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Cell Bio (BIOL 4004) > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

Actin filaments underlie the plasma membrane and provide…

A

strength and shape to the lipid bilayer

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2
Q

3 types of transient structures formed by actin

A
  1. lamellipodia & filopodia
  2. contractile ring
  3. growth cones
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3
Q

actin filaments form _ when stabalized by _

A

form stiff and relatively permanent structures when stabilized by actin binding proteins

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4
Q

_ increase the surface area of intenstinal epithelial cells

A

microvilli

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5
Q

actin filament subunits

describe structure

A

Globular actin (G-Actin) assemble head-to-tail to form protofilaments (F-actin) and F actin twist around each other to form actin filament

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6
Q

F-actin _ to form actin filaments

A

twist around each other in a right handed helix

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7
Q

each G actin has a _

A

binding site for ATP

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8
Q

actin filaments are similar to microtubles because they are

5 things

A
  1. found in all eukaryotes
  2. polar
  3. dynamic unless cap
  4. nucleation is rate limiting step
  5. filament grow more rapidly at plus end
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9
Q

barbed end is the _ while pointed is the _

A

plus end, minus end

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10
Q

latrunculin

A

binds actin monomers and
results in filament depolymerization

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11
Q

phalloidin

A

binds to and stabilizes actin filaments, causing a net increase in polymerization

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12
Q

Subunits bound to thymosin…

A

can’t add to either end of a filament, or hydrolyze/exchange their bound nucleotide

no addition to filament

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12
Q

Subunits bound to thymosin…

A

can’t add to either end of a filament, or hydrolyze/exchange their bound nucleotide

no addition to filament

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13
Q

profilin

A

Profilin binds to the end of a subunit which would normally add to the minus end of a filament, leaving exposed the site on the monomer that binds to the plus ends of filaments

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14
Q

Thymosin and profilin…

A

cannot bind to the same actin monomer at the same time

compete for binding

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15
Q

Activation of a small amount of profilin…

A

can produce rapid filament assembly
1. Profilin binds to monomers which are transiently released by thymosin
2. Profilin-bound monomers are then added to the plus ends of actin filaments
3. Once bound to a filament, the profilin is released and recycled for further rounds of filament elongation

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16
Q

two ways how profilin is regulated

A
  • profilin phosphorylation
  • profilin binding to inosol phospholipids
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17
Q

Arp 2/3 complex do what

A

nucleates the assembly of branched networks of actin filaments

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18
Q

Arp 2/3 steps

A
  1. in absense of activating factor, Arp 2 & 3 are held together by accessory proteins in a conformation that prevents nucleation
  2. activating factor binds to the complex & conformational change
  3. Arp2/3 nucleation by binding to minus end of the actin filament
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19
Q

Arp 2/3 complex is formed from

A

two actin related proteins (ARPs)

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20
Q

Arp 2/3 complex is most efficient at nucleating filament growth when ___ resulting in the formation of

A

it is attached to the side of a preexisting actin filament at a 70 angle,
branched actin networks

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21
Q

formins

do what

A

nucleate the growth of straight, unbranched filaments which can be crosslinked by accessory proteins
* each formin subunit binds one actin monomer
* as filament grows, formin remain on plus end
* remains attached even as new protofilaments are added

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22
Q

Nucleation of actin filaments often occus at _ resulting in _

A

occurs at or near the plasma membrane, resulting in a high density of actin filaments at the cell periphery.

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23
Q

cell cortex

A

actin rich region just benath the plasma membrane

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24
Q

microvilli and filopodia

A

spiky projections formed from parallel bundles of
actin filaments

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25
Q

lamellipodia

A

flat protrusive veils that help move cells over solid substrates

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26
Q

tropomyosin

A

a. Elongated protein which binds simultaneously to six or seven adjacent subunits
b. Prevents interaction of actin filament with other proteins (e.g. myosin motors)
c. Important component of muscle sarcomeres

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27
Q

capping proteins…

A

bind to the ends of actin filaments to slow the rate of filament growth and depolymerization

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28
Q

gelsolin…

A

severs actin filaments

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29
Q

after severing, gelsolin…

A

remains attached to the actin filament and caps the new plus ends

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30
Q

gelsolin is activated by

A

high levels of cytosolic Ca

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31
Q

gelosin proteins structure

A
  1. one domain that binds to an exposed region on filament
  2. second domain binds to a region that is normally hidden
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32
Q

how is it proposed that gelsolin molecules work

A

they bind to surface of a filament and wait until the hidden binding site is exposed because of a temp flunctuation
the insertation of second domail - breakage

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33
Q

cofilin _ by _

does what and how

A
  • destabilized actin filaments
  • it binds along the length of an actin filament and forces the filament to twist more tight
  • this weakens contacts between actin subunit and makes the filament brittle
  • severed ends undergo rapid deploymerization
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34
Q

cofilin preferentially binds _

A

ADP containing actin filaments, so older filaments

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35
Q

Bundling proteins

A

Proteins which cross-link unbranched actin filaments into parallel arrays

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36
Q

alpha actinin is a

A

bundling protein which produces loosely packed bundles of oppositely polarized actin filaments, leaving sufficient space for addition of myosin 2

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37
Q

alpha actinin are found in

A

stress fibers and contractile bundles

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38
Q

fimbrin

A

Bundling protein which promote the formation of tightly-packed, non-contractile actin filament bundles

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39
Q

fimbrin bundles _ myosin 2

A

exclude

tightly packed

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40
Q

Gel-like networks are formed from

A

branched filaments nucleated by Arp 2/3 complexes

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41
Q

gel forming proteins have

A

long, bent linkages between actin binding domains, resulting in formation of 3d actin gels

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42
Q

filamin

A

Gel-forming protein which cross-links actin filaments at right angles to promote the formation of web-like networks with the consistency of highly viscous gels; these proteins are necessary for the formation of the lamellipodia used by cells to crawl across a solid surface

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43
Q

filamin is necessary for

A

the formation of the lamellipodia used by cells to crawl across a solid surface

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44
Q

spectrin structure

A

long flexible composed of two alpha and two beta subunits with actin binding sites

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45
Q

spectrin forms

A

2d network under plasma membrane of red blood cells

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46
Q

spectrin molecules are held together by

A

a protein complex whhich includes short actin filaments

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47
Q

the heavy chains of myosin motors

A

contain globular head domains which control filament binding specificity, and hydrolyze ATP to provide the energy for movement.

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48
Q

c-termini of heavy chain of myosin

A
  • form long coiled tails
  • bind to cargo and other myosin heavy chains to make dimers
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49
Q

what allows mysosin to bind to other cargo

A

tail sequences being diverse

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50
Q

_ is very important to construction and function of stereocilia

A

myosin

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51
Q

mutations in myosin are known to cause

A

deafness

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52
Q

the motor activity of myosin is localized to

A

S1 fragment

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53
Q

S1 fragment

A

Myosin motor domains released by digestion of thick filaments with chymotrypsin and papain; motor activity is localized to this fragment

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54
Q

S1 fragment

A

Myosin motor domains released by digestion of thick filaments with chymotrypsin and papain; motor activity is localized to this fragment

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55
Q

how does myosin 2 move along actin

A
  1. first the myosin is in rigor (no nucleotide and head attached to filament)
  2. ATP binding = release of filament
  3. hydrolysis displaces the head, moves the lever arm forward
  4. head binds to new site, lever & head back to normal position, causes power stroke bc rest of myosin pulled forward
  5. back to rigor conformation
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56
Q

atp causes changes in _ in myosis

A

actin binding affinity

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57
Q

ATP binding causes myosin motor head to

A

release actin

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58
Q

myosin 2 functions in

A
  • cytokinesis
  • cell locomotion
  • muscle contraction
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59
Q

myosin 2 forms dimmers by

A

alpha helical tail domains of two heavy chains wrap around each other to form coiled tail of dimer

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60
Q

myosin two dimers form

A

striated muscle cells as bipolar thick filaments
* coiled coil bundle with other coils
* heads are oreintated opposite direction at the two ends

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61
Q

all the muscle types depend on

A

ATP driving sliding of arrays of actin filaments against arrays of myosin 2 filaments

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62
Q

all the muscle types depend on

A

ATP driving sliding of arrays of actin filaments against arrays of myosin 2 filaments

63
Q

skeletal muscle is in charge of

A

voluntary movement

64
Q

smooth muscle in charge of

A

involuntary contraction of gut walls

65
Q

skeletal muscles are formed by _ and consist of _

A

formed by fusion of myoblasts and cytoplasm is filled with myofibrils

66
Q

myofibrils are composed of

A

repeating contractile units called sarcomeres

67
Q

sarcomeres contain

general

A

overlapping arrays of thin (actin) and thick (myosin 2) filaments

68
Q

a bands of sarcomeres

A

span the length of the thick myosin filaments, contains overlapping thin filaments

69
Q

m lines of sarcomeres

A

link thick filaments into hexagonal lattices

70
Q

I band sarcomeres

A

the potions of thin filaments that do not overlap thin filaments

71
Q

z discs sarcomeres

A

cap plus ends and bundle thin filaments, boundry of sacromeres

72
Q

the uniformity and stability of sarcomeres is due to

general

A

accessory proteins

73
Q

_ stabalizes plus ends of thin falments in sarcomeres

74
Q

tropomodulin

A

stabilizes minus ends of thin filaments of sarcomere

75
Q

nebulin

A

determines length of thin filaments of sarcomere

76
Q

titan

A

positions thick filaments of sarcomere midway between z discs
* acts like a spring, unfolds when muscle is stretched

77
Q

thick filaments of sarcomeres are arranged in

A

a hexagonal latttice

78
Q

sarcomeres muscle contraction what happens and how

A
  • bipolar myosin thick filaments walk towards plus ends of sets of actin thin filaments with opposite polarity
  • thick and thin filaments slide past each other
  • sarcomeres shorten as the overlap of the thick and thin filaments increases
79
Q

t-tubules

A
  • folds of the plasma membrane that extend inwards and surround each myofibril
  • convey action potentials down into the cell
80
Q

sarcoplasmic reticulum

A

storage site for intracellular Ca in muscle cells
* surround myofibrils

81
Q

when t tubule is depolarized…

A
  • voltage gated Ca channels in t tubules open and CA in cell
  • This triggeres opening of Ca release channels in sarcoplasmic reticulum, more Ca in cytosol
  • contraction
  • transient increase: ATP dependent Ca pumps in SR membrane return Ca levels to normal
82
Q

tropomysin does what

A

prevents myosin from binding to thin filaments

83
Q

how does troponin complex work

A
  • in resting muscle, tropomyosin molecules bind alon actin filaments and mask myosin binding sites
  • when Ca cytosol up, troponin C binds Ca and troponin I release its hold on actin
  • tropomyosin shifts its position, causing myosin binding sites to be exposed
84
Q

regulation of smooth muscle contraction process

A
  • activation of cell surface receptors triffers release of Ca from sarcoplasmic reticulum
  • Ca binds to calmodulin
  • calmodulin binds to myosin light chain kinase (MLCK)
  • MLCK phsophorylates regulatory myosin light chain
  • smooth msucle contracts
85
Q

contraction causes smooth muscle cells to _ in length

86
Q

in non muscle contractile cells, myosin 2

A
  • present in inactive bent conformation
  • ATP phsophorylation by MLCK causes active state
  • activate state is extended and allows formation of bipolar myosin thick filaments
87
Q

filopodia are

structure

A

bundles of parallel actin filaments

88
Q

Lamellipodia are

structure

A

sheets of cross linked actin filaments

89
Q

invadopodia secret

A

matrix degrading proteases

90
Q

_ are used to study lemellipodia

A

keratocytes

91
Q

actin polymerization occurs at the

A

leading edge

92
Q

newly formed filaments at the leading edge contain mostly _ while the rear end contains _

A

ATP- actin, ADP-actin

93
Q

cofilin

A

preferentially binds to filaments containing ADP-actin, deplymerizing the actin filaments at the rear of the network

94
Q

what does actin networks rely on to move forward

A

treadmilling

95
Q

focal contacts serve as _, allowing

A

anchors for the leading edge, allowing the cell ot generate traction on the substratum and move forward

96
Q

focal adhesions are formed

A

between actin skeleton and components of the ECM

97
Q

activation of Cdc42

A

triggers actin polymerization and bundling to form filopodia

98
Q

activation of Rac

A

promotes actin polymerization at the cell periphery, leading to lamellipodia

99
Q

activation of Rho triggers

A

formation of stress fibers and the clustering of integrins and associated proteins to form adhesions

100
Q

how does Cdc42 work

A

Cdc42-GTP binds to open, active form of WASp, active WASp bind to Arp 2/3 and increase its nucleating activity

101
Q

Rac-GTP activates

A

WASp and PAK which leads to brached actin web in lamellipodia

102
Q

Rac-GTP inhibits

A

MLCK and MHC which causes less stress fiber formation

103
Q

PAK inhibits

A

MHC and MLCK which decreases myosin activity and less stress fiber formation

104
Q

Rho–GTP pathway

A
  • activates formins -> actin bundle growth
  • activates Rock which activates MLC(P) and LIM and inhibits MLC phosphatase
  • MLC(P) increases myosin activity
  • LIM inhibits cofilin
  • overall everything leads to more stress fibers and integrin clustering and focal adhesion formation
105
Q

binding of a chemoattractant leads to the

A

activation of Rac at the leading edge and Rho at the trailing edge

106
Q

Rho and Rac activation

A

inhibites each other

107
Q

Intermediate Filaments are most prominent

A

in cells subjected to mechanical stress

ropelike -> good for stretch but dont break

107
Q

Intermediate Filaments are most prominent

A

in cells subjected to mechanical stress

ropelike -> good for stretch but dont break

108
Q

IF main function is to

A

enable cells to withstand stretching

109
Q

IL monomers are

A

long fibrous proteins which form coiled coil dimers

110
Q

IF monomers are _

structure

A

alpha helical rods with heptad repeats

111
Q

why are coiled coils of IF so stable

A

monomers have 7 repeats in which first and fourth AA are nonpolar
* non polar stripes align and form hydrophobic interactions between two alpha helix monomers, polar side chains exposed

112
Q

soluable subunits of IF

A
  • tetramers
  • two dimers align side by side in an antiparllel straggered formation to form non po;ar tetramers
  • tetramers interaction end to end to form protofilament
113
Q

IFs are formed from

A

8 protofilaments packed together and twisted around each other

114
Q

cross sections of IFs contain

A

8 tratramers, 16 dimers and 32 alpha helices

115
Q

IF are non polarized bc

A

half of the dimers point in opposite directions

116
Q

strength of IFs comes from

A

lateral, hydrophobic interactions between protofilaments

117
Q

keratin filaments are bundles by proteins to form

A

apical layer of epidermis

118
Q

mutations in keratin cause

A

skin blistering diseases

119
Q

neurofilaments are a type of

120
Q

desmin is a type of

A

IF expressed in muscle cells

121
Q

desmin is a type of

A

IF expressed in muscle cells

122
Q

desmin forms

A

a scaffold around the Z disc of the sarcomere

123
Q

nuclear lamins

A

forms a 2d network which gives nucleus shape and stability

124
Q

nculear lamins provide

A

anchoring sites for chromatin and nuclear pores

125
Q

A-type lamins finction

A

as scaffolds for proteins that control transcription, chromatin organization and signal transduction

126
Q

laminopathies are associated with _ and are due to _

A

mutations in lamin A and may be due to weakening of the nuclear envelope

cause premature aging

127
Q

laminopathies are associated with _ and are due to _

A

mutations in lamin A and may be due to weakening of the nuclear envelope

cause premature aging

128
Q

plakins

A

link IF networks to the rest of the cytoskeleton

129
Q

SUN proteins bind

A

nuclear lamina or chromosomes

located in inner nuclear membrane

130
Q

located in outer nuclear membrane KASH proteins bind

A

actin filaments, microtubles and IFs

131
Q

in the perinuclear space,

A

SUN proteins bind to KASH proteins, thus linking the nucleus to the cytoskeleton

132
Q

cytoskeleton being linked ot nuclear interior is important for

A

movement of chromosomes

133
Q

during muscle contraction, the A band

A

styas constant

134
Q

during muscle contraction, the I band

A

moves towards the center of the sarcomere and increases its overlap and decreases in length

135
Q

during muscle contraction, the H band

A

H band becomes shorter in length as its overlap with other components increases.

136
Q

during muscle contraction, the Z discs

A

come closer together

137
Q

during muscle contraction, the M line

A

remains in the center

138
Q

during muscle contraction, the M line

A

remains in the center

139
Q

during muscle contraction, titan

A

is stretched

140
Q

Why is it important for Rac to be activated at the leading edge, and Rho at the trailing edge?

A
  • Rac responsible for protusion and attachement
  • Rac results in lamellipodia which importnat for protrusion
  • Rho required for traction because stress fiber formation
141
Q

Proteins which bind to actin subunits and prevent their incorporation into filaments.

142
Q

Membrane folds which convey electrical signals to the myofibrils of muscle cells.

143
Q

Membrane folds which convey electrical signals to the myofibrils of muscle cells.

144
Q

The cytoskeletal filament that is not polarized.

A

intermediate

145
Q

Gel-forming protein which cross-links actin filaments at right angles to promote the formation of web-like networks with the consistency of highly viscous gels.

146
Q

The class of intermediate filaments expressed in epithelial cells.

147
Q

Formins promote

A

the formation of unbranched actin filaments.

148
Q

Region of the sarcomere where the plus ends of thin filaments are capped by CapZ and bundled by α-actinin.

149
Q

Flat, sheet-like protrusions formed by actin networks at the leading edge of migrating cells.

A

lamellipodia

150
Q

Monomeric GTPase which promotes the formation of stress fibers via the activation of formin proteins and myosin-II filament assembly.

151
Q

chemotaxis

A

Movement of a cell in the direction of a diffusible chemical gradient.

152
Q

The _ surface of skin, known as the stratum corneum, is composed of the…

A

apical, remnants of dead skin cells and the network of filaggrin-bundled keratin filaments that were contained within those cells.

153
Q

S1 fragments are

A

myosin motor domains isolated by the enzymatic digestion of thick filaments.

Cell Bio (BIOL 4004) (8 decks)

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