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Midterm 2 Microfilaments actin.docx

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Western University
Biology 2382B
Robert Cumming

Microfilaments (Actin Filaments) 7-9nmActin Polymerization and Critical Actin Assembly -Cell Shape and function; found at cortex- Concentration -Start with nuclei; elongation occurs faster outside, just underneath plasma membrane -G actin must be in ATP form to polymerize -Form nuclei; nucleation step, steady state -Cortical Function; associated with membr-neydrolysed into ADP form-catches up reached slower -Cell movement, migration, endocytosis, etcterwards like tubulin and GTP -More polymerization at (+) end -(+) and (-) ends have different critical -Monomer: G actin (globular) concentrations: 4 lobes with a notch for ATP binding; makes it (+) end 0.12μm polar (-) end 0.6μm -Polymer: F-actin (Filamentous) microfilamWnthen in between the two Cc; adding to(+)side Double Helix; 1 turn=36nm and removing from (-) end (tread milling) Can add Myosin S1; arrow heads point to (-) end Actin Polymerization Regulation Thymosin- bound to free G actin in cell; must release to polymerize Profilin-Promotes actin polymerization by changing G-ADP to G-ATP Cofilin-Depolymerizes actin at (-) end Cap Z- Bind to and Stabilizes (+) end Formins- Assemble unbranched filaments Tropomodulin- binds to (-) end and prevents -Sit at (+) end, regulates growth, prevents Actin can also Branch disassembly -FH2 Domain dimer Cytochalasin-depolymerizes actin (Drug) -Has to be activated to work through Phalloidin- Stabilizes Actin (Drug) RhoGTPase bindingto actin, branch grows from Apr2/3 with (+) end growing away -Apr2/3 regulation; a nucleation promoting factor (
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