Lect 06 F10 - M i cr ofi l a ments a nd Cel l Locomoti on...

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Barbara Danowski. Nikon Small world winner (1997). Stress fibers in mouse fibroblasts Microfilaments and Cell Locomotion
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A) Microvilli (increases absorption surface area in intestinal epithelial cells) B) Stress fibers (adhesion to substrate) C) Lamellipodia and filopodia (cell locomotion) D) Contractile ring (pinches cells in two during mitosis) E) Contractile apparatus of muscle cells Microfilaments are typically found underneath the plasma membrane (cortex). They can extend the membrane or cause it to contract.
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nucleating protein (and proteins that regulate nucleating activity) severing protein (gelsolin) cross-linking protein in cell cortex (filamen, spectrin) side-binding protein (tropomyosin, cofilin) bundling protein (fimbrin, α -actinin) monomer-sequestering protein (thymosin, profilin) Inside the cell, the assembly and organization of microfilaments is controlled by a large group of actin binding proteins motor protein (myosin) actin monomers actin filaments + + (Arp2/3 complex) capping /end-blocking protein (CapZ)
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The ARP complex can nucleate actin assembly The ARP complex can bind to sides of preexisting actin filaments! -analogous to γ -TuRC nucleation of microtubules
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Microfilament assembly is regulated by actin monomer binding proteins Actin monomer concentration is high in most vertebrate cells (50-200uM). Thymosin binding ‘locks’ monomer in assembly incompetent state.
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Lect 06 F10 - M i cr ofi l a ments a nd Cel l Locomoti on...

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