Cytoskeleton Proteins Flashcards
What are the kinds of cytoskeleton filaments:
microtubules, actin filaments, intermediate filaments.
describe Intermediate filaments -
no polarity, strong, ropelike, hard to break, coiled coils form tetramers, doesn’t bind triphosphate.
What are the diseases linked to intermediate filaments?
Epidermolysis bullosa complex - failure to form filaments, can’t withstand stress resulting in cell rupture,
ALS - Accumulation of neurofilaments in the cell body and axons
Progeria - defects in nuclear lamins
describe microtubule structure -
hard to break, stiff and difficult to bend, polar, includes alpha and beta tubulins that form protofilaments.
How does nucleation of microtubules happen-
occurs at gamma tubulin ring complex in microtubule organizing center, complex associates with minus end.
How is the centrosome related to microtubules?
It functions as the MTOC in animal centers, contains pair of centrioles, which ensure centrosome duplication during cell division.
What affects microtubule stabilization?
MAP stabilizes them, resulting in less dynamic microtubules. Kinesin 13 (catastrophe factor) causes destabilization, resulting in more dynamic microtubules.
What do capping proteins do?
stabilize microtubules by binding to plus end.
What is dynamic instability? .
Change from growth to rapid shrinking caused by change in GTP binding. Rapid growth occurs with GTP cap and loss of cap causes catastrophe and shrinkage
What do TIP Proteins do?
Modulate growth and shrinkage, control microtubule positioning.
What are regulators of microtubule function?
kinesin 13 - enhances catastrophic disassembly at plus end,
katanin - severs microtubules
stathmin - binds subunits and prevents assembly
tips- remain associated with growing plus ends
can link them to other structures such as membranes, MAPs- stabilize microtubules.
What helps formation of microtubule bundles?
MAP2 and tau
Describe Actin Filaments:
two stranded helix, flexible and easy to bend, easy to break, polar with more dynamic plus end.
How does actin filament nucleation occur?
It happens at the cell cortex and involves Actin related proteins that associate with minus end, involved in lamellipodia formation at leading edge for movement.
Web like networks of actin filaments formed.
What does formin do?
Form dimer that recruits two actin monomers, associates with plus end.
What does profilin do?
binds to formin whiskers, can increase rate of actin elongation.
Binds actin to prevent association with minus end, can only add to plus end.
Addition of actin to plus end results in conformation change
and release of profilin
Describe treadmilling:
Plus end is more dynamic, minus end more likely to be shrinking, subunits at minus end are bound to GDP which causes instability, one end grows, one end shrinks.
What is critical concentration and how does it relate to subunit addition/loss?
Concentration of available actin monomers. If the concentration of actin at one side is greater than Cc, subunits are added. If concentration at one side is lower than Cc, subunits are lost.
The minus end has a higher Cc than the plus end, so subunits usually lost from this side and added to plus end, resulting in treadmilling.
Describe assembly/disassembly of subunits.
Occurs quickly as subunits are held noncovalently. They disassemble and assemble where needed due to easy diffusion of subunits.
Distinguish fimbrin, alpha actinin, filamin, spectrin, and ERM
fimbrin and a-actinin - form parallel structures
filamin - forms web like structures,
spectrin and ERM help actin associate with membrane.
What are stress fibers, cell cortex, and filopodium made of?
stress fiber - contractile bundle, cell cortex - gel like network, filopodium- tight parallel bundle
Describe web like structures:
Important for lamellipodia formation, filamin links actin filaments, loss of filamin in tumor cells makes them less invasive.
What is responsible for filament formation in actin and microtubules?
Actin: ARP 2/3, formin with profilin,
Microtubules: gamma tubulin ring complex (MTOC, centrosome)
What severs filaments in actin and microtubules?
Actin: Gelsolin
Microtubules: Katanin
