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LECTURE 3 - NONMUSCLE CELLS & CELL LOCOMOTION

LECTURE 3 - NONMUSCLE CELLS & CELL LOCOMOTION. Non-Contractile Bundles Lamellipodia Filopodia Surface Projections Non-Muscle Cells Circumferential belt Cortical attachment Stress fibers Cytokinesis Vesicle transport Cell Locomotion. Lamellipodium. Broad membrane protrusion

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LECTURE 3 - NONMUSCLE CELLS & CELL LOCOMOTION

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  1. LECTURE 3 - NONMUSCLE CELLS & CELL LOCOMOTION • Non-Contractile Bundles • Lamellipodia • Filopodia • Surface Projections • Non-Muscle Cells • Circumferential belt • Cortical attachment • Stress fibers • Cytokinesis • Vesicle transport • Cell Locomotion

  2. Lamellipodium • Broad membrane protrusion • Moves forward from cell • Forms focal adhesions • Fills with cytosol • Rear of cell retracts toward process

  3. Lamellipodium

  4. Filopodia • Finger-like extensions of memb. • Form focal adhesions on ventral surface • Form ruffles on dorsal surface

  5. Microvilli • Microvilli and filopodia – internal actin bundles • Actin linked by fimbrin, villin (intestine) and spectrin (RBCs)

  6. NON-MUSCLE CELLS - PROTEINS • Actin • Myosin type I • Assoc. w/ cell memb • Does not form thick filaments • Myosin type II • Forms prominent bundles w/ actin • Powers muscle contraction & cytokin • Myosin type V • Cytoskeletal-memb. interactions • Transport of memb. vesicles

  7. CONTRACTILE BUNDLES • Prominent bundles of actin & myosin II • Located at points of cell contact • Differ from non-contractile bundles • Myosin II interspersed with actin

  8. CONTRACTILE BUNDLES - EXAMPLES • Circumferential belt • Cortical attachment • Stress fibers • Cytokinesis • Vesicle transport

  9. Circumferential belt • Linker proteins to cell adhesions mol. in memb. • Forms junctional complex in epith. • Works like tension cable – wound heal

  10. Cortical Attachments • Network of actin • Attached by filamin • Strengthen memb. • Help w/ memb. transport • Myosin II acts as small tension rods

  11. Stress Fibers • Static bundles of actin • Form radial & axial bund. • Alternating patches of myosin & α-actinin • Contain • Tropomyosin • Caldesmon • Myosin LC kinase (SM) • Attach at focal adhesions

  12. Contractile ring Actin and myosin II accumulate at equator of dividing cell Cytokinesis

  13. Vesicle Transport • Actin & microtubule networks • Myosin I & V • Myosin carries cargo • Cytoplasmic streaming

  14. Vesicle Transport

  15. CELL LOCOMOTION SEQUENCE • Extension of cell membrane • Attachment to substratum • Forward flow of cytosol • Retraction of rear of cell

  16. Protrusion of Lamellipodium • Controlled polymerization of actin • Actin cross-linked • Memb. pushed forward by polymerization

  17. Focal Adhesions • Actin anchored to substratum • Develops into focal adhesion • Anchors cell to substratum • Prevents lamella from retracting

  18. Cell Body Movement • Unknown mechanism • Translocate bulk contents of cell • Contraction of stress fibers • De-adhesion of focal adhesions

  19. Gel-Sol Transformation • Transformation – disassembly and reassembly of actin network • Process controlled by actin binding prot. • Profilin – promotes polymerization (gel) • a-actin and filamin form gel-like network • Cofilin sever actin filaments (sol)

  20. Gel-Sol Transformation

  21. Myosins • Myosin I – leading edge – forward • Myosin II –trailing edge - retraction

  22. Polarity • Front and back polarity • Wound stimulates growth of processes • Stress fibers help close wound • Signal-transduction pathways control activation • Chemotactic mol. bind to cell-surface receptors and activate signaling • Ca2+ - high at leading, low at rear

  23. LOCOMOTION SUMMARY

  24. Dynamics SummaryAlberts et al, 1994

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