lecture 7 Flashcards
1
Q
what is cell movement & changes and cell shape a combo of
A
cell proliferation, cell movement, tissue shaping
2
Q
what are cell proliferation, cell movement, tissue shaping driven by
A
changes to cytoskeleton –> actin, microtubules, intermediate filaments
3
Q
why is cytoskeleton useful for developmental processes
A
can be remodeled
4
Q
what does rapid remodeling of cytoskeleton under plasma membrane lead to
A
changes of shape & dynamics; appendages being extended/retracted, adhering to surface, applying force to move it
5
Q
property of every cytoskeletal filament system
A
ability to completely remodel depending on what cell wants it to do
6
Q
describe cytoskeleton
A
hella dynamic; very easily remodeled, can be directed to fall apart or polymerize
7
Q
what is cell remodeling a result of
A
intracellular signaling telling cells to move or divide
8
Q
what controls dynamic ability of cytoskeleton
A
signaling pathways input onto cytoskeletal proteins
9
Q
why is there cytoskelteon
A
control cell shape, tracks for vesicular traffic, generate force, structural strength
10
Q
what is cell shape direct reflection of
A
internal cytoskeletal structure in cell
11
Q
describe tracks for vesicular traffic
A
cargo within cell needs to be moved from point A to point B or secreted; move thru vesicles move around cytoskeletal tracks
12
Q
how does non-muscle generate force
A
stress fibers
13
Q
what are stress fibers
A
filaments of actomyosin that generate contractile force
14
Q
what helps actin generate force
A
actin motor protein myosin 2 (non muscle myosin)
15
Q
what would happen w/o cytoskeleton in terms of structure
A
there would just be plasma membrane, cell would be delicate as a bubble (no structural strength)
16
Q
what does cytoskeleton do for cells etc.
A
gives structural strength
17
Q
what happens when cell makes contact w/ surface
A
acto-cytoskeleton & other cytoskeleton are reorganized in response to signaling (initiated from this contact)
18
Q
what happens due to cytoskeletal systems being reorganized
A
cells attach (grab onto cell surface, pull & stretch themselves), flatten, polarize, start moving
19
Q
what happens to cell after it attaches n shit
A
dramatic changes in cell shape
20
Q
what happens when cell polarizes
A
can tell front from back
21
Q
what else do cells use cytoskeleton for
A
to generate cellular force
22
Q
describe force produced by cytoskeleton
A
small, cuz cell is tiny af
23
Q
how can we tell cell is producing force
A
cells attach & pull on pillars
24
Q
what happens is nothing/no cells are pulling on pillars
A
no force is applied, cells stand straight up and down
25
what happens if cells are contacting pillars
attaches to pillar thru integrin interactions, pulls on pillar towards cell
26
basically what is cell tryna do while attached to pillar
its trying to spread out, and this pulls on pillar
27
what is myosin 2
motor protein that generates contractile forces
28
what happens if you added chemical inhibitor to myosin 2
pillar would go back straight (no contractile force)
29
what is vimentin
intermediate filament protein
30
what happens if mutation in vimentin
intermediate filament network is much weaker, skin is less strongly held together
31
what happens if you apply force in normal intermediate filament netowrk
no problem, no injury
32
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)
33
why are filamentous systems so dynamic & able to remodeled so quickly
bonds that hold these components together are H bonds (non-covalent)
34
what does non-covalent bonds mean in this context
weaker than covalent bonds --> easier to take apart, easier to form back together
35
why are systems so malleable, able to take diff shapes & forms, undergo rapid changes in shape & function
H bonds & electrostatic interactions
36
describe actin
individual actin proteins/monomers that come together & polymerize to form actin filaments
37
what are actin monomers
actin proteins
38
describe shape of actin polymer
helical polymer; natural twist
39
describe diff variety of actin filament shapes
filaments that are bundled together, branched actin network, etc.
40
why can actin be found in diff places in network
due to diff actin binding proteins helping shape network
41
where are actin filaments in cell
throughout cell, but most highly [ ] in cortex
42
describe actin in microvilli
give structure and function to microvilli (luminal surface of epithelial cells lining intestines)
43
what is integrin
receptors for extracellular matrix that helps cell grab onto things
44
describe actin/integrin
integrin cluster at end of long bundle of actin
45
what do actomyosin filaments do to actin
filaments generate forces to pull on integrin cluster to transmit force fron network to extracellular environment
46
where are integrin clusters
where cell is attached to surface
47
how big is microtubules
largest of 3; --> formes hollow filament netowrk
48
what is microtubule monomer
tubulin
49
what do microtubules form
trafficking network; vesicles travel along filament to find plasma membrane where they exocytose
50
basically what do microtubules do
provide tracks for vesicles to move along
51
what is another function of microtubules
in cilia; also helps segregate chromosomes
52
what are intermediate filaments
in b/w microtubules & actin in terms of size
53
describe intermediate filaments
woven together appearance --> hella stretchiness
54
what does this woven/stretchiness mean
can withstand hella force w/o breaking (will bend & stretch, not break)
55
what are intermediate filaments important for
structural strength
56
examples of intermediate filament proteins
vimentin, keratin
57
what are lamins
class of intermediate filaments found in nucleus, gives nucleus structural strength
58
what do these filaments work together to do
more complex cellular functions like migration & cell division
59
describe chemistry of individual microtubules & actin filaments
polarized; ends are chemically diff. from each other --> plus end & minus end
60
what does microtubules' polarity result in
apical-basal polarity in epithelial layer
61
where do minus ends go
toward apical surface
62
where does plus ends go
basolateral surface
63
what does way to segregate diff components of cell (plus/minus end) give rise to
diff functional structures within cell
64
what drives overall cell polarity
microtubules
65
what is actin polarization more important for
how forces are generated inside cell
66
are intermediate filaments polarized
no
67
describe stability of single protofilament/microtubules
thermally unstable; easy to remodel
68
describe stability of multiple protofilaments
thermally stable
69
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)
70
what 3 chemicals/metabolites inhibit actin function
latrunculin, cytochalasin B, phalloidin
71
what do latrunculin and cytochalasin B do
bind onto existing filaments and cause them to fall apart
72
why does causing actin filament to fall apart stop its function
actin is no longer gonna function if its not in filament form
73
what does phalloidin do
stabilizes actin to PREVENT it from falling apart
74
why is phalloidin bad
prevents actin filament from getting any larger; locks it in place
75
why is stabilizing or depolymerizing actin equally bad
systems need to be dynamic to function; need to grow AND shrink
76
are all three equally lethal
yea
77
what does latrunculin do specifically
depolymerizes thru binding actin subunits
78
what does cytochalasin B do specifically
depolymerizes; caps filament plus ends
79
describe how actin monomers join filaments (in terms of polarity)
plus end joins to minus end, minus end joins to plus end
80
will two monomers ever join plus end to plus end
never; it's like magnets repelling
81
why does actin filament have plus and minus end
b/c polarity is maintained as filament grows since they come together in same orientation
82
describe polarity of monomers
intrinsic polarity, two diff ends
83
how do actin monomers come together
thru noncovalent bonds
84
what is buried inside monomer
nucleotide; ATP
85
what happens when monomer joins filament
ATP hydrolyzed to ATP
86
describe nucleotide on monomers
always bound, just goes from ATP to ADP
87
do microtubules have nucleotide
GTP
88
what is RDS of formation of actin filaments
nucleation
89
what happens when two actin monomers come together to form a dimer
unstable
90
what is needed for actin filament formation
three monomers come together (it favors having a 4th join)
91
what part of polymerization takes longest
start; b/c you wait for 3 monomers to randomly come together by chance
92
what is nucleation
formation of actin oligomers
93
what is nucleus of actin filament
trimer (b/c it favors formation of tetramer)
94
describe lag phase
correpsonds w/ nucleation
95
what happens initially
no growth; lag phase, waiting for 3 monomers to come tog.
96
why is nucleation lag phase
you need 3 monomers to come together before you get stable growth
97
what happens in growth phase
filaments spontaneously elongate
98
what happens when it reaches EQ
filaments don't shrink but no longer grow
99
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
100
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
101
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
102
what are ATP bound monomers likely to do
polymerize
103
what are ADP bound monomers likely to do
fall apart
104
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
105
what happens after fist seed filament forms
monomers come together allowing for rapid growth/elongation
106
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 [ ])
107
what happens when it starts to polymerize/filament forms/binds together
triggers hydrolysis from ATP to ADP
108
what are actin dimers
unstable
109
what is magical moment for actin
3 monomers together --> rapid growth
110
what does length of time in polymerized form favor
ADP formation
111
longer actin protein is in filament, more likely
to have switched to ADP
112
when does actin filament grow until
until [ ] of monomers drops below critical conc.
113
what does below critical [ ] mean
no longer thermodynamically favorable for polymerization rxn to occur
114
what does critical [ ] mean
rate of monomer addition equals rate of monomer loss (equal # monomers coming on as leaving) --> steady state situation
115
critical [ ] of actin in test tube
0.1 micromolar
116
what does above 0.1 um mean
filaments grow
117
what does at 0.1 mean
filaments stay same size (steady state)
118
what does below 0.1 mean
filaments shrink, actin leaving is favored
119
what is actin [ ] inside cell
100 um; should mean that inside cell should all be filaments
120
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
121
in a test tube what determines whether actin filaments polymerize, depolymerize, treadmill
actin monomer concentration
122
slowest step of actin polymerization
nucleation phase (need 3 monomers to come together in space & time to get first stable oligomer)
123
what happens after lag phase
filament starts growing rapidly
124
what happens as concentration of available actin monomers falls
reaches critical concentration
125
what is critical concentration
exact [ ] of actin monomers where you have equal rate of addition as loss
126
are plus and minus ends of actin similar or different
chemically different; diff chem structure & strength of interactions
127
describe speed of plus end vs. minus end
plus end can grow/shrink 4x faster that minus end
128
does stuff happen quicker at plus end or minus end
plus end
129
what does a given [ ] of monomers favor
favors growth
130
does plus end grow and minus end shrink?
both grow, just plus end grows faster
131
why does plus end grow faster
things can join plus end 4x faster than at minus end
132
what happens above critical [ ] for plus & minus ends
above it they both grow, below they both shrink
133
is critical conc. same or diff for plus & minus ends
same
134
plus vs. minus end, growing /shrinking
when growing or shrinking plus end does it 4x faster than minus end
135
what does plus end of monomer bind to
minus end
136
what does minus end of monomer bind to
plus end
137
is minus end faster or slower for gaining + losing
slower
138
what happens when monomers are floating around
ATP bound
139
what happens when monomers are joined to a filament
ATP is hydrolyzed to ADP
140
monomers are being added quicker than what
than time is takes to hydrolyze ATP to ADP
141
what does ones to right of filament mean
have been in filament for less time
142
what does ones to left of filament mean
been part of filament for more time (b/c added faster at plus end)
143
what does distance along filament reflect
reflects how long they've been in filament
144
what does monomers who've been in filament longer mean
have enough time to hydrolyze ATP to ADP
145
what happens to monomers being added quickly (newer ones)
need a little more time after being added to go from ATP to ADP
146
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
147
which end has ATP cap
plus end (fast growing filament)
148
which end doesn't have ATP cap
minus end
149
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)
150
what does faster addition at plus end mean
takes time to hydrolyze ATP to ADP, leads to ATP cap at plus end
151
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
152
what is at plus end (what kind of actin)
ATP actin
153
what is at minus end
ADP actin
154
which critical conc. is smaller
critical conc. of ATP smaller than ADP actin
155
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
156
what is at plus end
addition is favored, need to have less actin monomers available before it stops being added
157
what happens if you're in between the range
particular conc. is less than critical conc. at minus end
158
what happens if [ ] is in between conc. of ATP and ADP
plus end grows, minus end shrinks --> treadmilling
159
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
160
which critical concentration is bigger
minus end
161
what does actin form
polarized filament w/ distinct chem properties at each end
162
what does nucleotide hydrolysis lead to
treadmilling
163
what is slowest step of actin polymerization
oligomer formation
