Ctyoskeleton

Question 1

actin assembly

Answer 1

1) formin initiates formation (rate limiting step)
2) G (globular) actin-ATP add together to make dimer, the trimers, then chain of F (filamentous) actin
3) keep adding G actin-ATP to plus(+) end = elongation
4) branching initiated by Arp2/3

Question 2

treadmilling

Answer 2

actin can be in steady state- G actin-ATP are added to + end, at same rate G actin -ADP are removed from - end

plus end -> barbed end; minus end -> pointed end

Question 3

regulatory proteins of actin filament

Answer 3

formin-initiates assembly of actin filaments and usually stays there
Arp2/3-starts branching
cofilin-clips and dissociates G actin monomers from F actin chain
profilin- replaces ADP w/ ATP on G actin
CapZ-binds + end to prevent degradation
tropomodulin-binds - end to prevent degradation

Question 4

filamin

Answer 4

crosslinks actin as it forms networks (similar to collagen IV)

Question 5

fimbrin

Answer 5

holds actin filaments close together in parallel in forming actin bundles

Question 6

alpha-actinin

Answer 6

holds actin filaments farther apart than fimbrin in actin bundles

Question 7

Actin in cell migration

Answer 7

when a cell migrates is sends a leading edge, attached, and then retracts/pulls the rest of the cell up with it
actin must move with and support the cell
filopodia-actin filament goes out to farthest extensions to lead
lamellipodia-actin bundles follow

Question 8

filopodia movement of actin filament

Answer 8

“Leading”

in order for actin filament to move towards the edge of the cell membrane, cofilin must remove G actin-ADP from -end, then twinfilin attaches to the G actin monomer, then profilin attaches and kicks off twinfilin and replaces ADP w/ ATP, then G actin-ATP is taken to +end where WASP/Scar (activates Arp2/3) and barbed end tracking protein add to F actin

Question 9

Wiskott Aldrich Syndrome

Answer 9

X-linked immune disorder that creates a defect in the WASP/Scar protein that allows F actin to from branches to make filopodia for cell movement
babies w/ wiskott aldrich bleed because their platelets/actin cytoskeleton don’t work right and they get a lot of infections because their immune system doesn’t work right

Question 10

myosin

Answer 10

moves stuff across the cell by binding a vesicle and then using actin filaments as a railroad system across the cell

Question 11

3 cytoskeletal proteins

Answer 11

1) actin
2) intermediate filaments
3) microtubules
inc in size

Question 12

intermediate filaments

Answer 12

medium sized cytoskeletal protein
cell specific, differ by cell
can assemble at both ends

Question 13

assembly of IF

Answer 13

1) 2 polypeptides twist into a dimer

2) 2 dimers stack to form a tetramer, do not twist

Question 14

microtubules

Answer 14

largest cytoskeletal protein
13 protofilaments of alpha-tubulin and beta-tubulin formed around a hollow center cylinder
inherently unstable
cell shape, cell locomotion, transport w/in a cell, important in cell division (pulls apart chromatid)

Question 15

microtubule polymerization

Answer 15

originate from a centrosome
alpha-tubulin and beta-tubulin leave from the -end
and are added to the +end

Question 16

dynamic instability of microtubules

Answer 16

in a cell, a cap tends to cover the -end of microtubules, preventing them from leaving there
the microtubules rapidly grows and shrinks from the +end depending on the amount/rate of phosphorylation of tubulin monomers

growth->more alpha or beta tubulin-ATP is being added than what is being hydrolyzed to tubulin-ADP
shrinkage/catastrophe->hydrolysis of ATP to ADP happens faster than alpha or beta tubulin-ATP is added

CLASP stops disassembly and rescues the microtubule by restarting assembly (ADP->ATP)

Question 17

organization of microtubules in nerve cell

Answer 17

In axon: +end always away from cell body, and -end always towards cell body
In dendrite: + and - ends can go both ways

there are binding proteins attached to the microtubules for stabilization:
On microtubules in axon->tau
On microtubules in dendrite->MAP2

MAP2 also acts to connect microtubules to IFs

in Alzheimer’s tau is not properly degraded and clumps

Question 18

kinesin

Answer 18

microtubule motor protein that carries vesicles away from - end (centrosome side) to + end
requires ATP

Question 19

dynein

Answer 19

microtubule motor protein the carries vesicles from + end to - end
requires ATP

Question 20

cilium axoneme

Answer 20

most prominent structural component of cilium (also flagellum)
9:2–> 9 microtubule doublets around a ring for movement, and an additional pair of fully formed microtubules in the center for stability and support
9 pairs are made of an A tubule that is fully former, and a B tubule that is not fully formed and attached to the A tubule
nexin-protein that makes sure A and B tubules stay together
basal body-where cilia grow from, are anchored from (9-2 start here)
9 pairs of microtubules make the cilia/flagella move by dynein walking towards the basal body, as one “foot” is one the A tubule of one doublet and the other foot is on the B tubule of the adjacent doublet

smoking clogs cilia in respiratory passages