Lecture 12 The Cytoskeleton (Microfilaments, Intermediate Filaments, and Microtubules)

Lecture 12 The Cytoskeleton (Microfilaments, Intermediate Filaments, and Microtubules)

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IPHY 3060 Lecture12: The Cytoskeleton I: Microfilaments, Intermediate Filaments, and Microtubules
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The Cytoskeleton Definition: a system of supports made of proteins within the cell that provide support and structure
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Functions of the cytoskeleton Provide structural support to cells and tissues Allow movement of cells and organelles
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3 Types of Cytoskeletal Filaments Actin filaments Intermediate filaments Microtubules
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The Different Filament Systems Have Different Distributions Actin filaments—in membrane projections, around membrane, in cables in cytoplasm Microtubules— extending through cytoplasm Intermediate filaments —surround nucleus
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The Different Filament Systems Have Different Distributions
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Actin Filaments
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Actin Filaments 5-7 nm diameter Composed of polymer of actin monomers Very dynamic—can form and unform very rapidly Have both structural and movement functions
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Structural Functions of Actin Filaments 1) Stress fibers 2) Membrane support 3) Microvilli
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Structural Functions of Actin Filaments Stress fibers —thick cables of actin filaments that provide support to the entire cell Membrane support —actin filament network underneath the cell membrane to provide it with support Microvilli —specialized membrane extrusions on cells that are packed with actin filaments to provide them with support Stress fibers Microvilli Membrane Support
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Movement Functions of Actin Filaments 1) Cell migration— movement of cells by amoeboid crawling 2) Muscle contraction- shortening of muscle fibers to produce contractile force to move joints and limbs 3) Cytokinesis—actual splitting of a dividing cell into 2 daughter cells
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Actin One of the most abundant proteins in cells One of the oldest genes in eukaryotes—found in amoeba, yeast, etc. Is a very highly conserved protein Humans have 6 actin genes—4 muscle isoforms and 2 non-muscle Monomeric actin is called G-actin
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Actin Filament Assembly
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Actin filament has polarity G-actin monomers are added to the (+) end much more rapidly and come off (–) end much more readily
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Actin Filament Assembly Step 1: nucleation or formation of small oligomers from G-actin
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Lecture 12 The Cytoskeleton (Microfilaments, Intermediate Filaments, and Microtubules)

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