BIS104 Note12

BIS104 Note12 - Lecture 12 Bio Sci 104 Winter 2010 Cell...

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Lecture 12 1 Bio Sci 104 Winter 2010 Cell junctions IV. Types of anchoring cell-cell contacts (Anchoring junctions) A. After the initial cell-cell or cell-extracellular matrix recognition occurs, this can become formalized into specific, cell-cell anchoring contacts. These contacts permit cell-cell communication, and contribute to the strength of tissues and organs . Three main kinds in animal cells: tight junctions, anchoring junctions, and channel-forming (communicating) junctions . B. Tight junctions in vertebrates (occ lud ing junct ions) . Form a permeab i l ity barr ier across epithelial cell sheets. e.g. the epithelial lining of the small intestine consists of cells pumping glucose out of lumen of gut on apical (gut lumen) surface, yet permitting diffusion of glucose from basolateral surface into blood stream. Tight junctions keep the two different membrane transporters segregated on apical and basolateral sides of cells, and prevent glucose from diffusing between cells back into gut lumen. The tight junctions in different tissues can have different permeability properties. Exact structure unclear, appear to represent belts of web-like material consists of claudins, occludin, ZO protein, with increasing impermeability with increasing number of belt strands. (FYI: In invertebrates- septate junctions.) C. Anchoring junctions : serve as links between the cytoskeleton elements of one cell to those of another; thus , t ie together ce l ls as a structura l un it . Found most in tissues under mechanical stress (e.g. heart muscle, skin). Made of transmembrane linker proteins, which on cytoplasmic side are joined to cytoskeleton by intracellular attachment proteins. Three kinds of anchoring junctions: 1. (a). adherens junctions : connect bundles of actin filaments from cell to cell. Cell-cell linkages consist of transmembrane cadherins wh ich l
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BIS104 Note12 - Lecture 12 Bio Sci 104 Winter 2010 Cell...

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