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BIOL 3302 > exam 4 > Flashcards

exam 4 Flashcards

1
Q

what is actin structurally similar to?

A

MreB

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2
Q

actin filaments are the subunit of what?

A

microfilaments

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3
Q

what is the subunit of microtubules?

A

alpha-beta tubulin dimer

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4
Q

of the three cytoskeleton filaments which is the thinnest and thickest?

A

thinnest: microfilaments (7-9 nm)
thickest: microtubules (25 nm)

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5
Q

why are vesicles not lost in the cytoskeleton as they move to their target?

A

due to the pathway already established by microfilaments and microtubules guiding vesicles from location to location

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6
Q

why do certain cells keep their structural integrity?

A

membrane is very thin, cytoskeletal elements provide a framework for the cell from the inside

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7
Q

in what way do G actin subunits come to form polarized F actin filaments?

A

in a reverse assemble

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8
Q

what is the composition of an F actin filament?

A

it is composed of two proto filaments

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9
Q

where is the actin nucleotide binding site located?

A

on the negative end of each proto filament

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10
Q

which end is the growing end on a F actin filament?

A

the positive end

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11
Q

compare and contrast where the majority of microfilaments might be located on an epithelial vs migrating cell

A

epithelial: at the apical surface
migrating: at the filopodium

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12
Q

present on the positive end, the ATP binding cleft on every actin is oriented toward the same end of the filament (T/F)

A

FALSE, the ATP binding site is on the negative end not positive

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13
Q

if we ran an actin experiment on top of a nucleotide such as ATP, what else would we need?

A

ions such as Mg2+, K+, Na+

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14
Q

how long will one single turn for an F actin microfilament be?

A

36 nm

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15
Q

what purpose does magnesium serve in the polymerization of G actin subunits?

A

it serves as a catalyst

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16
Q

what is nucleation?

A

the formation of an actin nucleus by 3 G actin monomers

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17
Q

during the 3 phases of in vitro G-actin polymerization what do we want to happen?

A

nucleation, we want to start the process of creating a microfilament structure

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18
Q

the nucleation phase is concurrent with what?

A

the lag phase, the nucleation phase is thermodynamically unfavorable and thus occurs gradually

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19
Q

decreasing the amount of G actin will eliminate the nucleation phase and allow for faster entry into elongation (T/F)

A

FALSE, less G actin concentration will decrease nucleation but will NOT allow for shortcut to elongation. this could only happen if we have an initial addition of actin filament/nuclei/seeds

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20
Q

only in the steady state do we have

A

10x speed on the positive end and the treadmill dynamic

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21
Q

what is the steady state necessary for?

A

to help maintain a certain level of length for optimal activity

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22
Q

elongation phase differs from steady state in that elongation allows for rapid assembly on each end of the filament (T/F)

A

TRUE, steady state has rapid assembly only on + end compared to - end but elongation phase grows from both ends

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23
Q

what is critical concentration?

A

the concentration necessary for polymerization

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24
Q

an actin concentration below the Cc would still result in a slight polymerization (T/F)

A

FALSE, Cc is all or nothing, we either reach it and polymerize or we don’t

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25
Q

how are steady state and Cc related?

A

both have filament assembly as a result of G actin addition and G actin disassembly being balanced

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26
Q

the equation for mass is?

A

total actin concentration - Cc

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27
Q

what is the Cc on the + end of F actin during actin treadmilling?

A

0.12 uM

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28
Q

how do we get the value for the + end of F actin during actin treadmilling?

A

rate of disassembly/rate of assembly (1.4/12)

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29
Q

what is the Cc of the - end of F actin during actin treadmilling?

A

0.6 uM

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30
Q

ratio for Cc on - end of F actin?

A

0.8/1.3

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31
Q

as a result of the steady state ratio of assembly and disassembly, what type of regions come about?

A

short region of ATP-actin and regions of ADP-Pi-actin toward the + end and ADP-actin toward the - end

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32
Q

treadmilling cannot do work in vivo (T/F)

A

FALSE, it can do work in vivo

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33
Q

what are the 3 actin binding proteins?

A

cyclin 1 profilin
cyclin 2 cofilin
cyclin 3 thymosin beta 4

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34
Q

compare and contrast cofilin and profilin

A

both: initially bind to an ADP-G actin
profilin: binds to sterically block ATP-G actin assembly at the - end
cofilin: binds 2-ADP-G actin monomers to induce a twist

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35
Q

which actin binding protein will enhance overall depolymerization?

A

cofilin because it twists off chunks of the F actin filament and creates new negative ends

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36
Q

how does the cell overcome excess ATP-G actin when there is no longer a need for elongation?

A

the thymosin beta 4 cycle buffers ATP-G actin by sequestering it during high concentration and releasing it in low concentration

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37
Q

what is the purpose of capping proteins?

A

they block assembly and disassembly at filament ends

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38
Q

+ capping proteins like CapZ and Gelsolin act on the + end of the growing filament to limit growth there in their own unique way (T/F)

A

TRUE

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39
Q

+ capping proteins CapZ and Gelsolin are under the control of PI(4,5)P2

A

FALSE, Gelsolin is under control of Ca+ concentration

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40
Q

what is the purpose of Gelsolin activity?

A

helps regulate actin that has grown past optimal limit

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41
Q

what does tropomodulin bind to?

A

binds to the - end of actin filament and tropomyosin

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42
Q

what is unique about tropomodulin capping?

A

stabilizes the filament

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43
Q

Arp2/3 helps in long filament formation

A

FALSE, formin helps in long filament formation

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44
Q

unlike Arp2/3, formin has multiple subunits

A

TRUE, there is the FH1, FH2, and RBD subunits and domains

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45
Q

what is unique about the nucleation that takes place with formin when compared to G actin?

A

G actin nucleation involves 3 subunits while formin nucleation by FH2 requires 2

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46
Q

what does FH2 bind to?

A

profilin-ATP-G actin

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47
Q

what amino acid is FH1 rich in?

A

it is proline rich

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48
Q

what is the purpose of FH1?

A

it acts as a landing site for profilin-ATP-G actin

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49
Q

CapZ binding will bind to the positive end of the filament and stop growing only after nucleation has started (T/F)

A

FALSE, CapZ can only affect FH2 domain before nucleation has occurred

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50
Q

what causes a formin protein to enter the active state?

A

an active RHO GTP will cause RBD to bind and activate the formin

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51
Q

what would happen if a mutation disables RHO?

A

RHO would be in a permanent inactive state and thus never allow for RBD binding. this would prevent activation of formin and reduce long filament formation

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52
Q

what would happen in a RBD mutation?

A

will prevent activation of formin

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53
Q

what would happen in a FH1 mutation?

A

decrease in profilin-ATP-G actin availability for FH2

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54
Q

what would happen if the FH1 amino acid (proline) was switched?

A

this will change the FH1 domain and prevent its function

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55
Q

what would happen in a FH2 mutation?

A

nucleation will be prevented and not protect against CapZ protein if a filament does end up forming. overall filament formation would be prevented.

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56
Q

what would happen in a profilin mutation?

A

this will not allow for essential subunits to be present for actin formation as ATP exchange is necessary

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57
Q

how are ATP G actin subunits transferred to the Arp2/3?

A

via the use of NPF

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58
Q

during branch assembly where are the ATP binding sites?

A

on the Arp2/3

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59
Q

what are the subunits of NPF?

A

W: Wh2
C: connector
A: acidic

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60
Q

what side of a ATP G actin binds to the Wh2 domain of NPF?

A

+ end

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61
Q

after binding a ATP-G actin on its + smooth head on the WH2 domain, the NPF will go on to bind the + end of existing actins to initiate branch growth

A

FALSE, once NPF binds atp G actin it will go to bind itself to the - end of an existing actin

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62
Q

NPF uses the connector domain to bind to the Arp2/3 complex

A

FALSE, the acidic domain does this

63
Q

what fungal alkaloid plays a similar role to CapZ?

A

cytochalsin D

64
Q

what does the sponge toxin latrunculin do?

A

it binds and sequesters G actin monomers

65
Q

what toxin will enhance nucleation by binding and stabilizing actin dimers?

A

jasplakinolide

66
Q

CDC25 and Rho are different classes of proteins

A

FALSE, both are membrane-bound G proteins

67
Q

what domain of the Wasp protein is regulated by PI(4,5)P2?

A

the basic domain B

68
Q

how does actin attach end to end to mebranes?

A

laterally

69
Q

what is Wiskott-Aldrich syndome?

A

a skin condition resulting in a low platelet count, immune deficiencies and Eczema

70
Q

where are fimbrin proteins located?

A

in the microvilli, filopodia, and focal adhesions

71
Q

what is the diff b/w fimbrin and alpha-actinin?

A

fimbrin has (N) actin filament binding domain and alpha-actinin has a Ca2+ binding domain

72
Q

what cross-linking protein is responsible for muscular dystrophy?

A

dystrophin

73
Q

what is unique of the filamin corss-linking?

A

creates a loss of 3D network with gel-like properties

74
Q

what cross-linking protein is responsible for providing spoke and hub structure?

A

spectrin

75
Q

dystrophin is important for linking what?

A

membrane protein to actin cortex in muscles

76
Q

what is unique of the dystrophin terminus?

A

it has a C terminus

77
Q

what cross-linking protein is typical of stress fibers and the muscle Z line?

A

alpha actinin

78
Q

how do we keep the structural integrity of multiple actin that are side by side?

A

via actin cross-linking proteins such as fimbrin which has N actin filament binding domain

79
Q

what is unique about the spacer sequences in spectrin?

A

they have an alpha and a beta

80
Q

myosin specificity comes from their different heads while the tail domain is preserved (T/F)

A

FALSE, there is a common head and specific tail

81
Q

how many peptides are in the head complex of myosin 2?

A

6 peptides

82
Q

how are the 6 peptides on the head complex divided?

A

2 heavy chains and 2 pairs of light chains (2 regulatory and 2 essential)

83
Q

where does chymotrypsin cleave?

A

near the end of the heavy chain and by the regulatory light chain

84
Q

what are the products of chymotrypsin?

A

a heavy meromyosin and light meromyosin

85
Q

papain cleavage cuts directly at the regulatory light chain and heavy chain intersection creating a HMM and LMM product (T/F)

A

FALSE, it creates a S1 and S2 product

86
Q

rank the myosin classes from largest step size to smallest

A

V (36nm), I (10-14nm), II (8nm)

87
Q

what myosin class is responsible for organelle transport?

A

myosin V

88
Q

the most common myosin class is ___________ responsible for _____________

A

myosin II, contraction

89
Q

class I myosin is responsible for membrane association and exocytosis

A

FALSE, endocytosis

90
Q

what is unique about myosin VI (6)?

A

it is the only myosin with a - end directed motor

91
Q

what happens when ATP is bound to myosin?

A

a conformational change occurs releasing S1 head from actin

92
Q

cocked stage is achieved by

A

hydrolysis of ATP into ADP + Pi

93
Q

only in the cocked state will the myosin head perform a power stroke

A

FALSE, power stroke is accomplished by Pi release once cocked myosin attaches to actin

94
Q

what causes rigor mortis?

A

a lack of ATP allowing for temporary binding. similarly, death prevents cell from pushing out calcium forcing muscles to contract

95
Q

what is defined as a sarcomere unit?

A

Z disk to Z disk

96
Q

why are Z disks important?

A

they establish the ideal amount of actin needed for a muscle and will cap this length

97
Q

in addition to its regulation of gelsolin, magnesium plays a role in the contraction of myosin head as the walk towards the + end during high concentration (T/F)?

A

FALSE, calcium ions play a role in muscle contraction

98
Q

sarcomere hold myosin actin filaments since they are the largest subunit of a muscle (T/F)

A

FALSE, sarcomere is the smallest subunit

99
Q

how does the body prevent excessive overstretching?

A

via titin connection between Z disk and M band

100
Q

nebulin will perform a similar role to titin in that it binds to actin to prevent excessive overstretching (t/f)

A

FALSE, nebulin binds to actin to determine optimal length

101
Q

resting muscle calcium concentration?

A

< 10e-7 M

102
Q

contracting muscle calcium concentration?

A

> 10e-6 M

103
Q

the sarcoplasmic reticulum plays a role in thin and thick filament calcium dependent regulatory mechanisms via its release of cytosol/sacroplasm calcium (t/f)

A

FALSE, only the thin filament is subject to this

104
Q

how do we propagate a nerve impulse signal from the neuromuscular junction throughout the muscle?

A

signal is propagated via transverse tubules across the sarcolemma

105
Q

the MLCK phosphorylates the essential light chains of the myosin to activate it (t/f)

A

FALSE, it phosphorylates the regulatory light chain

106
Q

how is myosin kept inactive during low concentration levels?

A

via the MLCP

107
Q

describe a calcium-independent mechanism that will activate myosin

A

Rho kinase will activate myosin 2 by inhibiting MLCP

108
Q

how does class 5 play a role with budding yeast?

A

it aids in cargo movement or organelles and higher components from mother cell to budding child

109
Q

what role does myosin II play in the nucleus?

A

it helps bind the ends of cytoplasmic microtubules to orient the nucleus in preparation for mitosis

110
Q

what are the characteristics of folded state of myosin V?

A

without cargo to bind the tails of myosin V, it will bind to each other and inactivate the motor head domain

111
Q

what is the lamelipodium?

A

a cytoskeleton protein actin projection that generates force for advancement of leading edge

112
Q

how does the lamellipodium extend?

A

via an Arp2/3 dependent mechanism

113
Q

what mediates the connection between actin filaments and ECM proteins?

A

integrin

114
Q

where does the actin-myosin II dependent contractions occur in the cell?

A

at the rear of the cell

115
Q

in order to continue moving the cell will have to recycle integrins at the rear via an exocytic cycle that will transport them to the front (T/F)

A

FALSE, it is an endocytic cycle

116
Q

branching filament create a connective net-like structure that allows for a high amount of contractile force to be withstood thus create stress fibers (t/f)

A

FALSE, stress fibers are created from long filaments

117
Q

stress fibers make up the content of the leading edge and advance cells moving forward (t/f)

A

FALSE, the leading edge is made up of branched Arp2/3 complex

118
Q

due to their vital role in activating both long and branched filament complexes, Rho family of GTPase are always found in the plasma membrane (t/f)

A

FALSE, the Rho family are known as peripheral membrane proteins and are kept inactive and away from the membrane until a signal reaches a receptor calling them to action

119
Q

Rho proteins are kept inactive via GAP (t/f)

A

FALSE, GAP makes RHO inactive but is kept inactive by GDI

120
Q

GEF activation of Rho will uncover what?

A

uncover membrane binding domain allowing for its attachment to the plasma membrane

121
Q

GEF will hydrolyze GTP onto Rho (t/f)

A

FALSE, GAP hydrolyzes but GEF only performs the exchange from GDP to GTP

122
Q

WASp and WAVE are both what?

A

NPF

123
Q

Cdc45 is a unique Rho GTPase in that

A

it has dual action of activating Arp2/3 branched filament formation (with WASp) and Par6 polarizing properties

124
Q

Cdc and Rac use NPF to activate Arp2/3 complex to create filopodia (t/f)

A

FALSE, Rac creates lamellipodia

125
Q

how is Rho-GTP activated?

A

activation by Rac GTP and LPA signal molecule

126
Q

filopodia and lamellipodium formation are independent (t/f)

A

FALSE

127
Q

why does active Rho inhibit Rac activation?

A

to ensure no leading edge structures form at the rear of the cell

128
Q

what mutation indicates a peripheral membrane ruffle formation?

A

a dominate-active Rac

129
Q

what mutation does a dominant active Cdc42 result in?

A

a spiky membrane due to abundant filopodia

130
Q

what mutation does a dominant active Rho cause?

A

formation of abundant stress fibers

131
Q

assembled tubulin hydrolyzes ______

A

GTP

132
Q

what is unique about the assembly of alpha beta tubulin?

A

it is dynamically unstable and polarized

133
Q

all microtubules nucleated from MTOC remain anchored at the + end (t/f)

A

FALSE, they remain anchored by the - ends

134
Q

all cytoskeletal subunits are highly polarized (t/f)

A

FALSE, intermediate filaments are unpolarized

135
Q

what is the difference between alpha and beta tubulin?

A

alpha is stuck with GTP and nonhydrolyzable/non-exchangeable. beta has a nucleotide binding region that is hydrolysable and exchangeable so it can house GDP or GTP

136
Q

calcium increases the affinity of the beta subunit for GTP with respect to GDP (t/f)

A

FALSE, it is magnesium

137
Q

describe the arrangement of protofilaments

A

they are staggered to ensure alpha tubulin units are contacted with neighboring alpha tubulin except at the seam where alpha is attached to beta

138
Q

the cytoplasm has a doublet protofilament structure (t/f)

A

FALSE, it has a singlet structure

139
Q

where would you find a double protofilament structure?

A

in cilia and flagella

140
Q

the centrioles and basal bodies have what kind of protofilament structure?

A

triplet

141
Q

microtubule assembly is dynamically unstable but why?

A

the dynamic instability depends on the presence or absence of GTP beta tubulin cap

142
Q

compare and contrast rescue and catastrophe GTP beta tubulin

A

rescue: GTP tubulin addition is greater than rate of GTP hydrolysis
catastrophe: rate of GTP hydrolysis is greater than rate of GTP tubulin addition

143
Q

where is the microtubule built up from?

A

from the gamma tubulin ring complex

144
Q

what are the 3 roles of MAP?

A
  • stability at C term
  • polymerization
  • gap between microtubules
145
Q

_______________ MAP causes instability

A

phosphorylated

146
Q

what is a contributing factor to Alzheimer’s?

A

Tau aggregation due to hyperphosphorylation

147
Q

kinesin 13 only binds to the + end (t/f)

A

FALSE, it prefers to bind to the + end but it will also bind to the -

148
Q

which disassembly protein binds to curved positions of the proto filament?

A

Op13/stathmin

149
Q

Op18/stathmin removes a dimer just like kinase 13 (t/f)

A

FALSE, it removes a pair of dimers

150
Q

which kinesins perform a walking motion?

A

kinesins 1 and 2

151
Q

what happens if dynamitin is overexpressed?

A

explosion of cell

152
Q

what would a defective kinesin 2 result in?

A

accumulation of particles in the - end

153
Q

when might tubulin and kinesin 13 be present?

A

during mitosis

154
Q

mitosis has microtubule instability due to what?

A

inhibition of XMAP2

BIOL 3302 (5 decks)

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