transmembrane adhesion proteins that contact cytoskeleton and anchoring proteins (adapter proteins that connect) - Cadherin= cell to cell - Integrins= cell to ECM Cadherins  Cell- cell adhesion molecules  Large family of proteins found in all multicellular animals in almost all cells  All cell types  Necessary for sticking cells together  Plants don’t have cadherins  Cadherin domains are similar between cadherin proteins Fig. Cadherin family  R
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