2.2: Cytoskeletal Networks Flashcards
polarized cells can: (3)
- define inside vs outside
- have different functions at different cell regions
- transmit signals
what can polar microtubules do?
transport vesicle and proteins to different ends of the cell
what can polarized actin do
define cell shape and behaviour
intermediate filaments can also contribute to cell _________
polarity
the cytoskeleton undergoes __________ rearrangements
dynamic
describe how microtubules and actin contribute to interphase crawling/migrating cell, mitosis, cytokinesis
- interphase crawling/migrating cell: microtubules radiate from cell centre, actin enriched at cell cortex
- mitosis: microtubules form mitotic spindles, actin at cell cortex disassembles
- cytokinesis: microtubules keep cell components separate, actin forms the contractile
== main point is that you can rearrange the cytoskeleton
which monomeric proteins form tubulin dimers
alpha (-) and beta (+) tubulin
tubulins can bind and hydrolyze ____
gtp
tubulin heterodimers assemble head to tail to make what
polarized protofilaments
___ protofilaments associate to form a hollow ____________
13, microtubule
what conditions lead to faster depolymerization
100x faster at an exposed d form heterodimer
describe the growth of microtubules
- microtubules undergo dynamic instability.
- after they’ve been in the protofilament for awhile, b tubulin will cut the gtp to gdp (a tubulin always gtp)
- growing and shrinking only happens at the end - if you have gtp bound heterodimers at the end you’re more likely to have growth (gtp cap)
- if there is random loss of the gtp cap it’ll lead to rapid shrinkage
which form of tubulin helps to nucleates/stabilizes microtubules and which tubulin does it interact w
γ-tubulin, interact w a-tubulin at the minus end
what does γ-tubulin protect microtubules from at the - end
depolymerization
____-ends in microtubules grow away from the nucleation site
plus-ends (b)
in animal cells, where is γ-tubulin found nearby and state other features of this
γ-tubulin is found NEAR centrioles, there is a pair of them in the centrosome. γ-tubulin ring complexes (nucleating sites) are on the pericentriolar material (γ-tubulin attaches to accessory proteins in the γ-tubulin ring complex ie augmin) - this is what nucleates/stabilizes the - end.
γ-tubulin can only be found on other microtubules
γ-tubulin can be found on other microtubules leading to branches, what protein joins the γ-tubulin to the other microtubule
augmin
explain how vesicles and organelles can be transported along microtubules
- maps = microtubule associated proteins
- some kinesins can walk towards + end
- some dyneins can move towards the - end
- both motors can hold onto vesicles or organelles with their other domain
- both motors use atp hydrolysis for energy
contrast how fish eg tilapia can change color using microtubule motors
- dark fish: kinesins and dyneins compete for pigment-containing vesicles (melanosomes)
- light fish: kinesins are inhibited, vesicles are moved to minus ends near centrioles due to dyneins
Which of these statements about microtubules is true?
a) When a centrosome is present, each microtubule contains a variable number of protofilaments.
b) Long, growing microtubules will contain GTP and GDP.
c) A cell with many microtubules will not have any actin filaments.
d) ɣ-tubulin stabilizes microtubule minus ends by anchoring them onto a cylindrical centriole core
b.
a is wrong bc it doesn’t matter if centrosome is present. c is wrong bc it’s not mutually exclusive. d is wrong bc it’s not on the centrioles, its on γ-tubulin ring complexes.
actin monomers can bind and hydrolyze atp/gtp
atp
polar actin monomers assemble into polarized actin filaments, usually ___ strands twisted
2
for actin filaments, which conditions is depolymerization much faster
at an exposed d form monomer
soluble actin subunits are in t/d form, polymers are/are not a mix of t form and d form
soluble actin subunits are in t form, polymers are a mix of t form and d form
in actin filaments, - end addition is _____ (hydrolysis catches up), + end addition is _____ (hydrolysis lags behind)
slow, fast
*this happens at the right [C]
the ARP2/3 complex helps to __________ actin filaments
nucleate/stabilize
explain how the the ARP2/3 complex helps to nucleate/stabilize actin filaments
- arp2 and arp3 have very similar structure to actin monomers
- the arp2/3 complex nucleates the - end of actin filaments and protexts them from depolymerization
- ends group away from the arp2/3 complex
- the inactive arp2/3 complex becomes activated with a nucleation-promoting factor (npf)
- arp2/3 can nucleate actin filaments on pre-existing filaments; the whole network can undergo treadmilling
- proteins eg cofillin sever the - ends to release them from arp2/3 complex
proteins cap the + ends to shape the network (you want + ends to go towards membrane
in actin, which direction do you want + ends to be
to the membrane
what do proteins such as coffilin do
they sever the - ends of actin to release them from arp2/3 complex
describe how nucleation promoting factors (npfs) can help the cell move
- npfs look like hooks and they are on the inside side of the cell - membrane
- npf nucleates more actin filaments = elongate + ends = poking cell membrane = pushes it forward
explain the concept of leading and lagging edge in actin treadmilling
- the growing actin network pushes the cell leading edge (lamellipodium) forward
- actin and myosin contract to bring the lagging edge forward
_________ ________ directly bind to ecm proteins to INDIRECTLY interact w actin filaments
integrin heterodimers
_______________ interactions can provide the adhesion necessary for cell migration
actin-integrin-ecm interactions
is the interaction between integrins (eg adaptor/anchor prots) and actins indirect or direct
indirect
what are focal adhesions used for in actin
focal adhesions which are formed by integrins are tm proteins which helps the actin grip the substratum/floor
myosins motor domains use ____ hydrolysis for energy
atp
what are some functions are myosins
- there are many types of myosins
- they can hold onto vesciles or organelles with their other domain or myosins can help cells contract
- some myosins can “walk” towards the + end of actin filaments, acitn and myosin work tgt to generate force (eg cell migration or muscle contraction)
A graduate student adds actin monomers and ATP into a test tube with a
buffer that resembles the cell cytosol. What else must be added to the tube
to produce ADP?
a) Severing protein cofilin.
b) Nucleating protein ARP2/3.
c) Cofilin and ARP2/3.
d) Nothing.
d.
recall that actin binds to atp and assembles into the protofilaments. actin will cut the atp to the adp and actin will also eventually catalyze the cleavage.
cofilin cuts actin filamnets and atp2/3 nucleates actin filaments
rho family small gtpases can influence _______ organization
actin
rho, rac, and cdc42 are all examples of what, and can influence actin organization (which affects cell shape, polarity, and behaviour)
rho small family gtpases
rho family gtpases can act like what
molecular switches
t/f healthy cells have a balance of actin rho family members (rho, rac, and cdc42)
true
describe the actin organization patterns if different rho family members are over activated
★ rho: dominates at the back to pull the back of the cell. there is lots of rho def and gap = see lots of actin and myosin fibers contracting and is everywhere instead of just the lagging edge
★ rac: dominates at the leading tip/edge to explore and push the cell forward (polymerization/protrusion) = all over the cell now
cdc42: rearranges actin
in neutrophils, which rho small family member will be activated when lots of chemoattractants on a receptor
rac, most receptor activation=most rac bc it wants to go there
local cytoskeletal organization can define cell ___________
movements
symmetry breaking defines _________ vs _________
anterior (face) vs posterior (butt)
describe how cytoskeletal polarization works in c.elegans
in c. elegans, sperm entry defines the posterior. this triggers cytoskeleton polarization in the fertilized egg - actin filaments are organized by a gradient of rho-gtp activity (rho gef gradient), microtubules are organized by centrosomes near where the sperm entered.
Which of the following would most directly increase the amount of
constitutive protein secretion?
a) A chemical that increases the formation of COPI-coated vesicles.
b) A chemical that increases the formation of COPII-coated vesicles.
c) A chemical that increases the formation of clathrin-coated vesicles.
d) A chemical that increases the activation of ESCRT-0.
b
