Cytoskeleton: Intermediate filaments, cell motility Flashcards

Question

Describe how bundles of actin filaments and myosin 2 filaments formed in non muscle cells

Answer 1

Formed transiently to perform specific functions and then disassemble = dynamic system

Answer 2

Relatively abundant in cortex of non muscle cells Stress fibres are prominent in cultured fibroblasts = Represent a temporary contractile bundle of actin filaments and myosin 2

Answer 3

Transient increases in calcium - binds calmodulin = activates myosin light chain kinase = mlck

Answer 4

Mlck phsophorylates 2 light chains associated with Myosin head = has 2 effects

Answer 5

Release of myosin 2 from a binding site on the head, allows myosin 2 to form bipolar filaments = heads open up Change in conformation of myosin head exposing acting binding site =allows interactions between actin filament and myosin 2 filaments = leads to contractile response

Answer 6

Involved rho gtpase Active rho (rhogtp) = activates rho kinase = promotes activation of mlck Rho kinase all phosphorylates and inactivates mlck phosphatases (remove phsophate) = prevents dephosphorylation and inactivation of mlck = exposes head and allows tails to do coiled coil conformation

Answer 7

In skeletal muscle = actin myosin interacted regulated by actin based regulatory system Calcium binds troponin = moves tropomyosin, myosin ready but tropomyosin in way Tropomyosin binds in groove of actin filament helix and blocks binding site of myosin head = myosin head can interact when tropomyosin gone

Answer 8

Protrusion Adhesion Traction Deadhesion/tail retraction

Answer 9

Actin polymerization Involves forward of the membrane at the front of the cell - at Leading edge of cell

Answer 10

Integrins Required for protrusion to be translated to movement along a surface

Answer 11

Myosin 2 Process leading to forward movement of nucleus and cell body Also sometimes myosin 1

Answer 12

Myosin 2 Mehcanistically distinct processes involved in last step of cell locomotion Some cells do leave parts behind tho

Answer 13

Actin cytoskeleton rapidly moving cells can move without microtubuels - like keratinocytes, neutrophils but crawling motility always needs actin (Myosin related process = retraction, external signals = bind cortex and mt gets signal = knows where to go, gradient based, retrograde g actin comes back to feed cell, coil in breaks up actin behind polymerizing actin )

Answer 14

Microtubules = steering wheel Actin polymerization = engine = generate force

Answer 15

Spatial asymmetry to migrate = need clear distinction between front and back of cell Marked by increase in concentration of actin filaments at a particular region of cell

Answer 16

2 types of protrusion structures can be discerned at front of migrating cell = filapodia and lamellapodia

Answer 17

Cdc42 Thin, cylindrical projections, contain actin filaments organized into tight bundles which exclude myosin’s

Answer 18

Rac Broad, flat, sheet lie in which actin filaments are more loosely organized in orthogonal criss crossed pattern due to actin filament cross linking protein and arp2/3 complex Senses environment and leads to leading edge

Answer 19

Have barbed + end of actin pointing at leading edge Accepted model = generated by actin polymeriztaion alone Af cross linkers import bc increase rigidity of actin bundles or networks to facilitate pushing forward on membrane Each monomer on to filament pushes membrane further *70degrees -arp2/3

Answer 20

Cell signal - like chemoattractant binding to receptor - at membrane = activates wasp Wasp = activates arp2/3= initiates f actin polymerization Arp2/3 binds to walls of f actin = initiates branching f actin - at 70 degrees F actin grows at barbed end and depolymerizes at pointed end = causes pm to push out - leading edge

Answer 21

Pathogenic bacteria = listeria monocyogenes, gram + , can cause life threatening illness = encephalitis Listeria can invade mammalian cells and once internalized = bacterium escapes membrane bound endosomes and replicates and resides happily within cytoplasm of host cell Force pushing bacteria Within cell = bacterua hijacks host machinery required for actin polymerization and generates actin comet tail = propels bacterium within host cell Bacterial motility directly coupled to actin polymeriztaion - independent of myosin function -actin formed by arp2/3 bacterial version

Answer 22

Required to stabilize and consolidate forwards protrusive movements Experiments have shown that front of cell = preferential locus where adhesions from Newly synthesized and cycled integrins transported to leading edge of new cell bc leading edge constantly losing adhesion receptors - as cell moves forwards Inetgrins - binds surface then actin and myosin pull in that direction Integrins recyeld = endocytosed often bc only limited number of them

Answer 23

Also need contractile force to move cell forward Contractile force must overcome resistance in order to effective translocate the cell body - resistance due to adhesive interactions of Integrins and breaking these interactions -requires application of physical stress via contraction of myosin 2 and af MYOSIN 2 BASED Pulling of cell body forwards by contractile forces acting between back edges of leading lamella and nucleus could also involve myosin 1

Answer 24

Rapid cell migration requires efficient mechanism to release adhesion at rear of cell Mechanism for deadhesion seen in fibroblasts = involves membrane ripping = Integrins left behind on substratum as cell moves forward, Integrins remain on cell surface and are endocytosed into vesicles and reused at leading edge - ripping which leads to tail retraction = myosin 2 mediated process