Cytoskeletal Organization Flashcards
Polar cytoskeltal organization
- Polar microtubules can trasnport vesicles and proteins to different ends of the cell
- Polarized actin can define cell shape and behaviour
- Intermediate filaments also contribute to polarity
Dynamic
rearrangements in interphase crawling/migrating cell
Microtubules radiate from cell centre
Actin enriches at cell cortex
Dynamic rearrangements in mitosis
Microtubules form the mitotic spindle
Actin at cell cortex disassembles
Dynamic rearrangements in cytokinesis
Microtubules keep cell components separate
Actin forms the contractile ring
whcih proteins form the tubulin diners in micrtubules
alpha (-) and beta (+) tubulins
what do tubulins in microtubules do?
they can bind and hydrolyze GTP
They assemble head to tails to make polarized protofilaments
How many protofilaments associate to form a single microtubule?
13
How to the filaments grow or shrink
After tubulins have been in protofilament for a while, beta tubulin will cut GTP to GDP. |
Growing and shrinking only happens at the ends. If u have GTP bound heterodimers at the end - growing; if u have GDP bound heterodimers at the end - shrinking.
alpha is always bound to GTP
gamma tubulin
helps to nucleate microtubules at minus end (hence interacts with alpha)
plus ends grow away from nucleation site.
where is gamma tubulin found in animal cells
pericentriolar material
where is gamma tubulin found in plant cells
on other microtubules
kinesins
walk towards plus end of microtubules
dyneins
walk towards minus end of microtubules
what is simlar between both motor proteins
they can hold onto vesicles or organelles with their other domain and they use ATP hydrolysis for energy
Colour in Tilapia fish
Dark: kinesins and dyneins compete for pigment containing vecicles
light: kinesisn are inhibits, dyneins move vesiclees towards minus end near centrioles.
Polarity in actin filaments
One side N and C terminus
Other side nothing
how many monomers to make a single actin filament
usually two strands twisted together
what do actin filaments undergo
treadmilling
ARP2 annd ARP3 (Actin related protein(
very similar structure to actin monomers
they nucleate the minus end of actin filaments and protect them from depolymerization
The plus ends grow away from the ARP2/3 complex
How do ARP2 annd ARP3 help form a complex
they nucleate actin filaments on pre-exisiting filaments
whole network can undergo treadmilling,
proteins sever the minus ends to release them from ARP2/3
Proteins cap the plus ends to shape the netwrok
How do actin treadmilling and adhesions help crawl
the growing actin network pushes the cell leading edge forward
Actin and myosin contract to bring thr lagging edge forward
integrins
they have alpha and beta subunits - focal adhesions
integrin heterodimers directly bind extracellular matrix proteins and indirectly interact with actin filaments
myosins
many types
use ATP hydorlysis for energy
they can hold onto vesicles or organelles with their domain or myosins can help cells contract
how do actin and myosin generate contractile forces
- some myosins can walk towards plus end of actin filaments
- Actin and myosin woork together to generate force (e.g cell migration or muscle contraction)
What do Rho family GTPases influence
actin organization which affects cell shape, polarity and behaviour
Wht does overactuvation of Rho family members do
different actin organization patterns
rac activation
gives leading edge; actin network treadmilling
rho activation
actin - myosin contraction
cytoskeletal polarization when soerm enters egg
- actin filaments are organized by a gradient of rho gtp activity
- microtubules are organized by centromeres near where the sperm entered.
generates anterior and posterior ends
