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CellBio2 - T h e C y t o s k e le t o n o f E u k a r y o t...

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1 The Cytoskeleton of Eukaryotic Cells A Network of Skeletal Fibers that is Continually Changing its Shape Functions: Cell Structure and Movement The Cytoskeleton The three main kinds of fibers are: Actin filaments -also called Microfilaments, (7 nm diameter) made of the protein, actin • Microtubules (25 nm diameter) made of the protein, tubulin Intermediate filaments made of many different proteins
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2 Actin Filaments
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3 Figure 4.19 Showing Cause and Effect in Biology Actin Filaments (Microfilaments) • The filaments look like 2 inter-twined strings of beads • Occurs in bundles containing many actin filaments and in complex networks
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4 Some Important Properties of Actin Filaments They polymerize (self assemble) by noncovalent, reversible, addition of actin monomers at the ends of the filaments- are highly dynamic A fundamental capability of biological molecules is the ability to self-assemble Some Important Properties of Actin Filaments They polymerize (self assemble) by noncovalent, reversible, addition of actin monomers at the ends (tips) of the filaments (A fundamental capability of many biological molecules is the ability to self-assemble) • ATP is hydrolyzed during assembly, causing a special type of dynamic activity called treadmilling (assembly at one end of the filament and disassembly at the opposite end----the filaments are polar) There are many actin-associated proteins that tell the actin filaments how to assemble and what to do
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5 Two Main Functions of Actin Filaments • Determining cell shape and changing cell shape • Cell movement (cell motility) Movement of cells from one place to another, movements inside cells For example, making a cell long and thin or changing the shape to short and thick
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6 Three Examples of Actin Filaments in Structural Support Stress Fibers (bundles of actin filaments) help keep cells elongated and stiff
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7 Three Examples of Actin Filaments in Structural Support stress fibers (bundles of actin filaments) Fig 4.20 part A • Microvilli (relatively stable actin bundles projecting from the cell surface) increases the cell’s surface area Figure 4.21 Microfilaments for Support
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8 Cartoon Diagram of a Brush Border Microvillus Actin filaments Actin-linking proteins Epithelial Cell “Brush Borders” Fig. 4.22 Increases surface area of cells- for absorption of nutrients
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9 Three Examples of Actin Filaments in Structural Support stress fibers (bundles of actin filaments) • microvilli (relatively stable actin bundles at the cell surface that increase the cell’s surface area) • focal adhesions- places of attachment of the cytoskeleton to the cell membrane The Actin Cytoskeleton Anchors the Plasma Membrane to the Cytoplasm at Focal Adhesions Membrane anchorage through actin-associated proteins (ankyrin, spectrin) and actin
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10 Actin Filaments Microtubules See part C Microtubules • Hollow tubes (25 nm) • Made of the protein, tubulin, a dimer • Main Functions: -Maintenance of cell shape -Changing cell shape - Cell movement
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11 Microtubule Structure
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