cytoskeleton and cell motility ch17 Flashcards
when you look at moving cells what should you notice
there is a clear area called a “leading zone”; there are differences in rate of motility;
what are some examples of cell crawling
gastrulation; immune responses; growth cones of neuronal devpmt; wound healing; bone devpmt; cancer cell metastasis
what are the two filaments that we care about
actin and microtubules. these two are more dynamic
what makes actin filaments
two strands of subunits “two strings of pearls with a regular repeat of subunits” diameter is small (5-7nm)
G actin is made of the globular actin monomer
what is the barbed end?
the + end that likes to grown on actin and add subunits; it ends atp loaded actin, the other end is out of energy (adp) and it falls off
in a test tube, if you put actin in a tube what happens
it has a rate limiting step called nucleation. you need the first trimer of subunits in order for the rest of the filament to form. This is probably the control point for whether or not you build new muscle
what is treadmilling
the balance, at equilibrium, of addition on the barbed end and loss on the pointed end. while the pieces and parts are changing out, the net length of the strand remains the same
describe the concentration of free monomer during treadmilling
“will be between Cc for plus and minus ends”
what are some actin binding proteins?
tropomyosin (side binding molecule to regulate myosin); profilin; capping protein; arp; formin;
profilin function? binds to?
binds to monomeric actin; it is a sequestering monomer that holds onto actin to keep it near a forming filament
what is profillin function on monomeric actin
acts like a GEF on monomeric actin. its a control point
ADF/cofilin function? binds to?
this causes disassembly of actin; binds to ADP actin (both monomer and polymer); cause breaks in the filament back bone by altering the twist of the filament
when used together, what do ADF/cofillin and profilin do?
maybe catalyzes treadmilling; profilin adds, cofilin takes away
what is capping protein bind?
bind the barbed end of actin (cap Z= the z line of the sarcomere) and pointed end of actin (tropomodulin)
when the cap Z binds to the positive end of actin what happens?
it stabalizes actin, doesn’t disassemble or add new pieces
what is the rate limiting step of actin filaments?
the nucleation
what proteins can generate nucleation factors?
ARP2/3 complex and Formin; there are more but these are the two famous ones
what does arp stand for
actin related protein
Describe the ARP complex
heptameric complex; they are separated; when activated then ARP 2 and 3 are brought together as the first two subunits of the activated helix.
where do ARP prefer to do their thang?
they prefer to activate by binding a mother filament at a 70 degree angle “tends to generate branched networks that look like a dendritic branch array”
when the actin filament grows, which end will you see the arp on?
the negative end
formins: make what kind of complex
binds a monomer that makes a donut of two subunits using an FH2 domain (each subunit binds one monomer)
what is another property of formins?
the donut associates with the PLUS end and it STAYS there while it GROWS; it ratchets down the growing filament as polymer assembly occurs
what is a name/class for formin
processive assembly factor
when formin attaches, what happens to the assembly of actin filaments
it goes WAAAY faster, and they are long, straight filaments that can make cable-like things
compare and contrast arp and formin structures that are made? where would you find them?
arp makes a net (think leading edge), formin makes a cable of actin (think stress fiber)
how is this actin idea related to anything useful?
by controlling actin filaments you can control the movement of a cell
myosin
large complex molecules; skeletal, cardiac muscle guy (myosin II)
what are some things that can vary between different types of myosin?
they have terminal regions that have different binding specifications. they have differnet lengths of coiled coils
when you die, why do your muscles get hard?
myosin needs ATP to release its binding to the actin filament
myosin crawls toward which end of the actin filament?
all myosins (with one exception) walk to the BARBED (PLUS) end; because remember, the z disk is the plus end and the distance between them shortens during contraction
what is another jobs that myosin can do?
transport vessicles
what are the three cycles of cell migration? what should you remember controls this?
protrusion, adhesion, retraction; you have to have a traction force (using focal adhesion sites of integrins) to link the cell to the extracellular matrix; actin control helps regulate this
lamellapodium is? has?
dendritic branched array on leading edge that has filopodium.
filopodium is?
parallel bundles that sense where to go
stress fibers made of?
parallel fibers (formin)
what to GEFS and GAPS do in this context?
actin organization -> Rho that belongs to Gproteins, along with Rac and Cdc42
rho generates
stress fibers. rho rho rho your boat gently down the stream
cdc42 mades
filopodia actin bundles. porcupine
rac makes
things. actually they make lamellopodia (actin in periphery)
how do we know that rho, rac, cdc42 make different things?
if you starve fibroblasts of serum and then pump them full with a constituitively active Gprotein, you’ll see something different.
rac, rho and cdc42 are control points that activate____
rho does formins for actin polymerization
rac does arp2/3 for actin polymerization
cdc also is arp 2/3
***these give the cell polarity
what is the key protein of focal adhesions? what do they do
on the outside, integrins bind to substratum. on the inside, they attach to tain, alpha actinin, vinculin, and something else
what is a function/event in the leading edge of a crawling cell?
treadmilling! but this time, its not one polymer treadmilling, but the whole actin network.
how does a locomoting cell use arp 2/3?
it is IN lamellapodium, but that doesn’t mean its DOING something
how does a ruffling, leading edge function?
all the players, all the things, control actin assembly, disassembly in the leading edge of the lamellapodium to generate a bunch of things to push on the leading edge
gotta turn on rac, arp 2/3 that makes a new site for filament formation, adds on profilin on free barbed end until the capping protein comes along and stops the growth.
if you are adp loaded, what protein would like to eat you?
the ADP/cofilin
what things regulate the actin polymerization of a leading edge?
phospholipids, calcium
pathogens are ___. listeria causes ___ by taking over___
clever. listeria causes bad GI problems it takes over the nucleation factor machine to bast itself through the cell membrane into the next cell.
what does lady shigella do?
she recruits host cell arp2/3 complex to generate a new actin array
the locomotion part of cells is important for what kinds of processes?
immunity, pathogens, virus infection. cell machinery is a important vulnerable point for bad things to get in
how do cells steer?
gradients, signalling.
