Ctyoskeleton Flashcards
actin assembly
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
treadmilling
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
regulatory proteins of actin filament
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
filamin
crosslinks actin as it forms networks (similar to collagen IV)
fimbrin
holds actin filaments close together in parallel in forming actin bundles
alpha-actinin
holds actin filaments farther apart than fimbrin in actin bundles
Actin in cell migration
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
filopodia movement of actin filament
“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
Wiskott Aldrich Syndrome
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
myosin
moves stuff across the cell by binding a vesicle and then using actin filaments as a railroad system across the cell
3 cytoskeletal proteins
1) actin
2) intermediate filaments
3) microtubules
inc in size
intermediate filaments
medium sized cytoskeletal protein
cell specific, differ by cell
can assemble at both ends
assembly of IF
1) 2 polypeptides twist into a dimer
2) 2 dimers stack to form a tetramer, do not twist
microtubules
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)
microtubule polymerization
originate from a centrosome
alpha-tubulin and beta-tubulin leave from the -end
and are added to the +end
dynamic instability of microtubules
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)
organization of microtubules in nerve cell
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
kinesin
microtubule motor protein that carries vesicles away from - end (centrosome side) to + end
requires ATP
dynein
microtubule motor protein the carries vesicles from + end to - end
requires ATP
cilium axoneme
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
