Cytoskeleton III

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Cytoskeleton III

• Chapter 16

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Actin binds to many different proteins
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Plectin (green) crosslinks intermediate filaments
(blue) and microtubules (red)?
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Cross linking proteins organize different
assemblies of actin filaments
actin binding sites in red
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Actin bundles in a microvillus
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Filamin crosslinks actin into 3-dimensional
networks with gel-like properties
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Melanoma cells with low filamin levels crawl
poorly and tend not to metastasize
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When filamin levels are restored the cells move
normally and become highly metastatic
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Three stages in control of bleeding
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Severing existing actin filaments can accelerate
assembly of new filaments
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Gelsolin severs actin filaments
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Actin filament dynamics and platelet activation
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Actin filament dynamics and platelet activation
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Platelets prior to activation
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Activated platelet with large spread lamellipodium
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Activated platelet after contraction
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Aggregation of platelets
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Thrombin is produced at cell surface of platelets
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Ca2 and diacylglycerol activate protein kinase C
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Fibrin emerging from clump of activated platelets
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ERM proteins attach actin to plasma membrane
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Actin fibers often terminate at focal points
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Extracellular signals can effect actin
organization, vinuculin identifies focal contacts
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Extracellular signals can effect actin
organization
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Extracellular signals can effect actin
organization
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Extracellular signals can effect actin
organization
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Structure of myosin II
Myosin head binds and hydrolyzes ATP
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Electron micrograph of myosin molecules
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Myosin is arranged in thick filaments
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Myosin heads are on outside of thick filament
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Motor activity is contained completely within
myosin heads
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Myosin heads can move actin filaments
Speed of 4 micrometer per sec
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Attached, no ATP
Rigor configuration, state acquired during rigor
mortis
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ATP binding causes release of actin filament
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Hydrolysis of ATP causes displacement of head by
5 nm
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Release of Pi causes tight binding to new
position on actin filament
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ADP is released and rigor configuration is
assumed once again
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Mechanochemical cycle of myosin
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DVD clip 74