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CMB > Cytoskeleton > Flashcards

Cytoskeleton Flashcards

1
Q

What is the primary function of actin filaments?

A
  1. Shape of the cell’s surface
  2. whole-cell locomotion
  3. pinching of one cell into two
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2
Q

Three families of protein filaments

A
  1. Actin filaments
  2. Microtubules
  3. Intermediate filaments
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3
Q

What role do microtubules play in the cell?

A
  1. Determine the positions of membrane-enclosed organelles
  2. Direct intracellular transport
  3. Form the mitotic spindle
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4
Q

What is the function of intermediate filaments?

A

Provide mechanical strength

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5
Q

What characterizes cytoskeletal systems?

A

Dynamic and adaptable, can change or persist according to need

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6
Q

Where are actin filaments located in animal cells?

A

Underlie the plasma membrane

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7
Q

Cell surface projections formed by Actin filaments:

A

1.Lamellipodia
2. Filopodia

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8
Q

Where are microtubules found?

A

In a cytoplasmic array that extends to the cell periphery.

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9
Q

What cellular structures are formed by microtubules?

A

Cilia and the mitotic spindle

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10
Q

What is the role of intermediate filaments in epithelial cells?

A

Forms a protective cage for DNA

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11
Q

The cytoskeleton is responsible for large-scale cellular _______.

A

polarity

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12
Q

Polarized epithelial cells maintain the critical differences between the _____ and ______ .

A

Apical surface and basolateral surface

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13
Q

What are the subunits that make up actin filaments?

A

Actin subunits

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14
Q

What are the subunits that make up microtubules?

A

tubulin subunits

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15
Q

What is the difference between the plus end and minus end of an actin filament?

A

Plus end grows faster than minus end

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16
Q

Microtubules are built of ________ .

A

13 protofilaments

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17
Q

True or False: Intermediate filament subunits are symmetrical and do not catalyze hydrolysis of nucleotide.

A

True

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18
Q

Proteins that bind to the polarized cytoskeletal filament and us the energy derived from ATP hydrolysis to move along with it.

A

Motor Proteins

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19
Q

Bacterial homolog of tubulin

A

FtsZ (forms z-ring)

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20
Q

Bacterial homolog of actin

A

MreB and Mbl

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21
Q

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

A
  1. Nucleation
  2. Elongation
  3. Steady-state
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22
Q

What is the function of motor proteins in relation to cytoskeletal filaments?

A

Move along the filament using energy from ATP hydrolysis

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23
Q

What is ParM in bacteria?

A

Bacterial actin homolog that helps in plasmid segregation

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24
Q

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

A

Difference in critical concentration values at the two ends

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25
Q

What is the structural form of actin filaments?

A

Right-handed helix, 8nm wide

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26
Q

What is the nucleotide-binding cleft of actin filaments directed towards?

A

The minus end

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27
Q

The stiffness of of a filament can be characterized by its ________ .

A

Persistence length

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28
Q

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

A

A difference in Cc values at the two ends

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29
Q

Which end of an actin filament can elongate when the plus end is capped?

A

Minus end

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30
Q

At what concentration of G-actin is there no filament growth?

A

Below Cc+

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31
Q

When G-actin concentration is between Cc+ and Cc-, where does growth occur?

A

Only at the (+) end

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32
Q

What happens when G-actin concentration is above Cc-?

A

No growth at both ends

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33
Q

What is the steady-state phase in actin dynamics?

A

G-actin concentrations intermediate between the Cc values for the (+) and (-) ends

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34
Q

What analogy describes the movement of newly added subunits in an actin filament?

A

As if on a treadmill

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35
Q

What is filament half-life?

A

A measure of how long an individual actin monomer spends in a filament

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36
Q

Keep the excess actin monomers in a sequestered state, preventing spontaneous polymerization

A

Thymosin

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37
Q

competes with thymosin for binding to actin monomers; promotes filament assembly by delivering monomers to the plus end

A

Profilin

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38
Q

Bring several actin subunits together to form a seed

A

Actin-nucleating factors

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39
Q

Nucleates actin filament growth from the minus end

A

Arp 2/3 Complex

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40
Q

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

A

Formins

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41
Q

What do actin filament-binding proteins do?

A

Alter filament behavior

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42
Q

Side-binding protein that stabilizes and stiffens actin filaments and can prevent actin filaments from interacting with other proteins.

A

Tropomyosin

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43
Q

Binds at the plus end, stabilizing an actin filament

A

Capping protein (Cap Z)

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44
Q

Responsible for the capping of exceptionally long-lived actin filaments in the muscle.

A

Tropomodulin

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45
Q

Proteins that break an actin filament into many smaller filaments, generating new filament ends

A

Severing proteins

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46
Q

Two types of severing proteins:

A
  1. Gelsolin
  2. Cofilin
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47
Q

What is gelsolin activated by?

A

High levels of cytosolic Ca2+

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48
Q

Acts as an actin depolymerizing factor that binds to and twists actin filaments

A

Cofilin

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49
Q

Actin filaments in animal cells are organized into several types of arrays:

A
  1. Dendritic networks
  2. Bundles
  3. Web-like (gel-like) networks
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50
Q

What type of actin filament array is formed by the Arp 2/3 complex?

A

Dendritic networks

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51
Q

The motor protein that enables stress fibers and other contractile arrays to contract.

A

Myosin II

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52
Q

Facilitates the close packing of actin filaments

A

Fimbrin

53
Q

Cross-links oppositely polarized actin filaments into loose bundles.

A

α-actinin

54
Q

Promotes the formation of a loose and highly vicuous gel by clamping together two actin filaments.

A

Filamin

55
Q

Mutations in the filamin A gene cause defects in ______ .

A

Nerve-cell migration during early embryonic development

56
Q

What is the structure of spectrin?

A

Long, flexible protein made out of four elongated polypeptide chains

57
Q

What do myosin heads do with ATP?

A

Bind and hydrolyze ATP

58
Q

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

A

Myosin II

59
Q

What are the motor proteins that interact with actin filaments?

A

Myosin

Myosin and actin motor proteins use structural changes to produce cyclic interactions.

60
Q

A cylindrical structure 1-2 μm in diameter which consists of sarcomeres.

A

Myofibrils

61
Q

A long, repeated chain of tiny contractile units about 2.2 μm long.

A

Sarcomeres

Sarcomeres give the vertebrate myofibril its striated appearance.

62
Q

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

A

Sarcomere shortening

63
Q

Components of a sarcomere:

A
  1. Thin filaments
  2. Thick filaments
64
Q

What initiates muscle contraction?

A

Rise in cytosolic Ca2+ concentration

This signal passes to skeletal muscle from the nerve.

65
Q

tube-like extensions of the muscle cell membrane that conduct electrical signals into the cell, triggering coordinated calcium release for muscle contraction.

A

Transverse tubules (T tubules)

66
Q

Is an elongated protein that binds along the groove of the actin filament helix. It stabilizes and stiffens the filament.

A

Tropomyosin

It interferes with the binding of myosin head when in its normal state.

67
Q

Troponin is a complex of three polypeptides:

A

troponin T, troponin I, and troponin C

68
Q

What complex pulls tropomyosin out of its binding groove?

A

Troponin I-T complex

This action allows myosin heads to bind to actin.

69
Q

Is a regulatory protein that activates MLCK in smooth muscle cells upon binding with calcium, leading to muscle contraction.

A

Calmodulin

70
Q

Induces the phosphorylation of smooth muscle myosin on one of its two light chains upon activation of calmodulin.

A

Myosin light-chain kinase (MLCK)

It is activated by Ca2+-bound calmodulin.

71
Q

A genetic condition commonly associated with heart enlargement, abnormally small coronary vessels, cardiac arrhythmias, and sudden death in young athletes.

A

Familial hypertrophic cardiomyopathy

It is a genetically dominant inherited condition.

72
Q

Caused by a minor missense mutation in the cardiac actin gene, which results in early heart failure.

A

Dilated cardio myopathy

73
Q

Two-headed myosin associated with organelle transport along actin filaments

A

Myosin V

It moves processively along actin filaments without letting go.

74
Q

A heterodimer formed from α-tubulin and β-tubulin

A

Tubulin subunit

75
Q

What is γ-tubulin?

A

A protein involved in the nucleation of microtubule growth

76
Q

Specific intracellular location where microtubules are nucleated

A

Microtubule-organizing center (MTOC)

77
Q

A complex that includes γ-tubulin and accessory proteins, forming a template for microtubule growth.

A

γ-tubulin ring complex (γ-TuRC)

78
Q

A microtubule-organizing center near the nucleus that nucleates microtubules at their minus ends, while plus ends point outward, continuously growing and shrinking.

A

Centrosome

79
Q

Cylindrical structures embedded in the centrosome, arranged at right angles.

A

Centrioles

80
Q

Where microtubule nucleation takes place.

A

Pericentriolar material

81
Q

The centrosome exhibits a _______ configuration with dynamic plus ends pointing outward

A

Aster-like

82
Q

Proteins that bind to microtubules to stabilize them and mediate interactions with other cell components.

A

Microtubule-associated proteins (MAPs)

83
Q

A MAP with a long projecting domain that forms bundles of widely spaced, stable microtubules

A

MAP2

84
Q

A MAP with a shorter projecting domain that forms closely packed microtubule bundles.

A

tau

85
Q

Binds to microtubule ends and pry protofilaments apart

A

Catastrophe factors (kinesin-13)

86
Q

Protects microtubule minus ends from catastrophe factors

A

Nezha/Patronin

87
Q

A protein that promotes microtubule polymerization and counters catastrophe factors

A

XMAP215

88
Q

Proteins that accumulate at microtubule plus ends and assist in their growth

A

Plus-end tracking proteins (+TIPs)

89
Q

Binds to tubulin subunits, preventing their addition to microtubules and promoting microtubule shrinkage.

A

Stathmin (Op18)

90
Q

A protein composed of two subunits: one severs microtubules (via ATP hydrolysis), and the other directs katanin to the centrosome.

A

Katanin

91
Q

Two major classes of microtubule-based motor proteins:

A
  1. Kinesins
  2. Dyneins
92
Q

Carries membrane-enclosed organelles away from the cell body toward the axon terminal by walking toward the plus end of microtubules.

A

Kinesin-1

93
Q

Composed of 1–3 heavy chains (with motor domains) and various intermediate, light-intermediate, and light chains.

A

Dyneins

94
Q

Two major branches of the dynein family

A
  1. Cytoplasmic dyneins
  2. Axonemal dyneins
95
Q

Dyneins that are homodimers of two heavy chains

A

Cytoplasmic dyneins

96
Q

Dynein that handles organelle/mRNA trafficking, centrosome and nucleus positioning, and spindle construction in mitosis/meiosis

A

Cytoplasmic dynein I

97
Q

Dynein found in ciliated eukaryotes, it transports materials from the cilia’s tip to its base (intraflagellar transport).

A

Cytoplasmic dynein II

98
Q

They enable the rapid microtubule sliding that powers cilia and flagella movement.

A

Axonemal dyneins (ciliary dyneins)

99
Q

A protein complex associated with dynein to translocate organelles

A

Dynactin

100
Q

What are cilia and flagella?

A

Hairlike structures built from microtubules that enable motility

101
Q

The central, microtubule-based core of cilia and flagella, responsible for their movement.

A

Axoneme

102
Q

What are axonemal dyneins?

A

Proteins that form bridges between neighboring doublet microtubules around the circumference of the axoneme

103
Q

A nonmotile counterpart of cilia and flagella; specialized cellular compartments or organelles

A

Primary cilium

104
Q

The most diverse intermediate filament family, composed of type I (acidic) and type II (neutral/basic) keratin proteins

A

Keratins

105
Q

Intermediate filaments abundant in the axons of vertebrate neurons

A

Neurofilaments

106
Q

Intermediate filaments found in muscle cells, where it forms a scaffold around the Z-disc of the sarcomere

A

Desmin

107
Q

They facilitate cell-cell contact

A

Desmosomes

108
Q

What do neurofilaments consist of?

A

NF-L, NF-M, and NF-H

109
Q

Intermediate filaments are interconnected with other cytoskeletal components through linker proteins called _______ .

A

Plakins

110
Q

Serve as scaffolds for proteins controlling various cellular processes including transcription and signal transduction

A

A-type lamins

111
Q

A family of proteins that link the intermediate filament network to the rest of the cytoskeleton

A

Plakins

112
Q

One-dimensional protrusions formed by migrating growth cones of neurons and some fibroblasts

A

Filopodia

113
Q

Two-dimensional sheet like structures formed by epithelial cells and fibroblasts

A

Lamellipodia

114
Q

What is retrograde flow in the context of cell migration?

A

Retrograde flow

115
Q

The front end of the cell remains structurally and functionally distinct from the back end.

A

Cell Migration

116
Q

Steps in the cycle of cell migration

A
  1. Protrusion
  2. Attachment
  3. Traction
117
Q

A step in the cell migration which involves pushing the plasma membrane out in front of the cell

A

Protrusion

118
Q

In this step, the actin cytoskeleton connects
across the plasma membrane to the substratum

A

Attachment

119
Q

In this step the bulk of the trailing cytoplasm is drawn forward

A

Traction

120
Q

Types of protrusive structures:

A
  1. Filopodia
  2. Lamellipodia
  3. Invadopodia
  4. Blebbing
121
Q

Formed by migrating growth
cones of neurons and some type of fibroblast; one-dimensional; contain a core
of long, bundled actin filaments

A

Filopodia

122
Q

Formed by epithelial cells and fibroblast; two-dimensional sheetlike structures; contain a cross0linked mesh of actin filaments

A

Lamellipodia

123
Q

Actin-rich protrusion; three-dimensional; important for cells to cross tissue barriers

A

Invadopodia and podosomes

124
Q

Protrusion formation that depends on hydrostatic pressure within the cell; generated by the contraction of actin and myosin

A

Blebbing

125
Q

Members of the Rho protein family

A
  1. Cdc42
  2. Rac
  3. Rho
126
Q

Promotes actin polymerization and bundling to form filopodia.

A

Cdc42

127
Q

Activates actin polymerization at the cell periphery and forms sheet-like lamellipodial extensions.

A

Rac

128
Q

Bundles actin filaments with myosin II filaments into stress fibers and clusters integrins to form focal adhesions.

A

Rho

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