Set2.Dr._Wilson_MCDB1A.2010

Set2.Dr._Wilson_MCDB1A.2010 - The Cytoskeleton A Network of...

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The Cytoskeleton A Network of three different kinds of Skeletal Fibers Functions: Cell Structure and Movement Actin Filaments/Microfilaments (7 nm diameter) Microtubules (25 nm diameter) Intermediate filaments (10 nm diameter)
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Figure 5.17 The Cytoskeleton
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Some Important Properties of Actin Filaments They assemble and disassemble by noncovalent, reversible, addition/loss of actin monomers at the ends of the filaments • ATP is hydrolyzed, causing a type of dynamic activity called treadmilling (assembly at one end of the filament (the plus end) and disassembly at the opposite end (the minus end) •The ends do not have different charges!!
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Two Main Functions of Actin Filaments 1. Determining cell shape 2. Cell movement (cell motility) - such as, movement of cells from one place to another
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Examples of Actin Filaments in Cell Shape “Stress Fibers” (bundles of actin filaments) help keep cells elongated
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Figure 5.17 The Cytoskeleton (Part 1)
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Examples of Actin Filaments in Structural Support •microvilli ( stable actin bundles projecting from the cell surface) increases the cell’s surface area
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Figure 5.19 Microfilaments for Support
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Examples of Actin Filaments in Structural Support focal adhesions - places where the actin cytoskeleton attaches to the cell membrane
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The Actin Cytoskeleton Anchors the Plasma Membrane to the Cytoplasm at Focal Adhesions Membrane anchorage through actin-associated proteins
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Cell movement
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Figure 5.18 Microfilaments and Cell Movements
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Microtubules • Hollow tubes 25 --nm diameter • Made of tubulin dimers (one molecule of alpha tubulin and one of beta tubulin) alpha beta Tubulin dimers
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Figure 5.17 The Cytoskeleton (Part 2)
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Microtubules Like actin filaments, the two ends of microtubules have different properties One end is called the plus end , the opposite end is called the minus end
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Microtubules • Main Functions (also like actin filaments): 1. Cell Shape 2. Cell movement but different kinds of shapes and movement than with actin filaments
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Microtubules carry out two types of dynamics Dynamic Instability - switching between growth and shortening at microtubule ends Treadmilling (same as actin filaments) - growth at plus ends and shortening at the minus ends
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Microtubules are “organized” in cells at “Microtubule Organizing Centers” (MTOCs) also called “ centrosomes In animal cells, they are found near the nucleus and consist of a stable pair of centrioles that is surrounded by an ill-defined “ pericentriolar matri x” Centrioles are barrel shaped arrangements made of 9 sets of triplet microtubules
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