Cytoskeleton Flashcards
main function of the cytoskeleton
cell shape, cell wall formation, intracellular movement, cell metabolism
cytoskeleton is composes of what 2 parts mainly
microtubules and actin filaments
Microtubules
structure of MTs (3 main pieces)
tubulin dimers, 13 protofilaments, polarity
MTs are composed of 2 types tubulin dimers:
alpha-tubulin and beta-tubulin
Microtubules are formed by 13 protofilaments that form [blank]
a hollow tube
MTs exhibit polarity, at what end does growth occur
growth at the (+) end, it also has a (-) end
Are MTs dynamic?
Yes, constantly growing and shrinking, which makes them a bit unstable
How is the instability of MTs regulated
regulated by the GTP/GDP state of the tubulin dimers
MTs are approx how long
25nm tubes
actin filaments are approx how long
7nm, aka microfilaments
GTP bound beta tubulin’s form? straight or bent? assembly or dissasembly?
GTP bound beta tubulin is straight, assembly
GDP bound beta tubulin is straight or bent? assembly or dissasembly?
GDP beta tubulin is bent, dissasembly
MT Polymerization and Catastrophe
how does a MT grow
add GTP dimers at the (+) end
how does MT catastrohpe happen
loss of GTP cap due to hydrolysis leads to rapid breakdown
how does EBI (End Binding Protein) influence MT dynamics
- binds to (+) end to GTP cap
- stablize elongation, prevent catastrophe
- guides growth and speed
where does MT nucleation happen
nuclear envelope and pre-existing MTs
what does γ-Tubulin Ring Complex (γ-TuRC) do
acts as a template for forming new MTs, providin starting point and polarity for GTP cap to attach and begin elongation and polymerization
cell wall structure and formation
[blank] MTs guide the movement of [blank], which lays cellulose fibers in the cell wall.
cortical, cellulose synthase
MTs are crucial for organizing cellulose production, impacting cell wall [blank]
rigidity
Actin filaments are composed of [blank] monomers, which polymerize into [blank]
G-actin (globular), F-actin (filamentous)
Actin filaments are flexible and they can be strenghtened by [blank]. They do not form [blank] bonds
bundling, covalent
how does actin filament polymerization happen
ATP binds to G actin monomers, profilin plays a key role
how does profilin regulate polymerization in actin filaments
makes sure atp binds to g-actin at (+ end)
apart from prolifin, what else regulates polymerization
actin binding proteins regulate by promoting or repressing polymerization
two types of nucleation (formation) for actin filaments
formin-mediated, ARP 2-3 complex- mediated
formin mediated nucleation involves
unbranched, linear actin filaments, which recruits G-actin at the (+) end.
ARP 2-3 complex mediated nucleation involves
nucleation of branched AFs by growing (nucleating) off existing filaments, aiding in cell shape and motility.
function of AFs in plant cells
-vesicle delivery
-growth in pollen tubes
-found in cortical and transvacuolar strands of cytoplasm
what is treadmilling
MTs glide through the addition and loss of dimers at opposite ends, maintaining their structure while changing
Real-time observations reveal that MTs add or lose up to 20 dimers per second at the (+) end. What does this tell us?
allows for flexibility in cell structure
Actin filaments can form branches via the ARP 2/3 complex. Why is this important?
helps cells adapt shape to environment, especially in epidermal cells
Phalloidin, a toxin that binds to [blank]? What does it do?
F-actin, used to stain and visualize actin filaments
α-tubulin always binds [blank], while β-tubulin cycles between [blank]
GTP, GTP and GDP states
