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BIO107 - CELL AND MOLECULAR BIOLOGY > Cytoskeleton (1-3) > Flashcards

Cytoskeleton (1-3) Flashcards

1
Q

Families of protein filaments

A

-actin filaments
-microtubules
-intermediate filaments

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2
Q

for cells to function properly, they must organize themselves in space and interact mechanically with each other and with their environment.

A

cytoskeleton

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3
Q
A
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4
Q

shape of the cell’s surface; whole-cell locomotion; pinching of one cell into two.

A

Actin filaments

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5
Q

positions of membrane-enclosed organelles; direct intracellular transport; from the mitotic spindle.

A

Microtubules

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6
Q

mechanical strength

A

intermediate filaments

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7
Q

-are dynamic and adaptable
-can change or persist, according to need
-a structural rearrangement in a cell requires extra energy when conditions change.

A

Cytoskeletal systems

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8
Q

-underlie the plasma membrane of animal cells.
-strength and shape to its thin lipid bilayer.

A

Actin filaments

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9
Q

cell-surface projections

A

lamellipodia and filopodia

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10
Q

on the surface of hair cells in the inner ear contain stable bundles of actin filaments that tilt as rigid rods in response to sound.

A

stereocilia

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11
Q

on the surface of intestinal epithelial cells vastly increase the apical cell-surface area to enhance nutrient absorption.

A

microvilli

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12
Q

In plant, ____ filaments drive rapid streaming of the cytoplasm inside cells.

A

Actin

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13
Q

-found in cytoplasmic array that extends to cell periphery.
-form a bipolar mitotic spindle during cell division.

A

Microtubules

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14
Q

-function as motile whips or sensory devices on the surface of the cell.
-tightly aligned bundles that serve as tracks for the transport of materials down along neuronal axons.

A

cilia

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15
Q

In plant cells, organized arrays of _____ help to direct the pattern of cell wall synthesis.

A

microtubules

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16
Q

in many _______, microtubules form framework upon the entire cell is built.

A

protozoans

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17
Q

-line the inner face of the nuclear envelope, forming a protective cage for the cell’s DNA.

A

intermediate filaments

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18
Q

in the ________, intermediate filaments twisted into strong cables that can hold epithelial cells sheet together or help nerve cells to extend long and robust axons, and allow to form tough appendages such as hair and fingernails.

A

cytosol

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19
Q

rapid reorganization of cytoskeleton

A

cell division

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20
Q

After the chromosomes have replicated, the ________ _______ array that spreads throughout the cytoplasm is reconfigured into the bipolar _______ _______.

A

interphase microtubule, mitotic spindle

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21
Q

enable the fibroblast to crawl across the surface of the dish rearrange so that the cell stops moving and assume a more spherical shape.

A

specialized actin structures

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22
Q

after replication: form a belt around the middle of the cell

A

actin and motor protein

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23
Q

constricts like a tiny muscle to pinch the cell into two.

A

contractile ring

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24
Q

a protrusive structure filled with newly polymerized actin filaments

A

neutrophils

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25
Q

produce stable, large-scale structures for cellular organization.

A

mature neurons or epithelial cells

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26
Q

specialized epithelial cells in the intestines and lungs

A

microvilli and cilia

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27
Q

able to maintain a constant location, length, and diameter over the entire lifetime of the cell.

A

microvilli and cilia

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28
Q

for the actin bundles at the cores of microvilli on intestinal epithelial cells, is only a ____ days.

A

few

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29
Q

stereocilia on the hair cells

A

lifetime

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30
Q

Cytoskeleton is also responsible for large-scale ______ _____, enabling cells to tell the difference between top and bottom or front and back.

A

cellular polarity

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31
Q

use organized arrays of microtubules, actin filaments, and intermediate filaments to maintain the critical differences between the apical surface and the basolateral surface.

A

polarized epithelial cells

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32
Q

also must maintain strong adhesive contacts with one another to enable this single layer of cells to serve as an effective physical barrier.

A

polarized epithelial cells

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33
Q

How does cells builds filaments?

A

by assembling large numbers of the small subunits, like building a skyscraper out of bricks.

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34
Q

can diffuse rapidly in the cytosol, whereas the assembled filaments cannot.

A

small subunits

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35
Q

subunits for actin filaments

A

actin subunits

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36
Q

subunits for microtubules

A

tubulin

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37
Q

subunits of intermediate filaments

A

smaller subunits;
symmetrical

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38
Q

form as polymeric assemblies of subunits that self-associate, using a combination of end-to-end and side-to-side protein contacts.

A

the three major types of cytoskeletal filaments

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39
Q

The subunits of actin filaments and microtubules are asymmetrical and bind to one another head-to-tail so that they all point in one direction.

A

Polarity

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40
Q

-are symmetrical and thus do not form polarized filaments with two different ends.
-also do not catalyze the hydrolysis of ATP or GTP.

A

Intermediate filament subunits

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41
Q

Microtubules are built of ___ protofilaments

A

13

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42
Q

linear strings of subunits joined end-to-end that associate with one another laterally to form a _______ ________.

A

hollow cylinder

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43
Q

the greater energy required to break multiple noncovalent bonds simultaneously allows microtubules to resist ______ _______.

A

thermal breakage

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44
Q

-determines the spatial distribution and the dynamic behavior of the filaments.
- bind to the filaments or their subunits to determine the sites of assembly of new filaments.
- bring cytoskeletal structure under control of extracellular and intracellular signals.
- maintain a highly organized but flexible internal structure.

A

accessory proteins

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45
Q

among the most fascinating proteins that associate with the cytoskeleton are the ______ ________.

A

motor proteins

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46
Q

Where does the motor protein bind?

A

polarized cytoskeletal filament.

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47
Q

uses the energy derived from repeated cycle of ATP hydrolysis to move along the filament, and the “cargo” they carry

A

motor proteins

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48
Q

what many motor proteins carry

A

membrane-enclosed organelles

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49
Q

What are the organelles that the motor proteins carry?

A

mitochondria, Golgi stacks or secretory vesicles to their appropriate location in the cell.

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50
Q

Other motor proteins cause _____ ______ to exert tension or to slide against each other, generating the force that drives such phenomena as muscle contraction, ciliary beating, and cell division.

A

cytoskeletal filaments

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51
Q

Bacteria has ______ of all eukaryotic cytoskeletal filaments.

A

homologs

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52
Q

-tubulin homolog –>forms Z-ring (septum during cell division)
-generate a bending force that drives the membrane invagination and site for localization of enzymes.

A

FtsZ

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53
Q

-actin homolog
-scaffold to direct the synthesis of the peptidoglycan cell wall

A

MreB and Mbl

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54
Q

abnormalities in cell shape and defects in chromosomes segregation

A

mutations

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55
Q

bacterial actin homolog; encoded by a gene on certain bacterial plasmids that also carry genes responsible for antibiotic resistance.

A

ParM

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56
Q

ParM assembles into filaments that associate at each end with a copy of the plasmid, and growth of the ParM filament pushes the ______ ______ ______ apart

A

replicated plasmid copies

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57
Q

-influences the crescent shape of Caulobacter crescentus
-homolog of intermediate filaments

A

Crescentin

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58
Q

actin subunit

A

globular or G-actin

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59
Q

How many amino acid polypeptide carrying a tightly associated molecule of ATP or ADP does the actin subunit globular or G-actin have?

A

375

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60
Q

three isoforms of actin

A

alpha (a), beta (B) and gamma (y) actin

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61
Q

isoform of actin that is expressed in muscle cells

A

a-Actin

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62
Q

isoforms of actin that are found together in almost all non-muscle cells.

A

B- and y-Actin

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63
Q

Assembly of actin subunits

A

head-to-tail–> tight, right-handed helix

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64
Q

Actin subunits assemble head-to-tail to form a tight, right-handed helix, forming a structure about 8 nm wide called ______ or ________.

A

Filamentous or F-actin

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65
Q

filaments are polar and have structurally different ends: a slower growing minus end or _____ ___

A

pointed end

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66
Q

filaments are polar and have structurally different ends: a faster-growing plus end or ______ ___.

A

barbed end

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67
Q

nucleotide-binding cleft directed toward the ______ ___.

A

minus end

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68
Q

the minimum length at which random thermal fluctuations are likely to cause it to bend.

A

persistence length

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69
Q

The regulation of actin filament formation is an important mechanism by which cells control their _____ and _______.

A

shape and movement

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70
Q

subunits assemble into an initial aggregate, or nucleus, that is stabilized by multiple subunit-subunit contacts and can then elongate rapidly by addition of more subunits.

A

nucleation

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71
Q

is rate limiting and is additionally inhibited by actin-binding proteins

A

formation of small actin oligomers

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72
Q

In vitro polymerization of G-actin proceeds in three sequential phases, what are these?

A

-nucleation
-elongation
-steady-state

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73
Q

lag period; G-actin aggregates into short, unstable oligomers; when oligomers reaches a certain length, it can act as a stable seed or nucleus.

A

Nucleation

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74
Q

rapidly increases in length by the addition of actin monomers to both of its ends.

A

elongation

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75
Q

as F-actin filament grows, the concentration of G-actin monomers ______.

A

decreases

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76
Q

G-actin monomers exchange with subunits at the filament ends, but there is no net change in the total mass of filaments.

A

steady-state

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77
Q

when steady-state phase has been reached, the concentration of the pool of unassembled subunits is called ______ ______, __

A

critical concentration, Cc

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78
Q

the ratio of the “on” and “off” rate constant

A

dissociation constant

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79
Q

measures the concentration of G-actin where the addition of subunits is balanced by the dissociation of subunits

A

dissociation constant

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80
Q

actin filaments grow faster at ____ ___ than at _____ ___.

A

plus end, minus end

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81
Q

manifested by the different rates at which G-actin adds to the two ends

A

polarity of F-actin

82
Q

nucleate the polymerization of G-actin

A

myosin-decorated actin filaments

83
Q

newly polymerized (undecorated) actin is ______ times as long at the (+) end as at the (-) end of the filaments.

A

5-10

84
Q

difference in elongation rates at the opposite ends of an actin filament is caused by

A

a difference in Cc values at the two ends

85
Q

the plus end of an actin filament is ______, it can elongate only from its minus end

A

capped

86
Q

elongation takes place only at the plus end when the minus end of a filament is ______.

A

blocked

87
Q

Cc is about ____ _____ lower for polymerization at the (+) end than for addition at the (-) end

A

six times

88
Q

G-actin concentration below Cc+, there is __ ________ ______.

A

no filament growth

89
Q

G-actin concentrations between Cc+ and Cc-

A

growth is only at the (+) end

90
Q

G-actin concentration above

A

no growth at both ends

91
Q

G-actin concentrations intermediate between the Cc values for the plus end the minus ends, subunits continue to be added at the end and lost from the minus end

A

steady-state phase

92
Q

newly added subunits travelling through the filament, as if on a ______, until they reach the plus end, where they dissociate

A

treadmill

93
Q

effect on filaments: Latrunculin

A

depolymerizes

94
Q

effect on filaments: Cytochalasin B

A

Depolymerizes

95
Q

effect on filaments: Phalloidin

A

stabilizes

96
Q
A
97
Q

Chemical inhibitors of actin

A

-Latrunculin
-cytochalasin B
-Phalloidin

98
Q

chemical inhibitors of Microtubules

A

-Taxol (paclitaxel)
-Nocodazole
-Colchicine

99
Q

effect on filaments: Taxol

A

stabilizes

100
Q

effects on filaments: Nocodazole

A

Depolymerizes

101
Q

effects on filaments: Colchicine

A

depolymerizes

102
Q

Binds actin subunits

A

Latrunculin

103
Q

Caps filament plus ends

A

Cytochalasin B

104
Q

Binds along filaments

A

Phalloidin

105
Q

Binds along filaments: Microtubules

A

Taxol

106
Q

Binds tubulin subunits

A

Nocodazole

107
Q

Caps filament ends

A

Colchicine

108
Q

polymerization of actin is controlled by

A

its concentration, pH, and conc. of salts and ATP

109
Q

actin behavior is regulated by _________ ________ that bind actin monomers or filaments

A

accessory proteins

110
Q

a measure of how long an individual actin monomer spends in a filament as it treadmills.

A

filament half-life

111
Q

50% of the actin is in _____ and 50% is
soluble ____

A

filament
monomer

112
Q

cell contains proteins that bind to the actin
monomers and make polymerization much ___ ____

A

less favorable

113
Q

inhibition of actin polymerization;
they cannot associated with either the plus
or minus ends; neither hydrolyze nor
exchange their bound nucleotide

A

thymosin

114
Q

binds to the face of the actin
monomer opposite the ATP-binding cleft,
blocking the side of the monomer that would
normally associate with the filament minus
end, while leaving exposed the site on the
monomer that binds to the plus end

A

Profilin

115
Q

binds to the face of the actin
monomer opposite the ATP-binding cleft,
blocking the side of the monomer that would
normally associate with the filament minus end, while leaving exposed the site on the monomer that binds to the plus end

A

profilin

116
Q

prerequisite for cellular actin polymerization

A

filament nucleation

117
Q

bring several actin subunits together to form a seed

A

actin-nucleating proteins

118
Q

occurs primarily at the plasma membrane, and therefore the highest density of actin filaments in most cells is at the cell periphery within the cell cortex

A

Arp2/3 complex and formins

119
Q

actin-related proteins

A

Arp2/3 complex

120
Q

the complex can attach to the side of another actin filament while remaining bound to the minus end of the filament that it has nucleated

A

treelike web actin-nucleating factors

121
Q

dimeric proteins that nucleate
the growth of straight, unbranched
filaments that can be cross-linked by
other proteins to form parallel bundles

A

formins

122
Q

appears nucleate actin
filament polymerization by capturing
two monomers

A

formin dimers

123
Q

strongly enhanced by the
association of actin monomers with
profilin

A

Formin-dependent actin filament

124
Q

alter filament behavior
-bind along the side
-bind to the ends

A

actin filament-binding proteins

125
Q

side-binding proteins; elongated protein that binds simultaneously to six or seven adjacent actin subunits

A

tropomysin

126
Q

binds at the plus end; stabilizes an actin filament (inactive)

A

capping protein (capZ)

127
Q

capping long-lived actin
filaments in muscle; minus end-binding
* binds tightly to the minus ends that have
been coated and stabilized by
tropomyosin
* reduce their elongation and
depolymerization

A

tropomodulin

128
Q

coats the filament completely and present in high amounts

A

side-binding

129
Q

affect filament dynamics

A

end-binding

130
Q
  • proteins that break an actin filament into
    many smaller filaments; generating new
    filament ends
  • newly formed ends nucleate filament
    nucleation
  • promotes depolymerization of old filaments
A

severing proteins

131
Q

One class of actin severing proteins

A

gelsolin superfamily

132
Q

-activated by high levels of cytosolic Ca2+
-interacts with the side of the actin filament and contains subdomains that bind to two different sites

A

gelsolin superfamily

133
Q

two different sites of gelsolin

A

-one that is exposed on the surface of the filament
-one that is hidden between adjacent subunits

134
Q

a second actin filament-destabilizing proteins (severing proteins)

A

cofilin

135
Q

-also called actin-depolymeriziing factor
-binds along the length of the actin filament, forcing the filament to twist a little more tightly.

A

cofilin

136
Q

weakens the contacts between actin subunits in the filament, making the filament less stable and more easily severed by thermal motions, generating filament ends that undergo rapid disassembly.

A

Mechanical stress induced by cofilin

137
Q

Cofilin binds preferentially to ____ _________ actin filaments rather than to ATP-containing filaments.

A

ADP-containing

138
Q

actin filaments containing ATP are resistant to _________

A

depolymerization

139
Q

Cofilin tends to dismantle the ______ filaments in the cell.

A

older

140
Q

actin filament types of arrays

A

-dendritic networks
-bundles networks
-weblike (gel-like) networks

141
Q

Arp 2/3 complex

A

dendritic networks

142
Q

made of the long, straight filaments produced by formins

A

bundles networks

143
Q

not -well defined

A

weblike (gel-like) networks

144
Q

different actin networks depends on

A

specialized accessory proteins

145
Q

cross-link actin filaments into parallel arrays

A

bundling proteins

146
Q

hold two actin filaments together at a large angle to each other, forming a looser meshwork

A

gel-forming proteins

147
Q

enable stress fiber and other contractile arrays to contract

A

myosin II

148
Q

close packing of actin filaments; not contractile

A

fimbrin

149
Q

cross-links oppositely polarized actin filaments into loose bundle; allowing the binding of myosin and formation of contractile actin bundles

A

a-actinin

150
Q

formation of a loose and highly viscous gel; by clamping together two actin filaments roughly at right angles

A

filamin

151
Q

defect in nerve-cell migration during early embryonic development

A

filamin A gene mutations

152
Q

periventricular region of the brain fail to migrate to the cortex and instead form nodules

A

periventricular heterotopia

153
Q

web-forming; long, flexible protein made out of four elongated polypeptide chains

A

spectrin

154
Q

concentrated beneath plasma membrane; forms a two-dimensional weblike network

A

spectrin in RBCs

155
Q

strong, yet flexible ____ ___ that provides mechanical support allow RBC to spring back its shape

A

cell cortex

156
Q

it can form contractile structures through the action of myosin motor proteins

A

Myosin and Actin

157
Q

-first motor protein identified
-generates force for muscle contraction

A

skeletal muscle myosin

158
Q

an elongated protein formed from two heavy chains and two copies of each light chains

A

myosin II

159
Q

globular head domain at its N-terminus. contains force-generating machine

A

heavy chain

160
Q

amino acid sequence forming an extended coiled-coil

A

mediates heavy-chain dimerization

161
Q

bind close to N-terminal head

A

light chains

162
Q

oriented in opposite directions

A

myosin heads

163
Q

-binds and hydrolyzes ATP
-use the energy of the ATP hydrolysis to walk toward the plus end of an actin filament

A

myosin head

164
Q

result in powerful contraction

A

ATP-driven sliding of actin filaments

165
Q

use structural changes in their ATP-binding sites to produce cyclic interactions with a cytoskeletal filament

A

motor proteins

166
Q

propels them forward in a single direction to a new binding site along the filament

A

ATP binding, hydrolysis, and release

167
Q

each step of the movement along actin is generated by the swinging of an 8.5 nm-long a helix

A

lever arm

168
Q

a pistonlike helix that connects movement at the ATP-binding cleft in the head to small rotations

A

converter domain

169
Q

sliding of myosin II along actin filament

A

muscle contraction

170
Q

bulk of the cytoplasm inside is made up of ______

A

myofibrils

171
Q

a cylindrical structure 1-2 um in diameter that is often as long as the muscle cell itself. It consists of a long, repeated chain of tiny contractile units

A

myofibril

172
Q

-a long, repeated chain of tiny contractile units
-give the vertebrate myofibril its striated appearance
-parallel and partly overlapping thin and thick filaments

A

sarcomeres

173
Q

actin and associated proteins; attached at their plus ends to a Z disc; minus ends overlapped with the thick filaments

A

thin filaments

174
Q

hexagonal lattice, with actin filaments evenly spaced between the myosin filaments

A

thick filaments

175
Q

caused by the myosin filaments sliding past the actin thin filaments, with no change in the length of either type of filament

A

sarcomere shortening

176
Q

rise in cytosolic Ca2+ concentration initiates?

A

muscle contraction

177
Q

two major features of the muscle cell

A
  1. myosin motor heads coupled binding and hydrolysis to ATP
  2. a specialized membrane system relays the incoming signal rapidly throughout the entire cell
178
Q

signal from the nerves triggers an action potential

A

sarcoplasmic reticulum

179
Q

triggers the opening of Ca2+ release channels in the sarcoplasmic reticulum

A

Ca2+ influx

180
Q

elongated protein that binds along the groove of the actin filament helix

A

tropomysin

181
Q

complex of polypeptide (T, I, & C)

A

troponin

182
Q

pulls the tropomysin out of its normal binding groove that interferes with the binding of myosin head

A

troponin I-T complex

183
Q

binds up to four molecules of Ca2+, causes troponin I to release its hold on actin

A

rise in Ca2+, troponin C

184
Q

contraction is triggered by an influx of calcium ions, but different regulatory mechanism

A

in smooth muscle cells

185
Q

elevated intracellular Ca2+ levels regulate contraction by a mechanism that depends on ________

A

calmodulin

186
Q

Ca2+ bound calmodulin activates ____________, thereby inducing the phosphorylation of smooth muscle myosin on one of its two light chains

A

myosin light-chain kinase (MLCK)

187
Q

phosphorylated light chains

A

contraction

188
Q

dephosphorylated

A

inactive

189
Q

most heavily worked muscle

A

heart

190
Q

common cause of sudden death in young athletes

A

familial hypertrophic cardiomyopathy

191
Q

genetically dominant inherited condition

A

-heart enlargement
-abnormal small coronary vessels
-disturbances in heart rhythm

192
Q

encoding cardiac b myosin heavy chain or mutations in other genes encoding contractile proteins

A

point mutation in the genes

193
Q

minor missense mutations in the cardiac actin gene

A

dilated cardiomyopathy

194
Q

contain small amounts of contractile actin-myosin II bundles

A

non-muscle cells

195
Q

-found in Acanthamoeba castellani
-intracellular organization - microvilli and endocytosis

A

myosin I

196
Q

one-headed or two-headed

A

myosin family

197
Q

how many distinct myosin families?

A

37

198
Q

human genome includes ___ myosin genes

A

40

199
Q

two-headed myosin with a large step size; organelle transport along actin filaments; move processively along actin filaments without letting go.

A

myosin V

200
Q

actin cables in the mother cell point toward the bud, where actin is found in patches that concentrate where cell wall growth is taking place.

A

Saccharomyces cerevisiae

BIO107 - CELL AND MOLECULAR BIOLOGY (16 decks)

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