3 - Extracellular Matrix & Cell-Cell Connections

3 - Extracellular Matrix & Cell-Cell Connections -...

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Lecture 3: Structure of extracellular matrix and cell-cell connections The making and breaking of attachments are important events in the lives of cells and provokes large changes in their internal affairs Molecular Biology of the Cell 5
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In multicellular organisms cells have to attach to extracellular space and each other and communicate
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QuickTime™ and a  decompressor are needed to see this picture. Manual of the Infusoria 1880-1882 Choanoflagellates (unicellular organisms) Choanocytes (cells inside sponge) QuickTime™ and a  decompressor are needed to see this picture. Nicole King, Dev. Cell 2004 Multicellular algae appeared about 1.0 Multicellular animals appeared about 0.6 Bya Unicellular organisms have been present on the Earth for over 3.5 Bya Multicellularity: Benefits and Costs ? Origin of multicellularity
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Extracellular space Two types: basal lamina and space found in connective tissues (bone, tendon etc) Figure 19-1 Molecular Biology of the Cell (© Garland Science 2008) Figure 19-40 Molecular Biology of the Cell (© Garland Science 2008)
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Figure 19-42a Molecular Biology of the Cell (© Garland Science 2008) Basal lamina underlie all epithelia and composed of laminin and type IV collagen Figure 19-43 Molecular Biology of the Cell (© Garland Science 2008) Laminin and type IV collagen form networks that connected by other proteins
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mechanical support interface and attachment between epithelia and connective tissue barrier between compartments influence cell polarity and differentiation guide cell migrations and regeneration Functions of basal lamina Figure 19-44 Molecular Biology of the Cell (© Garland Science 2008) Figure 19-39 Molecular Biology of the Cell (© Garland Science 2008)
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Extracellular matrix of connective tissues Figure 19-53 Molecular Biology of the Cell (© Garland Science 2008) Need to provide mechanical structure to resist two types of forces: compressive forces and stretching forces Main components of ECM: - glycosaminoglycans (GAG) : compressive forces - proteins (collagen, elastin): stretching forces How ECM can resist compressive forces ?
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GAGs are long polysaccharides that are highly negatively charged Because of negative charge (attracts Na+) and because they hydrophilic GAGs adopt extended conformations that occupy large volume and make large amounts of water to be sucked in the matrix. This creates a swelling pressure that resist compressive forces. Figure 19-57 Molecular Biology of the Cell (© Garland Science 2008)
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wo types of GAGs: hyaluronan and proteoglycan Hyaluronan : very long (up to 25,000 disaccharide units) and simple (all disaccharide units are identical) Hyaluronan are not linked to any protein and produced directly from the cell surface Other polysaccharides dominate ECM in invertebrates and fungi (chitin) and plants (cellulose) Proteoglycans : covalently attached to proteins Proteoglycans are highly heterogeneous, even single core protein can have different attached
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3 - Extracellular Matrix & Cell-Cell Connections -...

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