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My Packs: (WIZEPREP) (BIO 2382) > Chapter 4: 4.1 Cytoskeletal Proteins > Flashcards

Chapter 4: 4.1 Cytoskeletal Proteins Flashcards

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1
Q

What is the cytoskeleton?

A

A network of protein filaments that extends throughout the cytoplasm

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2
Q

Cystoskeletal filaments are…

(2 points)

A
  1. Dynamic
  2. Can re-organize
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3
Q

Cytoskeletal filaments are dynamic and can re-organize, what does this allow?

A

Allows cells to:
* Change shape
* Interact with the enivronment
* Move
* Organize cellular compartments

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4
Q

How many types of protein filaments are in the cytoskeleton? List them out

A

3
1. Intermediate Filaments
2. Microtubules
3. Actin Microfilaments

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5
Q

Describe:

Intermediate filaments

A

Rope-like filaments composed of a family of keratin proteins

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6
Q

Describe:

Microtubules

A

Hollow cylinders made of tubulin dimers

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7
Q

Describe:

Actin microfilaments

A

Helical polymers of actin protein

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8
Q

List the functions of:

Intermediate filaments

A
  • Provide mechanical strength
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9
Q

List the functions of:

Microtubules

A
  • Involved in organization of organelles and vesicles
  • Form the mitotic spindle
  • Major component of flagella and cilia
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10
Q

List the functions of:

Actin microfilaments

A
  • Involved in cellular movement
  • Involved in skeletal muscle contraction
  • In plants, involved in organization of organelles and vesicles
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11
Q

Provide:

The etymology for Intermediate filaments

A

Named for their intermediate size, relative to actin and microtubules

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12
Q

True or False:

Flagella and cilia are not the only type of cytoskeletal structure in prokaryotic cells namely bacteria

A

False, they are

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13
Q

What do intermediate filaments enable cells to do? How?

A

Enables cells to withstand mechanical stress, by distributing the effects of locally applied force

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14
Q

What do intermediate filaments consist of?

A

Long, twisted strands of fibrous proteins
* ~10 nm in diameter
* Composed of various helical protein types (e.g. keratin)

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15
Q

True or False:

Intermediate filaments are not dynamic

A

True, they are not as dynamic as microtubules and actin filaments

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16
Q

Where are intermediate filaments located in the body?

A

Have rolls in:
* Cell junctions
* Muscle contraction
* Neurons
* Nuclear structure

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17
Q

True or False:

Intermediate filaments usually work with microtubules and actin filaments to carry out their functions

A

True

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18
Q

Describe:

Monomer Intermediate Filaments

A
  • Has a central rod-shaped domain (elongated α-helix)
  • Has unstructured terminal domains (not globular like microtubules and microfilaments)
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19
Q

True or False:

Central domains of different intermediate filament types are different in size and primary structure

A

False, they are similar in size and primary structure

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20
Q

What are exposed on the surface of intermediate filaments? Why?

A

Terminal domains, allos interactions with cytoplasmic components

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21
Q

Describe:

Dimer Intermediate Filaments

A

Coiled coil; two monomers intertwined

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22
Q

Describe:

Tetramer Intermediate Filaments

A

Two dimers, running in opposite directions
* Dimers do not overlap completely, but are instead staggered

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23
Q

True or False:

The two ends of tetramers are the same

A

True

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24
Q

Are intermediate filaments non-polar? Microtubules? Actin microfilaments?

A

Intermediate filaments are non-polar
* Microtubules and actin microfilaments are polar

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25
Q

How do tetramer intermediate filaments assemble?

A

Assemble into a rope-like intermediate filament
* Interacts at the ends of each tetramer and at the sides

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26
Q

The extracellular matric can also maintain a connect between cells with the help of…

A

Cytoskeletal proteins

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27
Q

Define:

Desmosomes

A

Connections made by intermediate filaments, keep cells tightly bound (e.g. skin cells)

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28
Q

Define:

Gap junctions

A

Channels that form between cells to allow molecules to be shared between cells

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29
Q

Define:

Tight junctions

A

Held together by cell adhesion molecules called CAMs

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30
Q

What are examples of CAMs?

A
  • Cadherin
  • Integrins
  • Selectins
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31
Q

What are microtubules crucial for?

A

The interior organization of cells

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32
Q

Explain:

Role of microtubules during interphase

A

Associate with motor proteins that transport or position organelles and vesicles

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33
Q

Explain:

Role of microtubules during cell division

A

Form the mitotic spindle
* Ensures that chromosomes are correctly divided between the two daughter cells

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34
Q

Microtubules form the core of…

A

Flagella and Cilia

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35
Q

True or False:

Microtubules are dynamic

A

True

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36
Q

What does it mean that microtubules are “dynamic”?

A

They are able to rapidly disassemble and reassemble

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37
Q

Define:

Dynamic instability

A

The ability to switch between phases of assembly and disassembly

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38
Q

How many categories of microtubules are there? What are they?

A

2 main categories:
1. Cytoplasmic
2. Axonemal

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39
Q

Describe:

Cytoplasmic microtubules

A
  • More dynamic
  • Located throughout cytosol
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40
Q

Describe:

Axonemal microtubules

A
  • Less dynamic and more stable
  • Located in cilia and flagella
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41
Q

Microtubules originate/grow outward from…

A

Microtubule Organizing Centres (MTOCs)

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42
Q

Define:

Centrosomes

A

A type of MTOC found in animal cells
* Consist of a pair of centrioles surrounded by various proteins, including the γ-tubulin ring complex

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43
Q

Define:

Protofilament

A

A single chain of tubulin dimers, alternating between α- and β-tubulin

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44
Q

Describe:

Microtubule structure (in terms of protofilaments)

A

13 protofilaments bind laterally to form a hollow, tube-like structure

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45
Q

Describe:

Microtubule size in comparison to other fibers

A
  • Larger (~10-25 nm) than actin microfilaments
  • Larger than intermediate filaments
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46
Q

State:

The Function of Microtubules

(4 points)

A
  • Structural support
  • Organization of cytoplasm - positioning of organelles
  • Transport (“roads” for motor proteins)
  • Segregation of chromosomes during cell division (mitotic spindle)
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47
Q

Microtubules are dynamic. What does that mean?

A

They are abel to rapidly diassemble and reassemble

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48
Q

The microtubules’ ability to switch between phases of assembly and disassembly is called…

A

Dynamic Instability

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49
Q

Describe:

Tubulin

A

A heterodimer of α-tubulin and β-tubulin

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50
Q

What does β-tubulin bind to?

A

GTP
* Over time is hydrolyzed to GDP (has GTPase activity)

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51
Q

Describe:

GTP-tubulin dimers

A

Have straight conformation
* Can more easily assemble

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52
Q

Describe:

GDP-tubulin dimers

A

Have a curved conformation
* Are prone to disassemble

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53
Q

In microtubules:

When is assembly promoted?

A

If most of the plus-end tubulin dimers are GTP-bound
* Creates a GTP cap, with a straight conformation

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54
Q

What does the loss of a GTP cap mean?

A

Curved dimers are exposed at the plus end
* Causes rapid disassembly

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55
Q

In vitro, microtubules can assemble and disassemble…

A

Spontaneously

56
Q

In vitro, microtubules can assemble and disassemble spontaneously. What is this driven by?

A

Driven by the concentration of tubulin dimers and by whether GTP or GDP is bound to β-tubulin

57
Q

In the cell, what is assemble and disassembly controlled by?

A

Microtubule-associated proteins
* Allows the cell to control the organization of microtubules

58
Q

True or False:

Microtubules have structural polarity

A

True

59
Q

How does structural polarity work in microtubules?

A
  • β-tubulin is exposed at the plus end
  • α-tubulin is exposed at the minus end
60
Q

Why is structural polarity important for microtubules?

A

Crucial for guiding motor proteins (intracellular transport)

61
Q

True or False:

The plus end is less dynamic

A

False, it is more dynamic (rates of assembly and disassembly are higher the plus end)

62
Q

When microtubules assemble/disassemble, what happens?

A

Addition or loss of tubulin subunits

63
Q

True or False:

Dynamic instability of microtubules can be experimentally altered using drugs

A

True

64
Q

What effect do Microtubule-stabilizing drugs have?

A

Prevents depolymerization

65
Q
  1. Give an example of a Microtubule-stabilizing drug
  2. State how it works
A
  1. Taxol
  2. Used in treatment of various cancers, as stabilization of microtubules can prevent cell division
66
Q

What effects do Microtubule-detabilizing drugs have?

A

Inhibit polymerization (e.g. by binding/sequestering or modifying free tubulin dimers)

67
Q

Give examples of Microtubule-destabilizing drugs

A
  • Colchicine
  • Colcemid
  • Binblastine
  • Vincristine
68
Q

Free tubulin dimers and microtubules exist in an ———–, with growth or shrinkage of the microtubule occuring depending on the ————- of available ——-

A
  • Equilibrium
  • Concentration
  • Tubulin
69
Q

Define:

Critical Concentration

(Microtubules)

A

The concentration of tubulin at which net growth/shrinkage is zero
(Can also be applied to actin polymerization and depolymerization)

70
Q

Most differentiated animal cells have structural and functional polarity, which reflects the…

A

Asymmetry of the microtubule array (network)

71
Q

Certain microtubule-associated proteins may stabilize the —- ends of microtubules, or cause them to form ——-

A
  • Plus
  • Bundles
72
Q

How can stabilized microtubules maintain organization within the cell?

A

By transporting or positioning organelles, vesicles etc.

73
Q

What are actin filaments involved in?

(3 points)

A
  • Involved in cellular movements
  • Required for phagocytosis
  • Required for cell division
74
Q

Where are actin filaments usually located?

A

Just below the cell membrane

75
Q

True or False:

Actin filaments are the smallest of the cytoskeletal components

A

True (~6 nm in diameter)

76
Q

True or False:

Actin microfilaments are polar but they do not have dynamic instability

A

False, they are polar AND they can assemble and disassemble (dynamic instability)

77
Q

What is f-actin? What is it composed of?

A

Filamentous actin
* Composed of monomers of globular actin (g-actin)

78
Q

State:

Actin filament functions

(4 points)

A
  • Structural support
  • Movement of organelles and vesicles
  • Cell division
  • Muscle contraction
79
Q

Forming an Actin Filament:

What is free floating actin called?

A

G-actin

80
Q

Forming an Actin Filament:

How does a filament of actin form?

A

When ADP becomes ATP, it triggers formation of the filament called F-actin

81
Q

True or False:

In forming an actin filament, the plus end is the growing end

A

True

82
Q

What is the role of the minus end in forming an actin filament?

A

Shrinking end
* Where ATP is hydrolyzed to ADP

83
Q

Actin monomers are bound to —, which is ———- to — following incorporation into the ————-

A
  • ATP
  • Hydrolyzed
  • ADP
  • Microfilament
84
Q

What is the plus end of an actin microfilament characterized by?

A

A higher rate of growth

85
Q

True or False:

Both the plus and minus ends of actin microfilaments can polymerize

A

True, if the concentration of actin monomers is sufficiently high

86
Q

Are actin microfilaments bigger or smaller than the other cytoskeletal components?

A

Smaller (5-9 nm)

87
Q

In Actin microfilaments:

—– and associated —— —— form a ———– —- during ———–

A
  • Actin
  • Myosin motors
  • Contractile ring
  • Cytokinesis
88
Q

Define:

Treadmilling

(Actin microfilaments)

A

An equilibrium state in which monomers are lost from the minus end, while (other) monomers are added to the plus end (also occurs in microtubules)

89
Q

What happens at the plus end of actin microfilaments?

A

Actin-ATP monomers binds to the growing microfilament faster than ATP in subunits of the existing microfilament is hydrolyzed

90
Q

What happens at the minus end of actin microfilaments?

A

Actin-ATP is hydrolyzed faster than new actin-ATP monomers can be added

91
Q

When does the actin microfilament stay the same length?

A

When the rate of loss at the minus end and the rate of gain at the plus end are equal

92
Q

Actin-targeted drugs can alter…

A

The dynamic behaviour of actin microfilaments

93
Q

Define and give example(s) of:

Polymerization-inhibiting drugs

A

Bind/sequester free actin, or cap the plus end
* Latrunculin (binds free actin)
* Cytochalasin (caps plus end)

94
Q

Define and give example(s) of:

Microfilament-stabilizing drugs

A

Prevent depolymerization
* Phalloidin

95
Q

Actin-binding proteins can also…

A

Alter the dynamicity and organization of actin microfilaments

96
Q

Define and give example(s) of:

Monomer-sequestering proteins

A

Bind free actin, preventing polymerization
* Thymosin

97
Q

Define and give example(s) of:

Nucleating proteins

A

Initiate microfilament formation/polymerization
* No equivalent to an MTOC, so actin microfilaments are nucleated at multiple sites in the cell
* Arp2/3

98
Q

Define:

Severing proteins

A

Sever microfilaments into smaller fragments

99
Q

Define:

Bundling proteins

A

Link together parallel microfilaments to form bundles

100
Q

Define:

Cross-linking proteins

A

Link together perpendicular microfilaments to form a network

101
Q

Define:

Capping proteins

A

Bind to the plus end, blocking polymerization

102
Q

List:

Actin-targeted drugs

(2 points)

A
  • Polymerization-inhibiting drugs
  • Microfilament-stabilizing drugs
103
Q

List:

Actin-binding proteins

(7 points)

A
  • Monomer-sequestering proteins
  • Nucleating proteins
  • Severing proteins
  • Bundling proteins
  • Cross-linking proteins
  • Capping proteins
  • Side-binding proteins
104
Q

Define:

Side-binding proteins

A

Bind along the side (rather than the ends) of a microfilament

105
Q

True or False:

Actin may organize into different types of arrays

A

True

106
Q

How does actin organize into different types of arrays?

A

Basaed on linking of F-actin by different actin-binding proteins

107
Q

What arrays may actin organize into?

A
  • Parallel bundles
  • Contractile bundles
  • Cross-linked gel
108
Q

Describe:

Parallel bundles

(Actin)

A

Linked by fimbrin
* In filopodia, microvilli

109
Q

Describe:

Contractile bundles

(Actin)

A

Arranged in an antiparallel manner
* Linked by α-actinin and other proteins
* In stress fibres, contractile ring

110
Q

Describe:

Cross-linked gel

(Actin)

A

Random orientation of F-actin
* Linked by filamin
* Found at the cell cortex
* Involved in amoeboid motion and cytoplasmic streaming

111
Q

What is gelsolin?

A

An enzyme
* Can break up actin gels

112
Q

Define:

Cell cortex

A

A region just beneath the plasma membrane

113
Q

What is the function of actin in the cell cortex?

A

Provides support/mechanical strength for the plasma membrane

114
Q

True or False:

Actin in the cell cortex influences cell shape

A

True (e.g. in red blood cells)

115
Q

What are integrins?

A

Integrins anchor internal F-actin to the extracellular matrix

116
Q

How many related processes are essential for actin-mediated cell movement?

A

Three

117
Q

What are the 3 related processes essential for actin-mediated cell movement?

A
  1. The cell pushes out protrusions at the leading edge of the moving cell
  2. Protrusions adhere to a surface, providing anchor points
  3. Using the integrin anchors, the cell drags itself forward
118
Q

Define:

Lamellipodia

A

Thin, sheet-like protrusions
* Contain a branched network of microfilaments
* Oriented such that the plus ends are close to the plasma membrane

119
Q

In actin-mediated cell movement:

What directs actin branching?

A

Nucleating and side-binding proteins

120
Q

In actin-mediated cell movement:

  • Plus ends are protected by…
  • Minus ends are…
A
  • Plus ends are protected by capping proteins
  • Minus ends are severed
121
Q

In actin-mediated cell movement:

What results from plus end capping and minus end severing?

A

Actin network and the membrane are pushed forward

122
Q

Define:

Filopodia

A

Thin, rod-like protrusions
* Contain parallel bundles of microfilaments

123
Q

In actin-mediated cell movement:

What do filopodia rely on?

A

Formins
* Promotes linear growth instead of branching

124
Q

In actin-mediated cell movement:

What helps the cell detach and move?

A

Contractile bundles in the body of the cell

125
Q

In actin-mediated cell movement:

What is contraction mediated by?

A

Myosin II

126
Q

In actin-mediated cell movement:

What is the function of Lamellipodia and Filopodia in cell movement?

A

“Explore” for a favourable contact point

127
Q

In actin-mediated cell movement:

What happens when a protrusion makes contact with a favourable surface?

A

Integrins create an anchor

128
Q

What is chemotaxis?

A

When environmental factors trigger cell movement

129
Q

What is chemotaxis mediated by?

A

Rho proteins

130
Q

Rho proteins are a type of…

A

Ras GTPase

131
Q

What are the Rho proteins that mediate chemotaxis?

A
  1. Cdc42
  2. Rac
  3. Rho
132
Q

What is the function of Cdc42 in chemotaxis?

A

Triggers filopodia formation

133
Q

What is the function of Rac in chemotaxis?

A

Triggers lamellipodia formation

134
Q

What is the function of Rho in chemotaxis?

A

Activates fiber formation and contractile movement

135
Q

Rho proteins activate…

A

Genes and proteins involved in different types of cell movement

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