actin

Question 1

what are actin filaments?

Answer 1

microfilaments - helical polymers of protein actin

Question 2

what are actin subunits?

Answer 2

called globular or G-actin
a polypeptide carry8ing ATP or ADP

Question 3

what does actin assembly provide?

Answer 3

polarity to the filament (- end = atp-binding pocket exposed, + end = atp-binding pocket is buried

Question 4

where does growth happen in actin?

Answer 4

in the + end mostly

Question 5

what purpose does nucleation have?

Answer 5

is it the rate-limiting step in formation of actin filaments

Question 6

what affect does numner of actin molecules bonding have?

Answer 6

two molecules are a weak bond, three is more stable

Question 7

what is phalloidin?

Answer 7

drug that stabalizes F-actin

Question 8

what are filopodia and lamellipodia?

Answer 8

protrusive structures made by migrating cells

Question 9

what do actin-binding proteins do?

Answer 9

regulate polymerization and length of filaments

Question 10

where do capping proteins bind?

Answer 10

to the + ends of actin

Question 11

what does cofilin do?

Answer 11

cuts actin filaments into small pieces

Question 12

what does actin crosslinking makes?

Answer 12

complex structures such as filopodia and lamellipodium

Question 13

what is alpha-actinin?

Answer 13

a crosslinking protein that makes F-actin bundles (a rigid dimer)

Question 14

what is filamin?

Answer 14

a flexible actin crosslinker protein (flexible dimer)

Question 15

what is the Arp2/3 complex?

Answer 15

made of 7 subunits similar to G-actin
promotes actin branching by binding to the side of ta filament and recruiting actin monomers

Question 16

what are ERM proteins?

Answer 16

link actin cytoskeleton to membrane
Erzin, Radizin, Moesin (ERM)

Question 17

what do cells change to assemble complex actin structures?

Answer 17

activity and localization of actin-binding proteins

Question 18

what are filopodia used for?

Answer 18

probe environment for clues in migrating cells

Question 19

what are Rho Rac and Cdc42?

Answer 19

small GTPases (signal formation of actin strucutres)

Question 20

what family are actin-based motor proteins?

Answer 20

myosin superfamily

Question 21

what do all mysosins share/differ?

Answer 21

similar motor domains
C-terminal tails are different (can be conventional or unconventional)

Question 22

what do myosin heads do?

Answer 22

bind and hydrolyze ATP to walk towards + end of actin

Question 23

what is myosin V?

Answer 23

two-headed molecule that that walks along actin to transport/disperse cargo

Question 24

what is mysoin 1?

Answer 24

one head, binds membranes

Question 25

what are the parts of myosin 1?

Answer 25

tail - binding (anionic phospholipid, protein cargo, phosphoinositide)
LCBD (arm) - regulates Ca, force, binds CaM chains
motor - forge and ATP generation, regulated by tropomyosin

Question 26

what are myosin 1 mutants?

Answer 26

left/right inverted

Question 27

what does myosin II do?

Answer 27

forms bipolar filaments

Question 28

what do myosin light chains do?

Answer 28

they are regulatory subunits of myosin II

Question 29

what does MLCK do?

Answer 29

phosphorylates the myosin light chains and unfolds myosin II into active state

Question 30

what are stress fibers?

Answer 30

contractile actin bundles found in non-muscle cells (composed of actin filaments and non-muslce myosin II)

Question 31

what is a myosin power stroke?

Answer 31

ATP binds to myosin head -> release of actin -> conformation shift in lever arm -> actin releases phosphate (power stroke generates force) ->myosin head and actin bound