Actin and Microtubles

Nucleotide free state binds tightly to mt leading

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Nucleotide free state binds tightly to MT Leading head binds ATP Conformational change to linker to point forward, dock and thrust trailing head forward Leading head binds MT and releases ADP, inducing trailing head to hydrolyze ATP to ADP + Pi Pi released and trailing head dissociates 31
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Myosin and Kinesin are structurally similar 32
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Kinesin motors serve diverse functions 33
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How can actin dynamics and myosin motors propel cell movements? Cell Motility Why do cells move? Single-celled organisms food prey avoidance Cells within a multicellular organism wound healing infection development disease 34
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Mechanics of Cell Movement Cell has polarity 1) Extension- membrane protrusions form at leading edge powered by actin polymerization 2) Adhesion- Membrane protrusions stick to the substratum by formation of focal adhesions 3) Translocation- Cytoplasm from rear of cell streams to front due to myosin II-mediated contraction in rear of cell 4) De-adhesion and endocytic recycling Focal adhesions in rear of cell are detached Membrane and FA are endocytosed and recycled to front for formation of new FA 35
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Microfilament structure different at leading and lagging edges 36
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Streaming of Actin and Cytoplasm in Motile Cell 37
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Microfilament structure different at leading and lagging edges Stress fibers F-actin oriented in parallel bundles Organized by formin (actin nucleating protein) Bound to integrins forming focal adhesions Myosin II contractions push cytoplasm forward Leading edge Meshwork of F-actin Dynamic network Organized by Arp 2/3 Myosin I “dragging” membrane 38
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Branching of microfilaments aid in forward movements How does actin polymerization help move a cell? Network forms via Arp2/3 A ctin-R elated P rotein Binds to F-actin at a 70° angle Nucleates formation of new actin filament Forms a meshwork to move entire cell, not just finger-like projections 39
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Adaptor proteins link actin network to plasma membrane Leading edge Lagging edge Membrane-tethered G-proteins localize actin cytoskeleton to front or rear of cell Leading edge Arp2/3 associated proteins bind to membrane-anchored G-protein Lagging edge Formin binds to membrane-anchored G- protein and actin filament 40
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Nucleotide free state binds tightly to MT Leading head...

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