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Cilia and FlagellaoUse core of microtubules from basal body- generate the axonemeCilium beats by performing repetitive rounds of a “power stroke”Actin filamentsoActin filaments are thin and flexibleoMany proteins bind to actin and modify its propertiesoAn actin rich cortex underlies the plasma membrane of most eukaryotic cells cell crawling depends on actinoActin associates with myosin to form contractile structuresoIMPORTANT- extracellular signals control arrangement of actin filaments allowing cell to respond to environmento5% total protein in a typical animal cell is actino½ of actin is assembled into filaments, and other in actin monomer in cytosolActin filaments allow cells to adopt a variety of shapesoActin fibers like microtubules are unstableoMade stable by interactions with other proteins “actin binding proteins”oDifferential interactions determine “stiffness” of structureoCan for stuff microvilli or flexible cellular musclesoCan create temporary protrusions or a contractile ring which pinches offActin binding proteins control behavior of actin filaments in vertebrate cells- formins andactin related proteins (ARP’s) control actin assemblyThe cortex- actin rich network under cytoplasm, and gives cell its shape and allows it to moveCell movementoCell first pushes out protrusions at its front or leading edgeoThe protrusion adheres to surface over which cell is crawling
oThe rest of the cell drags itself forwardCell crawling relies on actinoIntegrins- transmembrane proteins which bind to extra cellular matrixA web of actin filaments pushes the leading edge forwardActin associates with myosin motor proteins to form contractile structuresoCarry vesicle along actin filament tracksoBind plasma membrane and move relative to cortical actin = change shapeExtracellular signals control the arrangement of actin filaments- allows the cell to respond to its environmentsHow do cells contract?oMuscle contraction depends on bundles of actin and myosinoDuring muscle contraction, actin filaments slide against myosin filamentsoMuscle contraction is triggered by a sudden rise in Ca2+oMuscle cells perform highly specialized functions in the bodyMyosin II molecules can associate to form myosin filamentsoTails associate to form bipolar myosin filament- heads project outward from the middle in opposite directions; globular heads- bind ATPActin filaments slide along myosin filamentsoSlide actin filaments over each other = shortening of actin bundleoThe myosin head walks towards the actin plus end of the actin, causing contractionSkeletal muscle is packed with myofibrilsoIn skeletal muscles, cells fuse to form long fibers, the cytoplasms contain myofibrilsoMyofibrils- contractile elements of the muscle celloSarcomeres- contractile units of the myofibrils
Sacromeres are the contractile unit of the muscleoStacks of actin and myosin filamentsoContraction of a muscle is due to simultaneous shortening of all the sarcomereso2 types- thin and thick. Thick filament (myosin)- centrally located; thin filament