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BMS-II > Cytoskeleton I > Flashcards

Cytoskeleton I Flashcards

1
Q

What are the roles of cytoskeleton?

A
  1. Establishment of cellular polarity (not necess +/- charge mind you)
  2. Directional migration
  3. Formation of bipolar mitotic/meiotic spindle
  4. Chromosome segregation
  5. Cytokinesis

Also intracellular transport, exocytosis, endocytosis

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2
Q

What are the three cytoskeletal components & their sizes?

A

Actin - 5-9mm (10-15% protein in cell)

INtermediate filaments - 10nm

Microtubules - 25nm

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3
Q

What cytoskeleton component composes microvilli projections? Where do they end?

A

Actin filaments. Come to a terminal web of actin

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4
Q

Where are intermediate filaments located in epithelial cells?

A

Between desmosomes and basal lamina.

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5
Q

Where are microtubules located in epithelium? What is the polarity of these?

A

Connecting apical surface to of cell to bottom of cell.

(Minus end (-)) is at apical surface
(Plus end (+)) is at basal surface

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6
Q

How are larger cytoskeletal structures assembled?

A

Smaller protein subunits

(Non-covalent polymers)
Dynamic

Accessory proteins regulate sites and state of assembly

ADAPTABLE (i.e. Source of something like a nutrient source; dissasembly of filaments and rapid diffusion of subunits; then reassembly at new site)

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7
Q

What are known as the ‘tendons of the cell’?

A

Intermediate filaments (int. In size betwn actin and microtubules; more stable)

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8
Q

What are intermediate filaments function?

A

MAJOR components of cytoskeleton and nuclear boundary and functional organization of cellular architecture

Protection from mechanical stress, stress absorbers
(Viscoelastic filaments w/in cell and at junctions betwn cells and with ECM)

Signaling and controlling gene regulatory networks

No known motors

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9
Q

Where are int. Filaments found in the cell?

A

Surround nucleus and extend to cell periphery
Cell-cell & cell-ecm junctions

Controlled thru phosphorylation

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10
Q

What is basic structure of int filaments?

A

Two-chained coiled coil that assembles to form tetramer.

Tetramer forms higher order assemblies (10nm filament)

N-term and C-term ends globular.

Coiled coil regoin interrupted by linker domains

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11
Q

How do int. Filaments assemble? Is the structure polar?

A

Antiparallel tetramers.

Overall structure is not polar (in contrast to actin/microtubules)

Int. filaments only exist as dimers (in an antiparallel fashion)
They dimerize again to form an anti-parallel staggered tetramer.

They dimerize again to form a ropelike int. Filament(10nm thick)

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12
Q

What are actin filaments? (F-actin)

A

Polymers of globular protein (g-actin)contains bound nucleotide (ATP/ADP)

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13
Q

Is f-actin polar?

A

YES, they differ in structure and dynamics.

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14
Q

What are the characteristics of the plus end? MInus end?
?
What is shape of filament and how are they modified?

A

Plus/barbed end -> faster growing end

Minus/pointed end is slower growing

Filament is helical and Actin binding proteins can modify filament dynamics and higer order assemblies

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15
Q

How are polymers of alpha/beta tubulin arranged into tubules?

What is the mictotubule subunit?

A

13 protofilaments.
Bound GDP/GTP

Polar structures

(Tubulin heterodimer = microtubule subunit)

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16
Q

How are microtubules and actin filaments similar?

A
  • Assembly from globular proteins by a condensation /polymerization mechanism to form polar structure
  • Monomer addition preferred at ‘plus end’
  • Nucleotide hydrolysis lags behind polymerization leaving an ATp or GTP cap at growing end
  • NRG of hydrolysis not required for polymerization
  • Nucleotide at plus end determines stability
  • Dynamics and state of structure can be determined by actin/microtubular binding protein.

THESE STRUCTURES ARE UNRELATED

17
Q

At what side is the rate of elongation faster?

A

“Barbed”/plus end.

Nucleation is rate limiting.

ATP-actin is preferentially added to barbed end

ATP hydrolysis not required for polymerization. Bound nucleotide influences stability of the ends and interactions with other proteins.

Actin filament has ADP-actin except for the extreme barbed end.

18
Q

What state are soluble subunits in?

A

T form.

19
Q

What is the step to take place after polymerization of actin-filaments and mictrotubules?

A

Hydrolysis of NTP->NDP
Pi release takes place after polymerization

Plus end (+) ->hydrolysis lags behind

Minus end (-) ->Hydrolysis catches up

20
Q

Are microtubules generally stable?

A

No, there is dynamic instability

Nucleotide present at plus (+) end affects mictotubule growth and stability

GTP-tubulin cap stabilizes the plus (rescue)

GDP-tubulin destabilizes resulting in rapid depolymerization (catastrophe)

21
Q

What determines the state and dynamics of actin?

A

Actin binding proteins

22
Q

Why are tubulin and microtubule structure important to the cell?

A

Important for vesicular and organelle transport.

Form the mitotic spindle

Cilia and Flagella

Centriole and basal bodies

23
Q

What is a primary cilium in a cell?

A

Non-motile

Usually one per cell

Sensory organelles

Central player in development signaling pathways

24
Q

What is structural difference from motile and non-motile cilia?

A

No inner doublet

No arms

25
Q

What is the centrosome?

A

Microtubule organizing center.

Organized around a pair of centrioles.

  • > centrioles surrounded by pericentriolar material;>100 proteins
  • ->contains gammatubulin ring that nucleates 13 protofilaments of microtubules and caps the (minus/-) ends.

Consequence: _plus end oriented towards cell periphery.

26
Q

When do centrioles duplicate?

A

Beginning of S phase mitosis

27
Q

What are MAPs responsible for? Microtubules associated proteinsk

A

Regulate state of microtubule assembly
(Both stabilize/destabilize plus or minus end)

Bind to side (stabilize by side binding or bundle formation)

Sever

28
Q

What is a MAP that is implicated in Alzheimer’s diz?

A

Tau (neurofibrillary tangles).

Binds to side and makes structure very bulky

29
Q

What proteins inhibit catastrophes in microtubules? What does this allow?

A

+ tip proteins. Allows microtubules to reach the cell periphery.

Communication and connection with the cell cortex.

  • > transport materials to cortex
  • > interaction with actin cytoskeleton.

Capture chromosomes during mitosis: association with kinetochore.

30
Q

What are some toxins that interfere with microtubule/actin polymerization?

A
  1. Phalloidin -> binds and stabilizes actin filaments. Death angel mushroom
  2. Colchicine - depolymerizes microtubules. (Autumn crocus)
3. Taxol - binds and stabilizes microtubules. 
Pacific yew (natural)
Used widely as an anticancer drug
31
Q

How do neutrophils track down bacteria?

A

Chemotaxis *involves actin polymerization”

& myosin-II dependent on contractions of tail

32
Q

What is role of dynamic actin filaments in cellular function?

A

Actin polymerization alone can drive cell migration.

Certain bacteria can hijack this machinery.

33
Q

How is actin polymerization enough to force movement?

A

Needs lots of growing ends to push against the plasma membrane.

  • > Nucleate more actin filaments
  • > sever existing filaments to creat more barbed ends
  • > Form branches from existing actin filaments

Arp2/3 (complex of 7 proteins)
-> nucleates filaments from sides of actin filaments making complex branched structures

34
Q

What regulates dendritic nucleation?

A

Rho-dependent signaling cascade (rac is a subclass of rho)

Arp 2/3 is downstream of rho family of gtpases.

Localizes activation at the cell membrane, leading edge, site of protrusion of lamellipodium .

35
Q

What is Arp2/3 dependent polymerization involved in?

A
  1. Neutrophil migration to sites of infection
  2. Wound healing
  3. Invasion of metastatic cancer cells
  4. Certain bacterial infections
  5. Clathrin-dependent endocytosis
  6. Et al
36
Q

How does listeria monocytogenes infect?

A

Infects intestinal epithelium and hijacks ARP 2/3 dependent actin polymerization machinery

Protein is homologous to WASP/Scar on the bacterial surface activAtes Arp2/3

Actin filaments polymerize forms a comet that propels the bacteria thru the cytoplas.

BMS-II (9 decks)

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