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BMS2.14 Cytoskeleton I > Cytoskeleton 1 > Flashcards

Cytoskeleton 1 Flashcards

1
Q

The cytoskeleton is involved with:

A
  • cell shape
  • cell’s ability to migrate
  • formation of mitotic spindle
  • chromosome separation during anaphase
  • intracellular transport
  • exo/endocytosis
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2
Q

What are the three cytoskeletal components?

A
  • actin (5-9nm)
  • intermediate filaments (10nm)
  • microtubules (25nm)

all of these components can interact with one another

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3
Q

Cytoskeletal structures are:

A
  • non-covalent polymers of smaller protein subunits.
  • dynamic and adaptable.
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4
Q

What regulates the sites and states of cytoskeleton assembly?

A

accessory proteins in response to intra- and extracellular signals

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5
Q

Intermediate filaments roles:

A
  • major components of nuclear (lamins) and cell structure
  • roles in:
    • mechanical support (skin)
    • cell migration and movement
    • cytoarchitecture
    • signaling
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6
Q

Intermediate filaments protects cells from:

A
  • mechanical stress; they are stress absorbers
    • viscoelastic filaments within cells and at junctions between cells and with extracellular matrix.
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7
Q

Skin, hair, and nails are all composed of what types of filaments?

A

intermediate filaments

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8
Q

Keratins, nuclear lamins, and neurofilaments are all what types of filaments?

A

intermediate filaments

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9
Q

Basic structure of intermediate filaments:

A
  • two-chained coiled coil that assembles to form tetramer.
    • tetramer forms higher order assemblies, 10 nm filament.
  • N-terminal and C-terminal ends are globular; coiled coil region interrupted by linker domains.
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10
Q

Steps in formation of an intermediate filament:

A
  1. alpha-helical region in a monomer forms coiled-coil dimer with another alpha-helical region of a monomer.
  2. coiled-coil dimer forms staggered tetramer with another coiled-coil dimer.
  3. two staggered tetramers are packed together.
  4. eight-tetramers twist into a rope-like filament.
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11
Q

Intermediate filaments assemble as _____ tetramers:

A
  • antiparallel
    • non-polar filaments
      • reason why there are no motors
      • not involved in directional movement
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12
Q

What two filaments are polar structures?

A

actin and microtubules

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13
Q

Actin filaments (F-actin) are polymers of:

A
  • globular protein actin (G-actin) that contains a bound nucleotide (ATP or ADP).
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14
Q

General characteristics of actin filaments:

A
  • polymers of actin
  • polar
  • helical
  • plus-end (fast growing) and minus-end (slow-growing)
  • only two actin genes in genome
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15
Q

Plus end and minus end of actin filaments:

A
  • have nothing to do with charge; names based on assembly kinetics:
    • plus end = fast-growing
    • minus end = slow-growing
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16
Q

What is the rate-limiting step of actin polymerization?

A
  • nucleation
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17
Q

Actin monomers have ATP attached. What is this ATP used for?

A
  • NOT required for polymerization
  • the bound ATP influences the stability of the filament ends.
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18
Q

What kind of proteins regulate actin polymerization and growth?

A
  • capping proteins
    • (actin filament can only grow one way)
  • severing proteins
    • (cuts actin filaments)
  • cross-linking proteins
    • (attaches actin filaments)
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19
Q

Stability of actin filaments and microtubules is determined by:

A
  • the nucleotide at the plus-end of the filaments
20
Q

Actin filament and microtubule parallels:

A
  • nucleation-polymerization from monomeric proteins
  • polar structures
  • grow from plus-ends
  • plus-end determines stability
  • regulated by binding proteins
21
Q

Are actin and microtubule structures related?

A

no

22
Q

The monomer building block of microtubules is:

A
  • tubulin heterodimer.
    • two subunits:
      • alpha-tubulin
      • beta-tubulin
23
Q

Basic microtubule structure:

A
  • Polymers of alpha/beta-tubulin arranged in tubules with 13 protofilaments.
  • POLAR
24
Q

Microtubules are used for:

A
  • vesicular and organelle transport
  • formation of mitotic spindle, cilia and flagella
  • formation of centriole and basal bodies
25
Q

Primary cilium:

A
  • a non-motile cilia composed of microtubules
  • one per cell
  • sensory organelles involved in signalling pathways
  • NO DYNEIN (the motor of cilia)
26
Q

Centrosome:

A
  • microtubule organizing center
    • forms around two centrioles
  • nearly all microtubules project from centrosomes
    • plus-end projects to cell periphery
    • minus-end at centrosomes
    • POLARITY
27
Q

Centrioles are duplicated during what phase of the cell cycle?

A

S-phase

28
Q

Formation of the mitotic spindle and chromosome separation is dependent on:

A

microtubule polarity

29
Q

How is polarity formed in actin filaments and microtubules?

A
  • minus end addition is slow
    • GTP/ATP hydrolyzed to GDP/ADP
  • plus end addition is fst
    • GTP/ATP hydrolysis cannot keep up
    • GTP/ATP remains on plus-end cap
30
Q

The nucleotide at the plus end affects microtubule growth and stability. How so?

A
  • plus end GTP-cap stabilizes the microtubule.
    • microtubule grows
  • loss of GTP-cap destabilizes microtubule.
    • microtubule collapses
  • regain of GTP-cap stabilizes microtubule.
    • microtubule growth recurs
31
Q

Mictroubule catastrophe and rescue:

A
  • catastrophe = loss of GTP-cap on plus end and microtubule collapse
    • when GTP-hydrolysis catches up to the growing end.
  • rescue = regain of GTP-cap on plus end and microtubule regrowth.
32
Q

Microtubule associated proteins (MAPs):

A
  • Regulate state of microtubule assembly
  • Stabilize or destabilize plus or minus end
  • Bind to the side: stabilize by side binding or bundle formation
  • Sever
33
Q

gamma-tubulin ring complex location and function:

A
  • found at the minus end of microtubules at the centrosome
  • nucleates minus end
  • stabilizes minus end
34
Q

Tau:

A
  • a microtubule side-binding protein
  • Alzheimer’s disease = tau in neurofibrillary tangles/aggregates.
35
Q

+tip proteins:

A

INHIBIT MICROTUBULE CATASTROPHE

  • bind to and track with the plus end of a growing microtubule.
    • stay with the plus end as it is growing.
  • interact with actin skeleton
  • transport materials to cell periphery
  • connects to kinetochore in mitosis
36
Q

Phalloidin:

A
  • actin filament toxin
    • binds and stabilizes actin filaments
  • found in death angel mushroom
37
Q

Colchicine:

A
  • microtubule toxin
    • deploymerizes microtubules
38
Q

Taxol:

A
  • microtubule toxin
    • binds and stabilizes microtubules
  • widely used as an anti-cancer drug
39
Q

Cell migration is involved in:

A
  • pathfinding and targeting of neurons
  • chemotaxis (neutrophils to infection)
  • tissue formation, repair, remodeling (wounds)
  • cancer metastasis
40
Q

Cellular movement and intracellular transport can be driven by:

A
  • both polymerization and motors
41
Q

Neutrophils chase bacteria during infection via:

A
  • chemotaxis
    • actin polymerization at the leading edge
    • myosin-II dependent contractions of the tail
42
Q

How does actin polymerization alone provide the force for cell movement?

A
  • actin filaments push against cell membrane:
    • elongation/polymerization at plus/barbed end
    • nucleation of more actin filaments
    • formation of branches
43
Q

Arp2/3 complex:

A
  • Nucleates filaments from the sides of actin filaments, making complex branched structures.
    • branches grow at plus end and can push against cell membrane.
    • involved in cell movement
44
Q

Arp2/3 is activated by:

A
  • Downstream rho family of small GTPases signaling cascades.
    • localizes activation at the cell membrane
    • catalyzes cell movement
45
Q

Arp2/3 activation is involved in actin polymerization for cell movement in what situations?

A
  • neutrophil migration to infection
  • wound healing
  • cancer metastasis
  • endocytosis
46
Q

Listeria:

A
  • food-borne pathogen
  • contains proteins homologous to Arp2/3 activating proteins
    • hijacks cell’s Arp2/3 machinery causing actin polymerization on listeria molecule tails.
    • listeria molecules protrude from one cell and infect another.

BMS2.14 Cytoskeleton I (1 decks)

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