L4 - Cytoskeleton Flashcards
cytoskeleton function
1) framework for cell
2) stability
3) shape change (spreading)
4) cell movement
3 types of polymers
1) actin filaments
2) microtubules
3) intermediate filaments
actin filament monomer
actin
actin filament size
smallest
microtubules monomer
heterodimer made of a + B subunits of tubulin
intermediate filaments
intermediate filament proteins
what is the nuclear lamina beneath the inner nuclear membrane made of?
intermediate filaments
what are some times of intermediate filament proteins?
1) keratin
2) vimentin
describe mechanical characteristic of intermediate filaments
flexible and rope-like
why are intermediate filaments so flexible
staggered long subunits
similarities between microtubules and actin filaments
1) single protofilament is thermally unstable
2) two ends polymerize at different rates
minus end speed
slow growing
plus end speed
fast growing
how are microtubules assembled?
GTP hydrolysis (GTP-tubulin dimers = fast growing, GDP-tubulin dimers = fast disassembly)
in microtubules, where does disassembly occur?
at plus end
how are actin filaments assembled?
ATP hydrolysis
what is the rate determining step for actin polymerization?
nucleation (3 actin monomers forming a trimer)
F-actin
actin filament
G-actin
oligomer (3 actin monomers coming together)
critical concentration
minimum concentration of monomers needed for the net addition
where is critical concentration higher?
- end
where is critical concentration lower?
+ end
treadmilling range
range where concentration of monomers between CcT and CcD
nucleation
where monomers come together and form an initial stable structure to act as “seed” for polymerization
lag phase
time taken for nucleation
growth phase
monomers added to exposed ends of growing filament -“ elongation
eqm phase
growth of polymer balanced with shrinkage
dynamic instability
microtubules - phenomenon where microtubules alternate between a period of slow growth and rapid disassembly at one side
actin cytoskeleton function
cell spreading/migration
ARP2/3 complex function
adds additional nucleation sites and catalyze the formation of a branched actin network to grow near a cell membrane (stays at - end)
formin
nucleates new filaments at + end to accelerate polymerization
profilin
binds to subunits and brings to growing chain to speed elongation
cofilin
binds and destabilizes disassembly
capZ
caps actin filament at + end and prevents growth (greatly increases the critical concentration). only can grow at minus end so much slower
tropomyosin
stabilizes actin filament
stress fibres actin configuration
contractile bundle (by a-actinin)
cell cortex actin configuration
gel-like network (by filamin A)
filopodium
tight parallel bundles (by fimbrin)
phalloidin
Drug that binds F-actin and stabilizes it (can have fluorescent tag)
cytochalasin
drug that caps actin filament plus end
swinholide
drug that severs actin filaments
latrunculin
drug that binds actin subunits and prevent polymerization
taxol
drug that binds and stabilizes microtubules
colchicine
drug that binds MT subunits and prevents polymerization
colcemid
drug that binds MT subunits and prevents polymerization
vinblastine
drug that binds MT subunits and prevents polymerization
vincristine
drug that binds MT subunits and prevents polymerization
nocodazole
drug that binds MT subunits and prevents polymerization
Rho GTPase
catalyze important cell shape
cell shapes catalyzed by Rho GTPase
1) filopodia (spike-like proj)
2) lamellipodia (sheet-like proj)
3) stress fibers (contractile actin bundles)
RhoA activation
stress fibers (contractile actin bundles) -> more integrin + focal adhesion
Cdc42 activation
filopodia (spike-like proj)
Rac1 activation
lamellipodia (sheet-like proj)
Rac-Rho antagonism
Rac promotes protrusion
Rho promotes contract (opposite so need to be coordinated)
how is RhoGTPase deactivation regulated?
GEFs
how is RhoGTPase activation regulated?
GAPs
what protein is needed for cell-matrix adhesion?
integrin, transmembrane receptors (actin and intermediate filaments)
how is integrin activated?
receives signal and catalyze conformation chain where it opens up and allows for strong ligand binding
focal adhesion
catalyzed by FAK (involve integrin, actin and actin-binding proteins)