Final: Ch 17 Actin Filament Assembly, Cell Structures

Question 1

the rate-limiting step of actin polymerization is what

Answer 1

formation of the actin nucleus that a filament grows from

used as a regulation point

Question 2

2 major classes of actin nucleating proteins are

Answer 2

the formin protein family, and the Arp 2/3 complex

controlled by signal transduction pathways

Question 3

formins lead to the assembly of _____ actin filaments, whereas the Arp2/3 complex leads to _______ networks

Answer 3

long, branched

Question 4

2 important domains of formins

Answer 4

FH1 and FH2 domains

bind actin subunits (FH2) and block CAP protein

increase concentration of profilin-ATP-G-actin complexes (FH1)

Question 5

how is formin regulated

Answer 5

membrane bound Rho-GTPase

when it is switched from Rho-GDP –> Rho-GTP, it binds and activates formin

Question 6

formins assemble long actin filaments like….

Answer 6

stress fibers

filopodia

contractile ring

Question 7

Arp2/3 interacts with what to become a nucleator

Answer 7

nucleation promoting factor (NPF)

allows Arp2 and Arp3 to change into the correct conformation

binds branch at 70 degrees to side of actin filament

Question 8

intracellular movements can be powered by _____ __________

Answer 8

actin polymerization

b/c ATP hydrolysis

Question 9

intracellular bacterial parasite Listeria monocytogenes

Answer 9

food-borne parasite that causes mild GI problems

to move from one host cell to another it polymerizes actin into a comet tail

when it reaches the membrane, it pushes itself inside

Question 10

how does Listeria polymerize actin

Answer 10

has a surface protein called ActA that mimics a NPF to activate Arp2/3

Question 11

actin assembly powers what type of endocytosis

Answer 11

fluid-phase

Question 12

endocytosis assembly factors recruit __s so as the endocytic vesicles invaginate, they are propelled into the cytoplasm

Answer 12

NFPs

causes a short-burst of actin polymerization using the Arp2/3 complex

Question 13

phagocytosis

Answer 13

WBC engulf pathogens

uses microfilaments and myosin motor proteins to draw the pathogen into the cell

Question 14

fungi and sponges have toxins that target the polymerization cycle of actin…one class increases the monomer pool

Answer 14

cytochalasin D - depolymerizes actin by binding + end and blocking addition of monomers

latrunculin - binds G-actin to prevent its addition

Question 15

class of toxins that shifts the monomer-polymer equilibrium in favor of filaments

Answer 15

jasplakinolide - stabilizes actin dimers

phalloidin - prevents F-actin only from depolymerization

Question 16

____-____ proteins organize actin filaments into bundles or networks

Answer 16

cross-linking proteins

Question 17

to be able to organize actin, an actin cross-linking protein must have two…

Answer 17

F-actin binding sites

Question 18

fimbrin

Answer 18

a cross-linking protein w/ 2 actin binding sites found in microvilli that builds bundles of actin filaments with the same polarity

found in microvilli, filopodia, focal adhesions

Question 19

a dimeric cross-linking protein has what

Answer 19

1 actin binding site

2 chains associated into dimers that bring 2 actin binding sites together

Question 20

alpha-actinin

Answer 20

a dimeric cross-linking protein that forms a rigid rod connecting two binding sites

found in stress fibers, filopodia, muscle Z lines

Question 21

spectrin

Answer 21

cross-linking protein found in the cell cortex of RBC

makes networks under the plasma membrane to hold cell together during transport

anemia if mutation (low O2 delivery)

Question 22

filamin

Answer 22

cross-linking protein with a flexible region that makes stabilizing cross-links between filaments in a mesh

found in the leading edge, stress fibers, filopodia

Question 23

the Arp2/3 complex is also an important _____-_____ protein

Answer 23

cross-linking protein

binds the - end of one filament to the side of another filament

Question 24

_____ proteins link actin filaments to membranes

Answer 24

adaptor proteins

ex. in RBC

Question 25

how do RBC survive pumping by the heart, flowing through arteries, and squeezing through capillaries

Answer 25

a microfilament based network with tensile strength and flexibility

based on short actin filaments stabilized on their sides by tropomyosin and the capping protein tropomodulin (-) end

Question 26

mutations in which proteins cause anemia in humans

Answer 26

spectrin

band 4.1

ankyrin

Question 27

what is the orientation of actin filaments in microvilli

Answer 27

+ end at the tip

Question 28

adherens junctions

Answer 28

specialized regions of the plasma membrane where epithelial cells contact each other

Question 29

focal adhesions

Answer 29

specialized regions that mediate attachment of cells to the ECM

Question 30

dystrophin

Answer 30

a protein that links the cortical actin network of muscle cells to the ECM

absence causes muscular dystrophy

Question 31

what is the purpose of cross-linking actin filaments

Answer 31

structural support - holds cell together