Talbot - cytoskeleton and actin filaments Flashcards
what is the dynamic instability of actin filaments
the filament is always growing and shrinking = “treadmilling” any given G-actin appears to move along a treadmill adding to plus end and falling off minus end
how is actin formed
ATP-actin binds to another ATP-actin - but it is unstable so if adds a 3rd ATP-actin = trimer/oligomer that serves as nucleus and induces formation
how does actin provide structural support and integrity of epithelial cells
as microvilli and as an “adhesion belt” of actin linking cytoskeleton to adjacent cells
where is actin used to sense vibrations
stereocilia in inner ear
why is dynamic instability important
for motility - rapid assembly and disassembly (migrated/crawl through environment)
how are actin filaments involved in cell division
contribute to miotic spindles and form contractile ring that helps pinch cell into daughter cells
how are actin filaments arranged in stress fibers
anti-parallel contractile bundles (help pull cell body towards front/leading edge)
how are actin filaments arranged in the cell cortex
loose, 3D gel-like network underlying the plasma membrane
how are actin filaments arranged in filopodiums (spike like projections of plasma membrane near leading edge)
tight, parallel bundles all orientated in same direction
what are monomer binding (sequestering) proteins
ex. thymosin - bind to G-actin and prevent them from adding to growing end; decrease concentration of free action monomers
what are nucleating proteins
ex. ARP 2/3 complex and profilin
they interact with the minus end to promote growth
what does ARP 2/3 do (nucleating/cross linking protein)
promotes networks: forms branch off existing filament and forms complex web
what are severing proteins
cut actin filament in middle exposing ADP-actin - promotes depolymerization and converts gel-like structures into liquid
what are cross-linking proteins
ex. filamin and ARP 2/3 complex
cross-link actin at angles to each other, web like structure
what are end-binding (capping) proteins
CapZ= specific for plus end
Tropomodulin = specific for minus end
prevent assembly and/or disassembly at capped off ends
what are stabilizing proteins
ex. tropomysin
helps stabilize filament and prevent depolymerization by competing with depolymerizing proteins like cofilin/ADF for binding sites
what are motor proteins
ex. myosin
walks along filaments
what are bundling proteins
help arrange actin filaments in stable/parallel structures
what do all types of myosin share
high degree of homology in N-terminus amino acid sequence, however C-terminus has variation
what is the myosin 1 subfamily
in all/most eukaryotic cells - monomeric myosin with single ATPase head and tail
which direction do myosins “walk”
towards the plus end of the actin filament
what is the myosin 2 subfamily
“muscle” myosins - 2 subunits interact to form structurally polar homodimer with tails forming coil
where are bi-polar thick myosin filaments located
in skeletal or cardiac muscle
why are bi-polar thick myosin filaments called bipolar
one end is exposed and other is oriented into center - N-terminus is found at either end and C-terminus is towards center
