Cytoskeleton Flashcards
list the proteins of cytoskeleton from dynamic to least dynamic
Actin –> microtubules –> intermediate filaments
intermediate filament is the place that
the place that cell terminates
stronger, so resistant to mechanical stress
fuses tight spot wells in desmosomes
actin
necessary for locomotion, secretion, endocytosis
movement of cell
microtubules
determines position of organelles and direct intracellular/cargo transport
tracks for protein transport
tubulin,
protofilaments bundle together to
create more stable structure
filament with place it terminates:
intermediate filament
attached to desmosomes
hemidesmosomes
microvilli are which filament
actin
which filament uses a dimer
microtubules (tubuilin)
which filament uses a monomer?
actin
stable cell surface protrusion is formed by which filaments?
actin
via microvillus
polymerization
assembly of actin/tubulin submits into polymer
require active form (T-from)
T form– ATP bound D form- ADP bound
depolymerization
removal of monomer at ends of polymer
nucleation
vital step in cytoskeletal construction
movement of protofilaments to nucleus/aggregation of filament
what is the rate limiting step in cytoskeletal construction?
nucleation
treadmilling is associated with which filament?
actin
elongation
quick addition the ends of nucleated filaments
growth pahse
treadmilling
actin filaments
growth at the plus end of actin, shrinking at minus end
maintains constant length
dynamic instability is associated with which filament
tubulin of microtubules
aka catastrophe
occurs when the filament shrinks faster than addition of new
loss of cap and microtubule shrinks
what rescues catastrophe?
GTP subunits added at shrinking end and cap reforms
tubulin
heterodimer of alpha and beta tubulin
makes up microtubules
actin
monomer with binding sites for ATP
polarity of filaments
two distinct and dynamic ends
Plus and minus
plus end
fast growing/shrinking end
subunit addition occurs here
found in t form (active)
minus end
slow growing, pointed end
subunits are removed
found in d form (inactive)
steps in intermediate filament construction
NO nucleotide binding site and no polarity
monomer forms coiled dimer with another monomer = dimer
dimer finds another dimer, combines in antiparallel to ge tetramer
tetramer finds another tetramer to get 8 parallel tetramerrs
subunits of actin
formin
thymosin
profilin
ARP complex
formin
nucleates assembly of actin
remains associated with growing plus end
thymosin
binds to actin subunits
PREVENTS assembly
profillin
binds to subunits of actin
SPEEDS elongation/assembly
ARP complex (simple)
nucleates actin, assembly to form a web
remains associated with minus end
actin filaments
coffin
gelsolin
capping protein
tropomyosin
cofilin
binds ADP actin filaments
accelerates disassembly of actin
gesolin
severs actin filaments and binds to plus end
capping protein
prevents assembly and disassembly at plus end
tropomyosin
stabilizes filament
actin filament accessory proteins that function in bundling, cross linking, attachment to membranes
fimbrin, alpha actinin, filamin, spectrin, ERM family
monomer of an intermediate filament is…
an intermediate filament
monomer of an actin filament is…
G-actin
monomer of microtubules
a- and b-tubules
Tubulin dimers
staminin
y-TuRC
TIPS
staminin
binds subunits, prevents assembly
y-TuRC (general)
nucleates assembly and remains associated with minus end
TIPS
plus end tracking proteins
remain associated with growing plus ends, can link them to other structures
filament cross-linking
tau and map 2
plectin
tau and map 2
cause binding of microtubules
plectin
cross linking proteins
links microtubule to intermediate filament
kinesin 13
enhances catastrophic disassembly at plus end
Katanin
severs microtubules
MAPS
stabilizes tubules by binding to sides
XMAP215
microtubule association protein
stabilizes plus ends
accelerates assembly
formation of the webs (actin)
ARP
which part of the actin does ARP nucleate?
minus end, so growth is at plus end
if proper activating factor, monomers can skip rate limiting step of nucleation
ARP works best when…
bound to side of preexisting filament
cross linked
forming nucleate best what type…
unbranched
forming works at which end
plus
what keeps actin monomers soluble
in locked state
thymosin
what does thymosin compete with?
profilin
recruits them there
binds to actin, recruits more monomer and leaves due to conformational change
stabilization of the actin is done by
tropomyosin
keeps it from binding with other filaments
can also protect from cofilin
disassembly of actin is controlled by
coffin
binds to ADP actin filaments
finds older one
alpha actinin v. fimbrin
a-actinin cross links into LOOSE bundles, myosin II
fimbrin cross links into TIGHT bundles, no myosin II
they exclude each other
what stabilizes tubulin agains disassembly?
MAPs
MAP v. Tau
map has LONG projecting domain
tau has SHORT
3 activities of crawling (moving)
- polarization and protrusion (actin structures pushed to front)
- adhesion and traction (adhere to ECM and create traction sites)
- retraction (disassembly of adhesion)
3 protrusions in plasma membrane
filopodia
lamellipodia
pseudopodia
filopodia
1 dimensional
fibroblasts
microspikes
core of long bundled actin filaments
lamellipodia
epithelial cells, fibroblasts, neurons
2D, sheet
cross linked actin
unidirectional tread milling
pesudoposida
amoeba and neutrophils
3D projections filled with gel
what controls movement of actin?
chemotaxis
presence of peptides
Rho GTP Ases
molecular switch to control cell process
cycles between active GTP and inactive GDP
steps of chemotaxis
- GPCR activates PIP3
- PIP3 activates Rac and Rho
- Rac goes to front, activates ARP and lamellipodia protrusion
- G12/13 stimulates Rho simultaneously
- Rho works at back
