lecture 7 Flashcards
what is cell movement & changes and cell shape a combo of
cell proliferation, cell movement, tissue shaping
what are cell proliferation, cell movement, tissue shaping driven by
changes to cytoskeleton –> actin, microtubules, intermediate filaments
why is cytoskeleton useful for developmental processes
can be remodeled
what does rapid remodeling of cytoskeleton under plasma membrane lead to
changes of shape & dynamics; appendages being extended/retracted, adhering to surface, applying force to move it
property of every cytoskeletal filament system
ability to completely remodel depending on what cell wants it to do
describe cytoskeleton
hella dynamic; very easily remodeled, can be directed to fall apart or polymerize
what is cell remodeling a result of
intracellular signaling telling cells to move or divide
what controls dynamic ability of cytoskeleton
signaling pathways input onto cytoskeletal proteins
why is there cytoskelteon
control cell shape, tracks for vesicular traffic, generate force, structural strength
what is cell shape direct reflection of
internal cytoskeletal structure in cell
describe tracks for vesicular traffic
cargo within cell needs to be moved from point A to point B or secreted; move thru vesicles move around cytoskeletal tracks
how does non-muscle generate force
stress fibers
what are stress fibers
filaments of actomyosin that generate contractile force
what helps actin generate force
actin motor protein myosin 2 (non muscle myosin)
what would happen w/o cytoskeleton in terms of structure
there would just be plasma membrane, cell would be delicate as a bubble (no structural strength)
what does cytoskeleton do for cells etc.
gives structural strength
what happens when cell makes contact w/ surface
acto-cytoskeleton & other cytoskeleton are reorganized in response to signaling (initiated from this contact)
what happens due to cytoskeletal systems being reorganized
cells attach (grab onto cell surface, pull & stretch themselves), flatten, polarize, start moving
what happens to cell after it attaches n shit
dramatic changes in cell shape
what happens when cell polarizes
can tell front from back
what else do cells use cytoskeleton for
to generate cellular force
describe force produced by cytoskeleton
small, cuz cell is tiny af
how can we tell cell is producing force
cells attach & pull on pillars
what happens is nothing/no cells are pulling on pillars
no force is applied, cells stand straight up and down
what happens if cells are contacting pillars
attaches to pillar thru integrin interactions, pulls on pillar towards cell
basically what is cell tryna do while attached to pillar
its trying to spread out, and this pulls on pillar
what is myosin 2
motor protein that generates contractile forces
what happens if you added chemical inhibitor to myosin 2
pillar would go back straight (no contractile force)
what is vimentin
intermediate filament protein
what happens if mutation in vimentin
intermediate filament network is much weaker, skin is less strongly held together
what happens if you apply force in normal intermediate filament netowrk
no problem, no injury
what happens if you apply force to mutated intermediate filament
structural strength is compromised, shear off layers of dermis, form blisters (detachment of layers of tissue)
why are filamentous systems so dynamic & able to remodeled so quickly
bonds that hold these components together are H bonds (non-covalent)
what does non-covalent bonds mean in this context
weaker than covalent bonds –> easier to take apart, easier to form back together
why are systems so malleable, able to take diff shapes & forms, undergo rapid changes in shape & function
H bonds & electrostatic interactions
describe actin
individual actin proteins/monomers that come together & polymerize to form actin filaments
what are actin monomers
actin proteins
describe shape of actin polymer
helical polymer; natural twist
describe diff variety of actin filament shapes
filaments that are bundled together, branched actin network, etc.
why can actin be found in diff places in network
due to diff actin binding proteins helping shape network
where are actin filaments in cell
throughout cell, but most highly [ ] in cortex
describe actin in microvilli
give structure and function to microvilli (luminal surface of epithelial cells lining intestines)
what is integrin
receptors for extracellular matrix that helps cell grab onto things
describe actin/integrin
integrin cluster at end of long bundle of actin
what do actomyosin filaments do to actin
filaments generate forces to pull on integrin cluster to transmit force fron network to extracellular environment
where are integrin clusters
where cell is attached to surface
how big is microtubules
largest of 3; –> formes hollow filament netowrk
what is microtubule monomer
tubulin
what do microtubules form
trafficking network; vesicles travel along filament to find plasma membrane where they exocytose
basically what do microtubules do
provide tracks for vesicles to move along
what is another function of microtubules
in cilia; also helps segregate chromosomes
what are intermediate filaments
in b/w microtubules & actin in terms of size
describe intermediate filaments
woven together appearance –> hella stretchiness
what does this woven/stretchiness mean
can withstand hella force w/o breaking (will bend & stretch, not break)
what are intermediate filaments important for
structural strength
examples of intermediate filament proteins
vimentin, keratin
what are lamins
class of intermediate filaments found in nucleus, gives nucleus structural strength
what do these filaments work together to do
more complex cellular functions like migration & cell division
describe chemistry of individual microtubules & actin filaments
polarized; ends are chemically diff. from each other –> plus end & minus end
what does microtubules’ polarity result in
apical-basal polarity in epithelial layer
where do minus ends go
toward apical surface
where does plus ends go
basolateral surface
what does way to segregate diff components of cell (plus/minus end) give rise to
diff functional structures within cell
what drives overall cell polarity
microtubules
what is actin polarization more important for
how forces are generated inside cell
are intermediate filaments polarized
no
describe stability of single protofilament/microtubules
thermally unstable; easy to remodel
describe stability of multiple protofilaments
thermally stable
why do we know what actin does from scientific POV
b/c when nature tries to kill us, does so by targeting actin cytoskeleton (stops respiration thru affecting contraction in diaphragm)
what 3 chemicals/metabolites inhibit actin function
latrunculin, cytochalasin B, phalloidin
what do latrunculin and cytochalasin B do
bind onto existing filaments and cause them to fall apart
why does causing actin filament to fall apart stop its function
actin is no longer gonna function if its not in filament form
what does phalloidin do
stabilizes actin to PREVENT it from falling apart
why is phalloidin bad
prevents actin filament from getting any larger; locks it in place
why is stabilizing or depolymerizing actin equally bad
systems need to be dynamic to function; need to grow AND shrink
are all three equally lethal
yea
what does latrunculin do specifically
depolymerizes thru binding actin subunits
what does cytochalasin B do specifically
depolymerizes; caps filament plus ends
describe how actin monomers join filaments (in terms of polarity)
plus end joins to minus end, minus end joins to plus end
will two monomers ever join plus end to plus end
never; it’s like magnets repelling
why does actin filament have plus and minus end
b/c polarity is maintained as filament grows since they come together in same orientation
describe polarity of monomers
intrinsic polarity, two diff ends
how do actin monomers come together
thru noncovalent bonds
what is buried inside monomer
nucleotide; ATP
what happens when monomer joins filament
ATP hydrolyzed to ATP
describe nucleotide on monomers
always bound, just goes from ATP to ADP
do microtubules have nucleotide
GTP
what is RDS of formation of actin filaments
nucleation
what happens when two actin monomers come together to form a dimer
unstable
what is needed for actin filament formation
three monomers come together (it favors having a 4th join)
what part of polymerization takes longest
start; b/c you wait for 3 monomers to randomly come together by chance
what is nucleation
formation of actin oligomers
what is nucleus of actin filament
trimer (b/c it favors formation of tetramer)
describe lag phase
correpsonds w/ nucleation
what happens initially
no growth; lag phase, waiting for 3 monomers to come tog.
why is nucleation lag phase
you need 3 monomers to come together before you get stable growth
what happens in growth phase
filaments spontaneously elongate
what happens when it reaches EQ
filaments don’t shrink but no longer grow
What is changing in test tube over time that causes shift from growth to equilibrium?
enough monomers means polymerization; monomers drop below critical concentration means it switches from growth to treadmilling or shrinking
what happens if you dump in new monomers in test tube in EQ phase
would re-initiate logarithmic growth until it reaches a new EQ phase, where [ ] of free monomers are depleted again
what does steady state situation/ EQ mean
Concentration drops as monomers are increasingly incorporated into filaments, growth is no longer possible because at that concentration, a monomer is just as likely to bind as it is to leave
what are ATP bound monomers likely to do
polymerize
what are ADP bound monomers likely to do
fall apart
what happens if you added monomers to upper part of test tube only
those filaments would start to grow but the ones at the bottom wouldn’t grow because the [ ] down there would be different
what happens after fist seed filament forms
monomers come together allowing for rapid growth/elongation
what happens as monomers increasingly incorporated into filaments
[ ] drops, growth is no longer possible b/c at that [ ] monomer is just as likely to bind as it is to leave (critical [ ])
what happens when it starts to polymerize/filament forms/binds together
triggers hydrolysis from ATP to ADP
what are actin dimers
unstable
what is magical moment for actin
3 monomers together –> rapid growth
what does length of time in polymerized form favor
ADP formation
longer actin protein is in filament, more likely
to have switched to ADP
when does actin filament grow until
until [ ] of monomers drops below critical conc.
what does below critical [ ] mean
no longer thermodynamically favorable for polymerization rxn to occur
what does critical [ ] mean
rate of monomer addition equals rate of monomer loss (equal # monomers coming on as leaving) –> steady state situation
critical [ ] of actin in test tube
0.1 micromolar
what does above 0.1 um mean
filaments grow
what does at 0.1 mean
filaments stay same size (steady state)
what does below 0.1 mean
filaments shrink, actin leaving is favored
what is actin [ ] inside cell
100 um; should mean that inside cell should all be filaments
why isn’t inside of a cell all filaments
other regulatory proteins prevent actin from polymerizing when signals aren’t being received to direct polymerization
in a test tube what determines whether actin filaments polymerize, depolymerize, treadmill
actin monomer concentration
slowest step of actin polymerization
nucleation phase (need 3 monomers to come together in space & time to get first stable oligomer)
what happens after lag phase
filament starts growing rapidly
what happens as concentration of available actin monomers falls
reaches critical concentration
what is critical concentration
exact [ ] of actin monomers where you have equal rate of addition as loss
are plus and minus ends of actin similar or different
chemically different; diff chem structure & strength of interactions
describe speed of plus end vs. minus end
plus end can grow/shrink 4x faster that minus end
does stuff happen quicker at plus end or minus end
plus end
what does a given [ ] of monomers favor
favors growth
does plus end grow and minus end shrink?
both grow, just plus end grows faster
why does plus end grow faster
things can join plus end 4x faster than at minus end
what happens above critical [ ] for plus & minus ends
above it they both grow, below they both shrink
is critical conc. same or diff for plus & minus ends
same
plus vs. minus end, growing /shrinking
when growing or shrinking plus end does it 4x faster than minus end
what does plus end of monomer bind to
minus end
what does minus end of monomer bind to
plus end
is minus end faster or slower for gaining + losing
slower
what happens when monomers are floating around
ATP bound
what happens when monomers are joined to a filament
ATP is hydrolyzed to ADP
monomers are being added quicker than what
than time is takes to hydrolyze ATP to ADP
what does ones to right of filament mean
have been in filament for less time
what does ones to left of filament mean
been part of filament for more time (b/c added faster at plus end)
what does distance along filament reflect
reflects how long they’ve been in filament
what does monomers who’ve been in filament longer mean
have enough time to hydrolyze ATP to ADP
what happens to monomers being added quickly (newer ones)
need a little more time after being added to go from ATP to ADP
what is ATP cap
fast growing end is gonna have an ATP cap; certain # of actin proteins at plus end that remains attached to ATP
which end has ATP cap
plus end (fast growing filament)
which end doesn’t have ATP cap
minus end
why does one end have ATP cap and other doesn’t
not just b/c they’re chemically different, it’s a different form of actin on either end (ATP at plus, ADP at minus)
what does faster addition at plus end mean
takes time to hydrolyze ATP to ADP, leads to ATP cap at plus end
why do plus and minus end have different critical concentrations
ATP actin is more likely to polymerize (cuz its ATP), while ADP actin more likely to leave
what is at plus end (what kind of actin)
ATP actin
what is at minus end
ADP actin
which critical conc. is smaller
critical conc. of ATP smaller than ADP actin
what is at minus end
addition isn’t favored, for a given [ ] of actin monomers it’ll stop being added at a higher conc. than plus end
what is at plus end
addition is favored, need to have less actin monomers available before it stops being added
what happens if you’re in between the range
particular conc. is less than critical conc. at minus end
what happens if [ ] is in between conc. of ATP and ADP
plus end grows, minus end shrinks –> treadmilling
what is treadmilling
in b/w critical conc. of minus end and plus end; minus end shrinks at same rate that plus end grows –> overall stays same length
which critical concentration is bigger
minus end
what does actin form
polarized filament w/ distinct chem properties at each end
what does nucleotide hydrolysis lead to
treadmilling
what is slowest step of actin polymerization
oligomer formation
