6 – contraction & chemotaxis Flashcards
STRESS FIBERS =
actin bundles that contract & produce force
-Can shorten & produce force
(what pulls back foot of cell forward)
-Pulls back foot of cell forward
Fomins
Polymerize linear actin filament arrays
-(FH2 domains-on the end of actin filaments - BROKEN donut)
(moves up& down as actin filament polymerizes)
-FH1 domain binds profilin-actin
(slender arms) - grab hold of actin & feed them on end of actin filament
formins can Add
> 10,000 monomers before detaching
Highly processive
protein responsible in producing the force that contracts stress fibres causing them shorten in length
MYOSIN
myosin
Protein that produces force on its own!!!!
-Motor proteins (Covert chemical energy (ATP) into mechanical work )
(phsophate release - Conformational change – swing lever arm = force )
myosin can…
think of croud surfing
what is cloud
what is singer
Translocate actin filaments across glass slide
Croud = myosin
Singer = actin filament
Actin glides with the help of myosin
myosin produce force in particular direction - which end?
tyr to move towards + end of actin filament
-leading edge = minus end
Myosin has many classes: we look at which class
class II for contraction
what happens to Non-muscle myosin-II
forms bundles that pull actin filaments inward
the contraction of how cells pull their back foot up
Myosin-II bundles contract actin arrays
-by pushing inward and outward
Different actin networks exist at front & back of cell , what are they
front = leading edge
-lamellopodia
back = stress fibres
-contractile bundles of Long linear actin filaments interspersed with non-muscle myosin II
howt o organize front & bind
They know which is front/back - they know where they are going
Dictyostelium
cell migration
Amoeba that aggregates with other amoeba when starved (“chemotaxis”)
Clump tgt –> makes fruiting body –> detaches to find another nutrient
Some cells sacrifice themselves to make fruiting body to find other some food
Individual Dictyostelium move toward
concentrated cyclic-AMP
Rho family GTPases Trigger 3 types of actin network
Stress fibers - back foot
Dominant active Rho
Lamellipodia - front foot out
Dominant active Rac
Filopodia – the product
Dominant active Cdc42
dominant active - trapped in active form (GTP form)
Rho GTPases translate
outside signals into changes in actin cytoskeleton
hwo does Rhode Island GTPase translate outside signals into changes in actin cytoskeleton
- receptor binds to extracelkular signal
- interact with GEF - factor that exchanges GTP
- Rhode Island GDP become activated to Rho GTP - will control actin cytoskeleton
-also has conformational change that aloows to interact with effector proteins that can regulate actin cytoskeleton
4.to turn OFF GTPase - interact with GAP
GEF – turns GTPase ON
GTP exchange factor
GAP – turns off GTPase activation
Rho – activates Formins – by relieving auto-inhibition
Makes stress fibers from actin
RBD – Rho binding domain
active Rho-GTP:
relieves auto inhibition of formins
FH1 – little arms
FH2 – ring shape
what is involved in nucleating filopodia &lamellipodia
Cdc42
Cdc42
- in active state - interact with WASp by bind to RBD
- activate WASp
- activate ARp2/3
4.nucleation of branched actin network
activate Arp2/3 by opening WASp
Cells need ALL … to move
3 Rho GTPases
lamellopodia - Rac
stress fibers - Rhode Island
Filopodia - Cdc42
Extracellular signals create zones of
different Rho activity
1.Cdc42 activation at the front - lead to actin filament assembly & tread milling
2. Front Rac activation – lead to Arp2/3 activation - lamellopodia formation
3. Back Rho activation – lead to myosin II activation
