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lecture 9 Flashcards

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1
Q

besides actin what are 3 other cytoskeletal systems in cells

A

microtubules, intermediate filaments, septins

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2
Q

what is associated w/ lamellipodia

A

Arp 2/3

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3
Q

major function of intermediate filaments

A

provides structure and strength to cells and tissues

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4
Q

what can intermediate filaments connect to

A

actin

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5
Q

are microtubules dynamic

A

hella dynamic

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6
Q

where are minus ends of microtubules

A

found at centrosomes, where they are nucleated

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7
Q

where are plus ends of microtubules

A

radiate away from centrosomes, towards leading edge of this migrating cell (in this example)

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8
Q

what do plus ends of microtubules do

A

program where the leading edge is gonna go

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9
Q

what would happen if microtubules were growing in a diff direction

A

leading edge would switch and re-position to where microtubules were found

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10
Q

what is polarity of microtubules important for

A

dictating overall polarity of cell

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11
Q

describe polarity of microtubules

A

minus ends toward cell center, plus ends toward leading edge of cell plasma membrane

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12
Q

why do microtubules have dramatic effect on cell structure & function

A

plus ends direct where signaling molecules go & are activated –> generates lamellipodial actin that makes leading edge AND tracks for vesicles w cargo (toward leading edge)

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13
Q

what 2 things does polarized microtubules lead to

A

polarized signaling and polarized trafficking/secretion (both important for cells to move in a certain direction)

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14
Q

what is the brains of operation

A

microtubules

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15
Q

are intermediate filaments rlly dynamic

A

not really; kinda slower turnover

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16
Q

what do intermediate filaments do

A

provide structural strength & form physical barriers

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17
Q

what important thing can intermediate filaments do

A

can segregate one part of cytoplasm from another, form a cytoskeletal wall (thru bulk)

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18
Q

are intermediate filaments static or dynamic

A

relatively static (compared to microtubules & actin)

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19
Q

are intermediate filaments polarized

A

no; chemically identical

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20
Q

can intermediate filaments be used to traffic things?

A

no, because there’s no inherent directionality, nothing to tell motors moving vesicles which way to go

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21
Q

what else do intermediate filaments do

A

provide structural strength

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22
Q

what are 3 chemicals that affect microtubules

A

taxol, nocodazole, colcichine

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23
Q

what does taxol do

A

stabilizes microtubules, locking them into that configuration

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24
Q

what is a medical application of taxol

A

chemotherapy; kills rapidly dividing cancer cells by stabilizing & disrupting their microtubules

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25
Q

what do nocodazole and colchicine do

A

cause microtubule depolymerization –> cause them to fall apart

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26
Q

which chemicals depolymerize

A

nocodazole, colchicine

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27
Q

which chemicals stabilize

A

taxol

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28
Q

which is worse, stabilizer or depolymerizer of microtubules

A

both are equally bad; b/c dynamics (growing AND shrinking) are essential for health and function

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29
Q

what is microtubule subunit

A

tubulin protein

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30
Q

how does actin float around as

A

monomer

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31
Q

how does tubulin exist

A

as a heterodimer

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32
Q

how many genes is tubulin expressed from

A

3 diff genes –> 3 diff proteins

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33
Q

what are 2 distinct proteins in tubulin

A

alpha tubulin and beta tubulin

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34
Q

what are building blocks that create microtubules built up from

A

stable heterodimers that consist of 1 b-tubulin bound to 1 a-tubulin

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35
Q

are you ever gonna find alpha and beta tubulin by themselves?

A

no; always together in cytoplasm

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36
Q

what polymerizes to form the large diameter microtubules

A

tubulin heterodimer

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37
Q

describe association/interactions of actin that give rise to helical filaments

A

head to tail associations

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38
Q

describe associations of alpha-beta tubulin

A

head to tail interactions AND lateral associations w/ neighboring heterodimers

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39
Q

what do these lateral associations allow microtubules to do

A

not just make filament structure but also the hollow tube that is fully formed microtubule

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40
Q

what gives rise to hollow cylinder that is microtubule

A

head to tail associations AND lateral associations

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41
Q

what does plus end bind to

A

minus end

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42
Q

how do alpha and beta tubulin bind to

A

plus end of beta tubulin, minus end of beta tubulin binds to plus end of alpha tubulin, minus end of alpha tubulin (at bottom of screen)

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43
Q

what nucleotides are tubulin heterodimers bound to (like actin monomers)

A

guanine

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44
Q

where are nucleotides located on tubulin heterodimer

A

one copy at plus end of beta tubulin, second copy at plus end of alpha tubulin

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45
Q

what happens to nucleotide (GTP) on beta tubulin

A

hydrolyzes after joining the growing filament

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46
Q

what happens to nucleotide on alpha tubulin

A

buried in the dimer; has no role in subsequent filament dynamics

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47
Q

when we talk about GTP hydrolysis, what does it refer to

A

nucleotide on beta tubulin

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48
Q

is this (GTP to GDP) a hydrolysis or exchange

A

hydrolysis, not an exchange

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49
Q

what has activity to hydrolyze GTP to GDP, and how is it triggered

A

tubulin has the activity, and it’s triggered by polymerization (like actin)

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50
Q

what happens after tubulin is added to a filament

A

internal chemical timer starts, after milliseconds it is hydrolyzed to GTP

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51
Q

what does GTP form like

A

it likes being in a filament, favors polymerization

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52
Q

what does GDP form like

A

doesn’t wanna be in filament anymore (like actin)

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53
Q

what does the ATP to ADP switch in actin do

A

gives rise to treadmilling

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54
Q

what does hydrolysis of GTP to GDP in microtubules do

A

dictates whether it’s gonna be growing or switching to shrinking (dynamic instability)

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55
Q

what is dynamic instability, and what is it a direct result of

A

ability for MT to switch from growing to shrinking to growing again; result of hydrolysis of GTP on beta tubulin

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56
Q

do we need to worry about minus end of microtubules

A

no; everything is plus end, can ignore minus end b/c minus ends are all anchored into centrosomes where they are nucleated

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57
Q

in a rapidly growing microtubule what is there at plus end

A

GTP cap

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58
Q

when does GTP cap form

A

growing polymer, where heterodimers are added so fast they don’t have time to hydrolyze GTP to GDP (unlike the other side who has been there longer)

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59
Q

what is length of filament correlated w/

A

how long heterodimers have been in filament

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60
Q

what does it mean as long as there’s abundant GTP bound heterodimers to be added to plus ends

A

it’s gonna keep growing

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61
Q

how does it lose GTP cap

A

supply of GTP bound heterodimers runs low (whether random or regulated), not added as quickly, they have time to hydrolyze GTP to GDP before another heterodimer is added –> loss of GTP cap

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62
Q

what happens after loss of GTP cap

A

all becomes GDP tubulin, which likes to fall apart (doesn’t like to be polymerized in a MT –> rapid collapse)

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63
Q

what does GTP cap do

A

holds the microtubule together, allows more heterodimers to be added

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64
Q

describe dynamic instability in context of GTP/GDP

A

loss of GTP cap means you can’t add GTP bound monomers as quickly, so filament switches from growing to rapidly shrinking

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65
Q

is dynamic instability reversible?

A

no; doesn’t lead to destruction of entire molecule

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66
Q

how can it switch b/w growing and shrinking

A

linked to [ ] of GTP bound heterodimers; if more GTP bound MTs are available, goes from shrinking to growing

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67
Q

how do MTs switch from growing to shrinking and back

A

based on availability of GTP cap

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68
Q

what is catastrophe

A

switches from growing to shrinking

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69
Q

what is rescue

A

switches back to growing [enough GTP bound heterodimers added –> GTP cap is established]

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70
Q

what is GTP bound to

A

beta tubulin in polymerized form

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71
Q

what happens when the heterodimer is released from filament

A

it takes GDP with it

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72
Q

why is rescue, catastrophe, growing/shrinking so important

A

MTs need to get to different spots quickly, need to sample diff areas/parts of cell {being stuck in one spot is bad}

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73
Q

what does growing shrinking allow

A

can go from where leading edge is to where leading edge is gonna be next –> key to their ability to steer & control cells, organization, cell function

74
Q

why does GDP form of tubulin wanna leave polymer so badly

A

after hydrolysis, subtle shift in conformation that weakens bond b/w adjacent heterodimers (can see slight curvature to filament)

75
Q

what does conformational change do

A

decreases affinity of adjacent heterodimers for each other (curve)

76
Q

what happens once GTP cap is lost

A

they are primed to fall apart

77
Q

what happens once heterodimer is released

A

GDP to GTP exchange in cytoplasm, recycled and ready to be reincorporated

78
Q

what does the GTP cap represent

A

high affinity interactions; want to stay together, rapidly growing MT

79
Q

what does losing cap represent

A

weakened affinity, due to chemical shift (change from GDP to GTP), just fall apart

80
Q

how does it fall apart?

A

chunks peel away as it shrinks, not individual monomers)

81
Q

what is crucial for MT function

A

ability to switch from growing to shrinking and back again

82
Q

what dictates whether you’re growing or shrinking at plus end

A

rate of addition of monomers

83
Q

what end of MT is this going on

A

all at plus end

84
Q

how many monomers does actin oligomer need

A

3

85
Q

how many tubulin heterodimers needed

A

7!!!! also needa come together in a spiral structure

86
Q

what machinery helps overcome these challenges/conditions

A

template that holds tubulin in exact right position –> can have heterodimers at right place & time, so you can add new heterodimers to get that growth

87
Q

why do you need a protein cmplex

A

need it to nucleate new filaments by holding blocks in scaffold, so you don’t need to take time for them to randomly come together in right orientation

88
Q

what is the 3d tubulin

A

gamma-tubulin small complex

89
Q

what are first 2 tubulins

A

alpha and beta tubulin which forms heterodimer –> gonna get added to growing fliament

90
Q

where is gamma tubulin found

A

only at sites of microtubule nucleation

91
Q

what does gamma tubulin form

A

scaffold that additional alpha-beta tubulins can be added to

92
Q

how many actin homologs in arp 2/3

A

2 actin homologs

93
Q

how many tubulins for gamma tubulin

A

7 copies –> 14 tubulins held in right place to initiate spiral structure

94
Q

what is job of gamma tubulin small complex

A

initiate spiral structure that alpha and beta tubulin can be added to, to get a functioning microtubule

95
Q

what is the only place that gamma tubulin has a function in cell

A

here; sites of MT nucleation

96
Q

what do accessory proteins do

A

hold them at right location, makes sure it happens at centrosome

97
Q

where specifically are gamma tubulin small complexes found

A

centrosomes

98
Q

where are all MTs growing out from

A

one locatino

99
Q

what is centrosome packed w/

A

packed w/ gamma tubulin ring complexes

100
Q

what is centrosome

A

pair of centrioles, duplicated during cell division & evenly distributed among daughter cells

101
Q

what is centrosome / pair of centrioles surrounded by

A

pericentriolar material

102
Q

what do gamma tubulin small complexes bind to

A

pericentriolar material

103
Q

where do MTs grow away from

A

centrosome

104
Q

where are plus and minus ends

A

plus ends grow away, minus ends are attached & locked to centrosome

105
Q

where is minus end gonna be always

A

anchored to centrosome via gamma tubulin nucleating complex (unless it depolymerizes totally)

106
Q

what 3 proteins control microtubule dynamics (contribute to whether it grows or shrinks)

A

stathmin, kinesin-13, XMAP215

107
Q

what is stathmin

A

analogous to thymosin for actin; grabs & binds heterodimers, prevents them from being added to plus end

108
Q

what dose stathmin promote

A

shrinking; catastrophe

109
Q

what is kinesin-13

A

microtubule motor; don’t walk along MTs, but use thats systems to rip them apart & induce catastrophe

110
Q

what are kinesins

A

protein complexes that use power of ATP hydrolysis to walk along MTs

111
Q

how many copies of Kinesin-13 do we see on plus end of MT

A

4 copies on plus end of MT

112
Q

what is XMAP215

A

plus end protein that does opposite –> stabilizes plus ends, harder time falling apart

113
Q

when does XMAP215 stabilize plus end until

A

GTP tubulin recovers and keeps on going

114
Q

what is plectin

A

protein that connects microtubules (also actin) to other structures -> intermediate filaments

115
Q

what does plectin do specifically

A

connects MTs to intermediate filaments

116
Q

what do catastrophe & stabilization factors do

A

both target GTP-bound tubulin dimers at plus end of polymer

117
Q

what does kinesin 13 do

A

induces depolymerization (even if cap is there)

118
Q

what happens if cell needs MT to shrink but doesn’t have time to get rid of GTP cap

A

kinesin 13!!!

119
Q

what is XMAP215

A

opposite; accelerates growth & promotes MT polymerization

120
Q

what does stathmin do

A

binds to heterodimers & prevents them from being added to plus end

121
Q

what happens if you have a bunch of active stathmin around

A

reduces [ ] of available heterodimers, you get catastrophe & shrinking

122
Q

what does thymosin bind to

A

1 actin monomer

123
Q

what does stathmin bind to

A

2 heterodimers

124
Q

what motor protein for actin

A

myosin 2 (generates contractile force)

125
Q

what motor protein for MTs

A

kinesin 1

126
Q

what do motor proteins do for MT

A

move cargo from one end of cell to another

127
Q

describe kinesin 1

A

looks like myosin 2 (long tail that wraps around neighbor –> extended coil coil)

128
Q

what is structure of kinesin

A

functional dimer, 2 globular motor domains

129
Q

what are globular motor domains responsible for

A

responsible for binding & unbinding to microtubule filament to walk from minus end toward plus end

130
Q

what does kinesin 1 mean for vesicles

A

you have a vesicle, starts at center of cell, moves toward cell edge

131
Q

how can you infer kinesin 1 is dragging it along a polarized MT or centrosome

A

go from where minus ends are to cell membrane where plus ends are

132
Q

what is mechanism for kinesin 1

A

driven by ATP hydrolysis

133
Q

where is leading head closer to

A

closer to plus end (b/c that’s drxn MT is walking)

134
Q

what is next step

A

leading head is bound ADP, lagging head is bound to ATP

135
Q

what happens after ATP is hydrolyzed on lagging head

A

phosphate is released from lagging head –> lagging head is released, conformational change at neck region of motor protein, leads to lagging head stepping over leading head and essentially becomes leading head

136
Q

what switches

A

leading head becomes lagging head

137
Q

what happens at the end

A

end up in exact same spot where you started cycle; leading head is ADP bound, lagging head ATP bound

138
Q

what does hinge region have

A

flexibility, allows them to step over each other

139
Q

describe myosin 2

A

contracts filaments in opposite drxns b/c heads are facing each other in bipolar filaments

140
Q

what is stationary and what is moving in myosin

A

myosin motor protein is stationary, actin is slid/moving

141
Q

what is stationary and moving in MT

A

microtubule is stationary, motor protein is walking on it

142
Q

which 2 motor proteins move along MTs

A

kinesin 1, (cytoplasmic) dynein

143
Q

is dynein smaller or bigger than kinesin

A

way bigger & complicated

144
Q

what is kinesin

A

motor domains that walk along filament, long tails are connected to vesicles/cargo

145
Q

what are kinesins doing/have as they walk towards plus end filament

A

carrying something w/ them

146
Q

what about dynein

A

binds to cargo, carries cargo on one end, other end walks along microtubule

147
Q

describe dynein

A

cargo bound motor protein, goes from plus end to minus end

148
Q

what if cell wants to get stuff into cell (endocytic event)

A

gonna attach to dynein so it can walk opposite drxn where all minus ends are in cell’s nucleus

149
Q

basically what to know about dynein

A

cargo carrying motor protein that goes to minus ends of MTs

150
Q

where does kinesin walk to

A

walks toward plus end of MTs

151
Q

first step of intermediate filament assembly

A

start w/ intermediate filament monomer, forms alpha helix –> has amino terminus (N terminus) and carboxy terminus (C terminus) like any other protein

152
Q

what is next step

A

2 monomers come together to form a coiled coil dimer (alpha helices wrap around each other to form coiled-coil)

153
Q

what happens when coiled coil dimer is formed

A

amino termini are lined up, carboxy termini are lined up –> dimers are also polarized

154
Q

next step

A

2 dimers come together to form a staggered tetramer –> polarity is lost

155
Q

described the tetramer

A

non-polarized

156
Q

what happens next

A

lateral association of 8 tetramers. (unpolarized)

157
Q

what happens once 8 tetramers come together

A

can be added to growing filament

158
Q

what is final result at end of the day

A

non-polarized filament, no plus or minus end

159
Q

why would a motor protein not know where to go

A

b/c no directionality; that’s why there’s no known motor proteins that interact w/ intermediate filaments

160
Q

why are intermediate filaments so strong and hard to break

A

woven together like a rope

161
Q

describe associations of intermediate filaments

A

head to tail associations but many MORE lateral associations –> can stretch w/o breaking

162
Q

describe associations of actin filaments

A

head to tail monomer formation

163
Q

describe associations of MTs

A

head to tail w/ some lateral associations

164
Q

describe defect/mutation in intermediate filaments (keratin)

A

lost structural integrity; if they rub hands together, form blisters b/c no resistance to force

165
Q

describe dynamic of intermediate filaments

A

dynamic but slower than actin

166
Q

what does plectin do

A

links MTs and intermediate filaments –> hybrid cytoskeletal structure

167
Q

what is one function of cytoskeletal cross-linking

A

connects diff parts of cells into one continuous mechanical network

168
Q

what is intermediate filaments in nuclear lamina

A

line inner surface of nuclear envelope, gives nucleus structural strength

169
Q

what are cross linking proteins that connect nuclear skeleton to cytoskeleton in cytoplasm

A

KASH and SUN proteins

170
Q

what to know

A

when you look at cell, there’s interconnected filament system from nuclear skeleton to cytoskeleton bridged by KASH and SUN domain containing proteins

171
Q

on test, ex. of why you’d want cytoskeletal elements to be connected

A

top is fibroblast that’s migrated thru dense ECM (filamentous protein network that’s glue that holds tissues together)

172
Q

what do fibroblasts have to do

A

needa navigate dense env. to get to wounds and heal them

173
Q

what is biggest issue when cell has to move thru dense env.

A

getting bulky nucleus thru tight spaces (don’t want it to rupture)

174
Q

in lab what is vimentin IF wrapped around

A

wraps around nucleus

175
Q

what is actomyosin machinery that generates majority of cellular forces is [ ] in

A

[ ] in cytoplasm, connects to IFs

176
Q

what is actomyosin contractility physically transmitted to

A

transmitted to IFs via plectin cross-links

177
Q

how do you get force from actomyosin contractility to intermediate filaments (vimentin IFs is the tow cable)

A

b/c they’re bound to plectin

178
Q

what do actomyosin and IFs together allow

A

solve problem of getting bulky nucleus thru tight spaces

179
Q

what do septins form

A

filaments, highly enriched under nucleus [influence microtubule & actin function, form filament, sheets, rings]

180
Q

what can septins form

A

diffusion barriers that divide cell

181
Q

what do plectins do

A

connect IFs to other cytoskeletal structures

bio 211 (18 decks)

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