bioc212 lecture 13 notes

bioc212 lecture 13 notes - BIOC Connexin : 4 pass...

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Connexin : 4 pass transmembrane BIOC 212 Lecture 13 General aspects of the next chapters How are the cells held together, how do they work together? Direct binding : cell-cell junctions, cell adhesion Cell surface receptors that bind cells to the matrix Extracellular Matrix : complex network of secreted molecules. Most important functions is a supporting framework Epithelial and Connective Tissues: Major tissue types in vertebrates: Nerve, Blood, Muscle , Lymphoid, Epithelial , Connective Connective Tissue: characterized by a loose arrangement of cells: fibroblasts, collagen Smooth Muscle: able to contract, important for gut function with different layers Compare connective tissues with epithelial cells Figure: Cross-sectional view of the intestinal wall: Tube-like organ is constructed from epithelial tissue (red), Connective tissue (2 nd layer), Muscle tissue (3 rd ). Each tissue organized assembly of cells held together by cell–cell adhesions, cell-extracellular matrix adhesions, or both. 1
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Classification of Cell Junctions: Summary of the different junctions 1) Occluding junctions - seal cells together in an epithelium, no leaking from one side to the other 2) Anchoring junctions - mechanically attach cells to the neighbors(actin filament) or the extracellular membrane (intermediate filament) 3) Communicating junctions - mediate the passage of signals from one cell to the next 2
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Tight junction in trans-cellular transport: in vertebrates selective transport 2 sets of proteins - no mixing tight seals and diffusion barriers Figure: The role of tight junctions in transcellular transport. Transport proteins are confined to different regions of the plasma membrane in epithelial cells of the small intestine. This segregation permits a vectorial transfer of nutrients across the epithelium from the gut lumen to the blood. In the example shown, glucose is actively transported into the cell by Na+-driven glucose symports at the apical surface (higher Na+ concentrations in the lumen), and it diffuses out of the cell by facilitated diffusion mediated by glucose carriers in the basolateral membrane. Tight junctions are thought to confine the transport proteins to their appropriate membrane domains by acting as diffusion barriers within the lipid bilayer of the plasma membrane; these junctions also block the backflow of glucose from the basal side of the epithelium into the gut lumen. 3
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Electron Microscopy (Transmission): -Wavelength of electron decreases as velocity increases -Accelerating voltage = 100,000 V => wavelength is 0.004 nm -Practical resolving power for biological specimen = 1 nm (200 x higher than light microscopes) -Source of electrons = cathode on top -Acceleration through nearby anode = Electron beam travels down the tube -Electrons become scattered by collisions with air molecules => ultralow vacuum necessary -magnetic coils focus the beams (like glass lenses in a light microscope) -Staining of specimen with electron dense material (e.g. osmium tetroxide - binds to lipid bilayers and
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bioc212 lecture 13 notes - BIOC Connexin : 4 pass...

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