Actin

Question 1

phalloidin

Answer 1

stabilizes F-actin; prevents depolarization

Question 2

structural roles for actin

Answer 2

microvilli in intestinal brush border, stereocilia in ear, scaffold for myosin

Question 3

neutrophil actin

Answer 3

front end of neutrophil is a mass of actin fibers that form and dissociate –> rapid formation drives movement towards bacteria

Question 4

issues for assembling actin

Answer 4

polymers composed of globular subunits are flexible but not strong, nucleation of a helical polymer is difficult

Question 5

nucleation of helical polymer solution

Answer 5

add a nucleator

Question 6

globular subunit solution

Answer 6

helical polymer is stabilized by multiple contacts

Question 7

Arp2/3 complex

Answer 7

nucleator for actin

Question 8

listeria monocytogenes

Answer 8

discovery led to understanding of actin polymerization; creates an actin tail to escape phagosome

Question 9

listeria mechanism

Answer 9

express ActA on one pole –> activates Arp2/3 complex –> initiates polymerization –> capping proteins terminate elongation branches –> cofilin cleaves actin filaments –> profilin exchanges ADP for ATP

Question 10

actin capping protein

Answer 10

bind to + end of actin filament and terminates elongation

Question 11

profilin

Answer 11

exchanges ADP for ATP to speed elongation

Question 12

cofilin

Answer 12

cleaves actin filaments by binding ADP actin filaments

Question 13

wiscott aldrich syndrome protein (WASP)

Answer 13

has a regulatory domain and catalytic domain

Question 14

WASP regulatory domain

Answer 14

binds PI that is expressed on neutrophil near bacteria which activates WASP in that area

Question 15

WASP catalytic domain

Answer 15

binds Arp2/3

Question 16

forward movement of a cell

Answer 16

coordination of Arp2/3 membrane protrusion, focal contacts with substrate, contraction of rear via myosin motor

Question 17

formin proteins

Answer 17

promote nucleation and elongation by binding to plus end, allowing actin addition but excluding capping proteins

Question 18

force generation

Answer 18

association with molecular motors (myosin on actin filaments)

Question 19

myosin II

Answer 19

ATP-dependent movement of myosin on actin filament

Question 20

non-muscle myosin II

Answer 20

smaller bipolar filaments, regulated by Pi; required for cell movement, shortens actin filaments to move tail forward, acts in cytokinesis of cell cleavage

Question 21

muscle myosin II

Answer 21

bound to actin 5% of time, low processivity, bundles with other motor heads

Question 22

myosin V

Answer 22

bound 90% of time, high processivity, works alone to transport vesicle cargo