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Published byMartha Grant Modified over 8 years ago
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Extracellular components and connections between cells
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Plasma membrane Regulates what goes in and out of the cell… Outside of cell, there is the ECM – Extracellular matrix. Glycoproteins Collagen – forms strong fibers outside cells, 40% of protein in body Integrins – cell surface receptor proteins, bind to associated proteins attached to microfilaments of the cytoskeleton. Transmit signals between the ECM and the cytoskeleton, integrate changes inside and outside of cell.
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Figure 4.26a
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Cell junctions in animal cells Especially common in epithelial cells Tight junctions: plasma membranes tightly pressed against each other, prevent leakage of extracellular fluid across a layer of epithelial cells. Ex. Between skin cells – watertight. Desmososmes – (anchoring junctions) – like rivets, fastening to cells into strong sheets. Attach muscle cells to each other Gap junctions (like plasmodesmata in plant cells) – Communicating junctions, cytoplasmic channels from one cell to an adjacent cell. Membrane protein surrounding a pore that ions, sugars and AA pass. Ec. Heart muscle, animal embryos.
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Figure 4.27 1 m Intermediate filaments TEM 0.5 m TEM 0.1 m TEM Tight junction Tight junction Ions or small molecules Extracellular matrix Gap junction Desmosome Space between cells Plasma membranes of adjacent cells Tight junctions prevent fluid from moving across a layer of cells
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Cell wall of plants Protection, maintains shape, prevents excessive uptake of water Thicker than cell membrane Contains cellulose Primary cell wall – in young plants Middle lamella – thin layer between primary walls of cells, contain pectins that are sticky and glues adjacent cells together. When mature, the cell may reinforce the primary cell wall or add a secondary cell wall between the plasma membrane and primary wall. Ex. Wood consists mainly of secondary walls
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Figure 4.25 Secondary cell wall Central vacuole Primary cell wall 1 m Middle lamella Plasmodesmata Cytosol Plasma membrane Plant cell walls
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Cell Junctions in plant cells Plasmodesmata – in plant cells Non-living cell walls are perforated with membrane-lined channels filled with cytosol. Make cells continuous with each other. Water and small solutes pass freely from cell to cell, proteins and RNA may as well.
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