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MCBG > 9.2.16 Lecture > Flashcards

9.2.16 Lecture Flashcards

1
Q

The cytoskeleton involves a dynamic array of what three interacting filaments?

A
  1. Actin (smallest, 5-7nm diameter)
  2. Microtubules (largest, 25 nm diameter)
  3. Intermediate filaments (medium, 10 nm diameter)
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2
Q

What are the 6 major functions of actin?

A
  1. Dictate cell shape
  2. Mediate cell adhesion
  3. Polarization
  4. Phagocytosis
  5. Muscle contraction
  6. Cell migration
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3
Q

Actin is localized below the ___.

A

Cell membrane

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4
Q

What determine cell shape and surface area?

A

Cortical actin and actin arrays

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5
Q

What are the two types of cell adhesion mediated by actin?

A
  1. Cell-cell, through adherens junctions

2. Cell-matrix through focal contacts

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6
Q

Actin arrays partition polarized cells into ___ and ___ compartments.

A

Apical; basal

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7
Q

The ___ is an actin-based structure.

A

Phagosome

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8
Q

Bundles of actin filaments are used by ___ for muscle contraction.

A

Myosin motors

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9
Q

What are the four general instances needing cell migration?

A
  1. Development
  2. Wound healing
  3. Immune system
  4. Cancer metastasis
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10
Q

What is the soluble subunit of actin?

A

Actin monomer

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11
Q

Describe the structure of the actin monomer.

A

Globular, contains ATP when in the cytosol, ADP when in the filament, has + and - end (polar)

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12
Q

What is the actin filament made of?

A

Flexible helix of 2 protofilaments

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13
Q

Actin monomers and filaments are ___. This gives it ___. Which end is more dynamic?

A

Polar; directionality; +

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14
Q

___ regulate actin filament assembly and disassembly.

A

Accessory proteins

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15
Q

Small soluble actin subunits are in ___ with large filamentous polymers.

A

Equilibrium

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16
Q

A signal can lead to disassembly of filaments and rapid ___ of subunits, followed by reassembly at a ___ site.

A

Diffusion; new

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17
Q

What are the three phases to actin filament assembly?

A
  1. Nucleation (lag phase)
  2. Elongation (growth phase)
  3. Steady state equilibrium (equilibrium phase)
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18
Q

What is the rate limiting step to actin filament assembly?

A

Nucleation

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19
Q

What is the critical concentration?

A

The concentration of actin monomers at steady state

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20
Q

What happens to the kinetics of actin formation if actin “nuclei” are added directly?

A

Removes the nucleation/lag phase

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21
Q

Actin is nucleated at the ___ end.

A

Minus

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22
Q

Nucleation occurs preferentially at the ___, which allows for cell surface structures to form.

A

Cell membrane

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23
Q

Nucleation occurs via what protein(s)?

A

Actin related proteins (ARP) -> ARP2 and ARP3

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24
Q

ARP binds pre-existing filaments at a ___ angle.

A

70 degree

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25
Q

What modulates filament growth and localization? What do each of these do?

A

End binding proteins (ARP and Cap Z) - ARP caps and nucleates the minus end, CapZ binds and stabilizes the + end.

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26
Q

___ modulate filament elongation. These are ___ (less or more) efficient than end binding proteins.

A

Subunit binding proteins; less

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27
Q

___ modulate filament stability and orientation. This includes what protein?

A

Filament binding proteins; cofilin (actin depolymerization factor that preferentially binds to ADP subunits in existing actin filaments.)

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28
Q

Filamentous actin contains enzymes to…

A

…hydrolyze ATP present in subunits.

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29
Q

ATP hydrolysis converts ___ form to ___ form.

A

T (stabilizes + end of filament); D

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30
Q

Nucleotide hydrolysis results in treadmilling. What is this?

A

+ end addition is fast and hydrolysis lags behind. - end addition is slow and hydrolysis catches up. This creates a flux of subunits.

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31
Q

A high critical concentration is favorable for ___; a low critical concentration is favorable for ___.

A

Loss; addition

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32
Q

Critical concentration of ___ is less than that of ___.

A

T; D

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33
Q

Describe actin protrusion in lamellipodia.

A

Net filament diassembly occurs behind the leading edge via cofilin binding to the ADP form of actin to cause depolymerization and Cap Z binding. Free actin subunits can then reassemble at the leading edge, extending the cytoplasm of the migrating cell.

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34
Q

What are the 5 types of actin arrays in cells?

A
  1. Stress fibers/focal contacts: contractile bundles of anti-parallel actin; link to extracellular matrix via integrins.
  2. Cell cortex: actin gel-like network beneath plasma membrane
  3. Filopodia and microvilli: tight parallel bundles of actin
  4. Lamellipodia: gel-like network of actin
  5. Adherens junctions: link to other cells via cadherins
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35
Q

___ determines the type of actin array generated.

A

The geometry of actin binding domains

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36
Q

What are the two types of proteins involved in actin filament cross-linking?

A
  1. Bundling proteins

2. Gel forming proteins

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37
Q

What are the two types of bundling proteins?

A

Fimbrin (monomer, parallel bundle, tight packing, prevents mysoin II entrance) and Alpha-actinin (dimer, anti-parallel contractile bundle, loose packing, allows mysoin II to enter)

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38
Q

What are the two types of gel forming proteins?

A

Spectrin (tetramer) and filamin (dimer)

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39
Q

___ activation induces polymerization and bundling.

A

Rho (protein family of GTPases)

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40
Q

What are three types of Rho, where are they found, and how are they packed?

A
  1. Cdc42: microspikes and filopodia, parallel, tightly packed
  2. Rac1: lamellipodia, membrane ruffles, gel at cell cortex
  3. Rho: stress fibers and focal contacts, anti-parallel, loosely packed
41
Q

How do actin targeted drugs such as phalloidin, cytochalasin, and latrunculin work? Are they clinically useful?

A

They interfere with or promote depolymerization and polymerization through stabilization of that which they bind to; No

42
Q

___ also target actin polymerization, inducing cell death and disrupting tight junctions.

A

Bacterial toxins

43
Q

___ binds actin filaments, reducing actin critical concentration to 0 and stabilizing existing filaments so they do not disassemble.

A

Phalloidin

44
Q

What is the actin molecular motor?

A

Myosin

45
Q

Myosins bind ___ filaments and use ___ to move in one direction.

A

Polarized; ATP hydrolysis

46
Q

Myosin II moves to the ___ end of the filament and is found in ___.

A

Positive; muscle

47
Q

What determines the polarity of movement and the cargo of myosin?

A

Structure (most are directed to the + end)

48
Q

Myosin forms a ___ of two alpha helices; at the N-terminus, there are two ___ that can bind to myosin. Ultimately, this forms ___ to which 2 actin filaments bind.

A

coiled-coil; head groups; myosin II bipolar thick filament

49
Q

In the myosin II bipolar thick filament, where are the myosin heads located?

A

Outside

50
Q

Myosin ___ on actin at a high speed.

A

Rows

51
Q

What is the myosin motor mechanism?

A

Rigor state: myosin bound, no ATP, ATP binds to myosin, which detaches, ATP hydrolysis occurs (cocked), myosin binds to actin, myosin releases ADP, the power stoke occurs.

52
Q

Is myosin attached or detached for most of the hydrolysis cycle?

A

Detached

53
Q

What disease is caused by mutations in the myosin beta heavy chains and leads to enlarged heart, cardiac arrhythmia, and sudden death in young athletes?

A

Familial hypertrophic cardiomyopathy

54
Q

What are the 3 functions of microtubules?

A
  1. Positioning of organelles
  2. Intracellular transport
  3. Cell motility (flagella and cilia)
55
Q

The Golgi and the ER are localized via ___.

A

Microtubules

56
Q

Intracellular transport via microtubules occurs in what three instances?

A
  1. Mitotic spindles
  2. Vesicular transport on ER via MT tracks
  3. Organelles move bidirectionally along microtubules
57
Q

What is the soluble subunit of microtubules?

A

Alpha-tubulin and beta-tubulin heterodimers

58
Q

Both alpha-tubulin and beta-tubulin can bind ___.

A

GTP

59
Q

13 ___ form the microtubule.

A

Protofilaments

60
Q

___ GTP can be hydrolyzed.

A

Beta-tubulin

61
Q

Are microtubules polar? If so, which end is more dynamic?

A

Yes; + end more dynamic

62
Q

The - end of microtubules is buried in the ___.

A

Microtubule Organizing Center (MTOC)

63
Q

MTOCs organize different types of MT arrays. What are 3 of these?

A
  1. Gamma-tubulin ring complex: embedded component of MTOC
  2. Centrosomes: spherical MTOCs, contain a pair of centrioles (help duplicate centrosomes, found near nucleus)
  3. Basal bodies: organize cilia and flagella MT (found near plasma membrane)
64
Q

MT grow from the ___ in the ___ direction.

A

Gamma-tubulin ring complex; negative to positive

65
Q

MT assembly and disassembly results from ___.

A

Nucleotide hydrolysis

66
Q

Describe the process of dynamic instability in MT.

A

Only the + end of MTs are free. The - ends are buried in centrosomes. The GTP-form favors assembly. Accidental loss of the GTP cap occurs (catastrophe). Rapid depolymerization occurs, as the GDP-form favors disassembly. Regaining the GTP cap (rescue) begins the process over again.

67
Q

Which form favors MT assembly? Disassembly?

A

T form (GTP bound); D form (GDP bound)

68
Q

___ organize MTs into astral arrays.

A

Centrosomes

69
Q

What are MAPs?

A

Microtubule Associated Proteins; filament cross-linking proteins involved in spacing and stabilizing MT.

70
Q

What are the two major types of MAPs?

A
  1. MAP2 - has a long arm

2. Tau - has a short arm

71
Q

What determines MT spacing?

A

Spacer arms in MAPs

72
Q

What protein aggregates in Alzheimer’s?

A

Tau

73
Q

What makes MT targeted drugs such as taxol, colchicine, vinblistine, and nocodazole effective cancer drugs?

A

Disrupt mitotic spindle formation selectively in rapidly growing cells.

74
Q

MT molecular motors bind MT and use ATP hydrolysis to move cargo in ___ direction(s).

A

One

75
Q

What are the two types of MT molecular motors?

A

Kinesin and dyneins

76
Q

What do kinesin and its related proteins (KRPs) do?

A

Move cargo to the + end

77
Q

What do dyneins do?

A

Move cargo to the - end

78
Q

Kinesin ___ hand-over-hand in a processive fashion on the MT as a ___.

A

Walks; dimer

79
Q

Kinesin is in contact with the MT ___% of the time.

A

50

80
Q

Kinesin moves cargo slowly but ___.

A

Reliably

81
Q

What are two specialized MT-based structure known as axonemal dyneins?

A

Flagella and cilia

82
Q

Where are flagella found and what type of motion do they utilize?

A

Protozoa and sperm, wave-like motion

83
Q

Where are cilia found and what type of motion do they utilize?

A

Respiratory epithelium, whip-like motion

84
Q

What is an axoneme?

A

9 doublets + 2 singlets, configuration of MT core inside cilia and flagella; also contains many connector proteins

85
Q

What are basal bodies?

A

MTOCs that anchor cilia and flagella at the cell surface, similar to a centriole, always by plasma membrane

86
Q

Basal bodies involve ___ MT triplets.

A

9

87
Q

What is Kartagener’s syndrome?

A

Primary ciliary dyskinesia (defect in ciliary dynein), leads to infertility in both sexes, respiratory issues (sinus infections), and situs inversus (organ position inverted)

88
Q

What are the 4 functions of intermediate filaments (IF)?

A
  1. Mechanical strength - give cells and tissues their integrity.
  2. Cell adhesion - promote cell-cell adhesion at the desmosome and cell-matrix adhesion at hemidesmosome
  3. Neuron axon diameter and strength
  4. Nuclear lamins - contribute to nucleus mechaniacal integrity
89
Q

Mutant IF causes ___.

A

Epidermolysis Bullosa simplex (EBS)

90
Q

Laminopathies are associated with mutations in ___.

A

Lamin A

91
Q

What causes the high physical strength of IF?

A

Staggered and lateral subunit interactions

92
Q

Are IFs polar?

A

No - they are symmetrical

93
Q

What is the soluble subunit of IFs?

A

Staggered tetramer of 2 coiled-coil dimers

94
Q

___ tetramers associate laterally to form an IF.

A

8

95
Q

In IF cross-linking, the ___ domain binds to neighboring filaments.

A

C-terminal

96
Q

What are tonofilaments?

A

Bundled keratin IFs

97
Q

Accessory proteins organize IFs. What are two accessory proteins?

A
  1. Filaggrin - bundles keratin IF

2. Plectin - bundles vimentin IF, binds to actin filaments, motor ptoeins, plasma membrane

98
Q

IF proteins involve a heterogenous gene family with ___+ members.

A

70

99
Q

IF have ___-specific expression.

A

Tissue

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