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Cell and Molecular Biology > Module 6: The Cytoskeleton (Function and Origin of Cytoskeleton, Actin and Actin-binding Proteins) > Flashcards

Module 6: The Cytoskeleton (Function and Origin of Cytoskeleton, Actin and Actin-binding Proteins) Flashcards

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1
Q

It allows cells to organize themselves in space, interact mechanically with each other, and engage with their environment.

A

cytoskeleton

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2
Q

What are the main families of protein filaments in the cytoskeleton? (3)

A
  • Actin filaments
  • Microtubules
  • Intermediate filaments
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3
Q

shape the cell’s surface, enable whole-cell locomotion, and assist in the pinching of one cell into two during division.

a family of protein filaments in the cytoskeleton

A

actin filaments

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4
Q

determine the positions of membrane-enclosed organelles, direct intracellular transport, and form the mitotic spindle.

a family of protein filaments in the cytoskeleton

A

microtubules

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5
Q

provide mechanical strength to the cell.

a family of protein filaments in the cytoskeleton

A

intermediate filaments

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6
Q

are dynamic and adaptable, allowing them to change or persist according to the cell’s needs.

A

Cytoskeletal systems

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7
Q

In a cell, this can occur with little extra energy when conditions change.

A

Structural rearrangements

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8
Q

Where are actin filaments located in animal cells?

A

plasma membrane

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9
Q

actin filaments provide __ and __ to the thin lipid bilayer of the plasma membrane.

A
  • strength
  • shape
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10
Q

What are the cell-surface projections formed by actin filaments? (2)

A
  • lamellipodia (sheet-like projection)
  • filopodia (spike-like projection)
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11
Q

Name two structures that are supported by actin filaments. (2)

A
  • Stereocilia
  • microvilli
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12
Q

found in a cytoplasmic array that extends to the cell periphery.

a family of protein filaments in the cytoskeleton

A

microtubules

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13
Q

They form a bipolar mitotic spindle during cell division.

a family of protein filaments in the cytoskeleton

A

microtubules

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14
Q

motile structures that function as whips or sensory devices.

A

cilia

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15
Q

Microtubules form tightly aligned bundles that serve as tracks for the transport of materials along __.

A

neuronal axons

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16
Q

In plants, microtubules help to direct the pattern of __.

A

cell wall synthesis

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17
Q

In protozoans, microtubules form a __ upon which the entire cell is built.

A

framework

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18
Q
  • line the inner face of the nuclear envelope.
  • They act as a protective cage for the cell’s DNA.

a family of protein filaments in the cytoskeleton

A

intermediate filaments

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19
Q

In the cytosol, intermediate filaments twist into strong cables that help hold __ together.

A

epithelial cell sheets

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20
Q

help nerve cells extend long and robust axons.

a family of protein filaments in the cytoskeleton

A

Intermediate filaments

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21
Q

Intermediate filaments form __ such as hair and fingernails.

A

tough appendages

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22
Q

The role of cytoskeleton essential for cell division.

A

rapid reorganization

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23
Q

Give an example of a cell type that undergoes rapid cytoskeletal reorganization.

A

Fibroblast

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24
Q

What structure do interphase microtubules form during cell division?

A

bipolar mitotic spindle

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25
Q

crawl across the surface of the dish

A

actin

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26
Q

It forms a belt around the middle of the cell to pinch it into two.

A

contractile ring

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27
Q

A cell that has protrusive structures filled with newly polymerized actin filaments

A

neutrophils

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28
Q

What characterizes stable, differentiated morphology in cells?

A

stable, large-scale structures

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29
Q

What are two examples of specialized epithelial cells that have distinct structures?

A
  • Microvilli in the intestines
  • cilia in the lungs
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30
Q

They maintain a constant location, length, and diameter over their entire lifetime.

A

specialized epithelial cells

Microvilli in the intestines; cilia in the lungs

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31
Q

How long do microvilli on intestinal epithelial cells typically last?

A

a few days

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32
Q

What is the lifespan of stereocilia on hair cells?

A

lifetime of the cell

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33
Q

How do these stable structures enable cells to perceive their orientation?

A

allow cells to differentiate between top and bottom, or front and back.

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34
Q

responsible for establishing large-scale cellular polarity, allowing cells to differentiate between top and bottom, or front and back.

A

cytoskeleton

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35
Q
  • have an apical surface and a basolateral surface.
  • maintain strong adhesive contacts with one another, enabling the single layer of cells to function as an effective physical barrier.
A

Polarized epithelial cells

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36
Q

A cell builds __ by assembling large numbers of small subunits.

A

filaments

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37
Q

The filament subunits diffuse rapidly in the cytosol, allowing for __.

A

rapid structural reorganizations

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38
Q

What are the subunits of actin filaments and what energy source do they utilize? (2)

A
  • actin subunits
  • ATP hydrolysis
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39
Q

What are the subunits of microtubules and what energy source do they utilize? (2)

A
  • tubulin subunits
  • GTP hydrolysis
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40
Q

A subunit that is smaller and symmetrical, forming helical assemblies

A

intermediate filament subunit

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41
Q

have asymmetrical subunits (head-to-tail orientation) that create polarity (2)

A
  • actin filaments (actin subunits)
  • microtubules (tubulin subunits)
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42
Q

A subunit that is symmetrical, meaning they do not have polarity and do not catalyze the hydrolysis of nucleotides.

A

intermediate filament subunit

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43
Q

built of 13 protofilaments, which are linear strings of subunits joined end-to-end that associate laterally to form a hollow cylinder.

a family of protein filaments in cytoskeleton

A

microtubules

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44
Q
  • The greater energy required to break multiple noncovalent bonds simultaneously allows microtubules to resist .
  • The structure allows for rapid subunit __ and loss at the __.
A

thermal breakage
* addition
* filament ends

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45
Q

Proteins which determine the spatial distribution and dynamic behavior of the filaments by binding to the filaments or their subunits to regulate the sites of new filament assembly.

A

Accessory proteins

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46
Q

Proteins which bring cytoskeletal structures under the control of extracellular and intracellular signals, maintaining a highly organized yet flexible internal structure.

A

Accessory proteins

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47
Q

Proteins which bind to polarized cytoskeletal filaments, use ATP hydrolysis for movement along the filaments, and transport “cargo” such as membrane-enclosed organelles.

A

Motor proteins

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48
Q

Proteins which cause cytoskeletal filaments to exert tension or slide against each other.

A

Motor proteins

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49
Q

Bacteria have __ of all eukaryotic cytoskeletal filaments.

A

homologs

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50
Q

A tubulin homolog in bacteria that forms the Z-ring, which contributes to septum formation during cell division and generates a bending force for membrane invagination.

A

FtsZ

“filamentous temperature-sensitive”

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51
Q

Serves as a site for the localization of enzymes and generates a bending force to drive membrane invagination during cell division.

A

Z-string

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52
Q

Actin homologs that provide a scaffold to direct the synthesis of the peptidoglycan cell wall. (2)

A
  • MreB
  • Mbl
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53
Q

What happens when mutations occur in MreB and Mbl? (2)

A
  • abnormalities in cell shape
  • defects in chromosome segregation
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54
Q

a 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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55
Q

ParM assembles into __ that associate at each end with a copy of the __, and the growth of the __ pushes the replicated __ copies apart.

A
  • filaments
  • plasmid
  • ParM filament
  • plasmid
56
Q

a homolog of intermediate filaments that influences the crescent shape of Caulobacter crescentus.

A

Crescentin

57
Q

uses crescentin to influence its crescent shape.

an organism

A

Caulobacter crescentus

58
Q

The actin subunit is called

A

globular or G-actin

59
Q

375-amino-acid polypeptide carrying a tightly associated ATP or ADP molecule

A

actin subunit (globular or G-actin)

60
Q

G-actin has __ amino acids and carries a tightly associated __ or __ molecule.

A
  • 375
  • ATP or ADP
61
Q

Which type of actin is found in muscle cells?

A

α-Actin

62
Q

Which types of actin are found in almost all non-muscle cells? (2)

A
  • β-actin
  • γ-actin
63
Q

subunits which assemble head-to-tail to form a tight, right-handed helix.

A

actin subunits

64
Q

What is the diameter of filamentous or F-actin?

A

8nm wide

65
Q

What are the two structurally different ends of actin filaments? (2)

A
  • minus end or “pointed end”
  • plus end or “barbed end”
66
Q

Actin filament end that is slower-growing

A

minus end or “pointed end”

67
Q

Actin filament end that is faster-growing

A

plus end or “barbed end”

68
Q

In which direction is the nucleotide-binding cleft of actin filaments directed?

A

minus end

69
Q

It is the minimum length at which random thermal fluctuations are likely to cause the filament to bend.

In actin filaments

A

persistence length

70
Q

Why is the regulation of actin filament formation important?

A

controls the shape and movement of the cell.

71
Q

the process where subunits assemble into an initial aggregate, or nucleus, stabilized by multiple subunit–subunit contacts, allowing rapid elongation.

A

Nucleation

72
Q

In actin filament nucleation, the formation of __ is rate-limiting and is further inhibited by __.

A
  • small actin oligomers
  • actin-binding proteins
73
Q

What are the three phases of in vitro polymerization of G-actin? (3)

A
  1. Nucleation
  2. Elongation
  3. Steady-state
74
Q

Lag period where G-actin aggregates into short, unstable oligomers that can act as stable seeds or nucleus once they reach a certain length.

a phase in in vitro polymerization of G-actin

A

Nucleation

75
Q

Rapid filament growth by addition of actin monomers to both ends.

a phase in in vitro polymerization of G-actin

A

Elongation

76
Q

G-actin monomers exchange with subunits at the filament ends, with no net change in total filament mass.

a phase in in vitro polymerization of G-actin

A

Steady-state

77
Q

During the __ phase of G-actin polymerization, G-actin aggregates into short, unstable __. When this reach a certain length, they act as stable __ or __ for further growth.

in vitro polymerization of G-actin

A
  • nucleation
  • oligomers
  • seeds or nuclei
78
Q

What happens to G-actin monomer concentration as F-actin filaments grow?

A

decreases

79
Q

During steady-state, G-actin monomers exchange with subunits at the __, but there is __ in the total filament mass.

in vitro polymerization of G-actin

A
  • filament ends
  • no net change
80
Q

The concentration of the pool of unassembled subunits when the steady-state phase has been reached, where subunit addition balances subunit dissociation.

actin filament dynamics

A

critical concentration (Cc)

81
Q

The ratio of the “on” and “off” rate constant, measuring the concentration of G-actin where subunit addition equals subunit dissociation.

actin filament dynamics

A

dissociation constant

82
Q

Actin filaments grow faster at the (1)__ than at the (2)__, with the (1)__ elongating (3)__ as fast as the (2)__.

A

1) plus end
2) minus end
3) 5–10 times

83
Q

This is manifested by the different rates at which G-actin adds to the two ends, with the plus end growing faster than the minus end.

A

polarity of F-actin

84
Q

__ actin filaments nucleate the polymerization of G-actin, leading to longer newly __ at the plus end compared to the minus end.

A
  • Myosin-decorated
  • polymerized (undecorated) actin
85
Q

What is the length difference of newly polymerized (undecorated) actin at the plus end compared to the minus end?

|actin filament dynamics

A

5–10 times

86
Q

What causes the difference in elongation rates at the opposite ends of an actin filament?

A

difference in critical concentration (Cc) values

87
Q

When the __ is capped, the filament can only elongate from its __.

|actin filament dynamics

A
  • plus end
  • minus end
88
Q

Elongation takes place only at the __ when the __ of a filament is blocked.

|actin filament dynamics

A
  • plus end
  • minus end
89
Q

How does the critical concentration (Cc) for polymerization compare between the plus and minus ends of an actin filament?

A

polymerization at the plus end is about six times lower than for addition at the minus end.

90
Q

1) What happens to filament growth when G-actin concentration is below Cc+?
2) What occurs when G-actin concentrations are between Cc+ and Cc-?
3) What happens to filament growth when G-actin concentration is above Cc-?

A

1) no filament growth
2) Growth occurs only at the plus end
3) no growth at both ends

91
Q

G-actin concentrations are intermediate between the Cc values for the (+) and (-) ends, with subunits continuing to be added at the (+) end and lost from the (-) end.

phase in in vitro polymerization of G-actin

A

steady-state phase

92
Q

Newly added subunits travel through the filament like they are on a __, until they reach the (-) end, where they dissociate.

|actin filament dynamics

A

treadmill

93
Q

Chemical inhibitors of actin (3)

A
  • Lantrunculin
  • Cytochalasin B
  • Phalloidin
94
Q

Chemical inhibitors of microtubules (3)

A
  • Taxol (paclitaxel)
  • Nocodazole
  • Colchicine
95
Q

What factors control the polymerization of actin? (3)

A
  • concentration
  • pH
  • concentration of salts and ATP
96
Q

Actin behavior is regulated by __ that bind actin monomers or filaments.

A

accessory proteins

97
Q

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

A

Filament half-life

98
Q

What percentage of actin is in filament form and what percentage is in soluble monomer form? (2)

A
  • 50%
  • 50%
99
Q

The cell contains proteins that bind to __, making polymerization much less favorable.

actin dynamics

A

actin monomers

100
Q

inhibits actin polymerization; it cannot associate with either the plus or minus ends and does not hydrolyze or exchange its bound nucleotide.

A

Thymosin

101
Q

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

A

Profilin

102
Q

Profilin leaves the actin filament one subunit __ and competes with __.

A
  • longer
  • thymosin
103
Q

Profilin phosphorylation and its binding to __ influence actin dynamics, promoting polymerization and filament growth.

A

inositol phospholipids

104
Q

What is a prerequisite for cellular actin polymerization?

A

Filament nucleation

105
Q

bring several actin subunits together to form a seed for filament growth.

A

Actin-nucleating proteins

106
Q

What are the two main types of actin-nucleating proteins? (2)

A
  • Arp 2/3 complex
  • formins
107
Q

Nucleates actin filament growth from the minus end, allowing rapid elongation at the plus end and can attach to the side of another filament, creating a treelike web.

actin-nucleating protein

A

Arp 2/3 complex

108
Q

nucleate the growth of straight, unbranched actin filaments.

actin-nucleating protein

A

Formins

109
Q
  • capture two actin monomers to nucleate filament growth.
  • remain associated with the rapidly growing plus end while allowing the addition of new subunits.

actin-nucleating protein

A

Formin dimers

110
Q

strongly enhanced by the association of actin monomers with profilin.

actin-nucleating protein

A

Formin-dependent actin filament growth

111
Q

alter filament behavior by binding along the side or to the ends of the filaments.

A

actin filament-binding proteins

112
Q

a side-binding protein that stabilizes and stiffens actin filaments by binding simultaneously to six or seven adjacent actin subunits, preventing interaction with other proteins and controlling muscle contraction.

actin filament-binding proteins

A

Tropomyosin

113
Q

binds to the plus end of an actin filament to stabilize it, preventing further polymerization or depolymerization

actin filament-binding proteins

A

Capping protein (CapZ)

114
Q

caps long-lived actin filaments at the minus end, binding tightly to prevent elongation and depolymerization, especially when stabilized by tropomyosin.

actin filament-binding proteins

A

Tropomodulin

115
Q

__ coat the filament completely and are present in high amounts, while __ affect filament dynamics at the ends.

actin filament-binding proteins

A
  • Side-binding proteins
  • end-binding proteins
116
Q

break actin filaments into many smaller fragments, generating new filament ends that can nucleate further filament growth and promoting the depolymerization of older filaments.

A

Severing proteins

117
Q

activated by high levels of cytosolic Ca²⁺. It interacts with the side of an actin filament and binds until a thermal fluctuation creates a gap, allowing it to insert itself and break the filament.

severing proteins

A

Gelsolin superfamily/gelsolin

118
Q

an actin depolymerizing factor that binds along the length of the filament, causing it to twist more tightly, which weakens the contacts between actin subunits and preferentially targets ADP-containing actin filaments for dismantling.

severing proteins

A

Coffin

119
Q

Actin filaments containing __ are resistant to __, making them more stable compared to those with __, which are more readily dismantled by severing proteins like cofilin.

severing proteins

A
  • ATP
  • depolymerization
  • ADP
120
Q

What are the types of actin filament arrays? Add short description (3)

A
  • Dendritic networks – Arp 2/3 complex
  • Bundles networks – made of the long, straight filaments produced by formins
  • Weblike (gel-like) networks – not well-defined
121
Q

What determines the differences in actin networks?

A

specialized accessory proteins

122
Q

Proteins that cross-link actin filaments into a parallel array.

specialized accessory proteins; actin filament types of arrays

A

bundling proteins

123
Q

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

specialized accessory proteins; actin filament types of arrays

A

gel-forming proteins

124
Q

enables stress fiber and other contractile arrays to contract.

actin filament array

A

Myosin II

125
Q

allows for the close packing of actin filaments; it is not contractile.

actin filament array

A

Fimbrin

126
Q

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

actin filament array

A

α-Actinin

127
Q

tight packing prevents myosin II from entering bundle

actin filament array

A

parallel bundle

128
Q

loose packing allows myosin II to enter bundle

actin filament array

A

contractile bundle

129
Q
  • forms a loose and highly viscous gel by clamping together two actin filaments roughly at right angles, creating actin filament webs or gels.
  • connects and coordinates a wide variety of cellular processes with the actin cytoskeleton.

actin-binding protein

A

filamin

130
Q

can lead to defects in nerve-cell migration during early embryonic development, resulting in periventricular heterotopia, where cells in the periventricular region of the brain fail to migrate to the cortex and instead form nodules.

a mutation

A

Filamin A gene mutations

131
Q

a web-forming, long, flexible protein made out of four elongated polypeptide chains, consisting of two α subunits and two β subunits.

actin-binding protein

A

Spectrin

132
Q

In RBCs, __ is concentrated beneath the plasma membrane, forming a two-dimensional weblike network that provides a strong, yet flexible cell cortex, allowing RBCs to spring back to their shape.

actin-binding protein

A

spectrin

133
Q

are crucial for regulating actin dynamics, facilitating the assembly and disassembly of actin filaments, which in turn enables motility and force production in various cellular processes.

A

Accessory proteins

134
Q
  • Bacteria and viruses that use components of the host cell actin cytoskeleton to move through the __.
  • To move around in a cell and invade neighboring cells, overcome this problem by recruiting and activating the __ at their surface.
A
  • cytoplasm
  • Arp 2/3 complex
135
Q
  • What is an example of a bacterium that recruits the Arp 2/3 complex?
  • It recruits and activates Arp2/3 complex; forms a “__.”
A
  • Listeria monocytogenes.
  • comet tail

Cell and Molecular Biology (20 decks)

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