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
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
3
Q
Cytoskeletal structures are:
A
- non-covalent polymers of smaller protein subunits.
- dynamic and adaptable.
4
Q
What regulates the sites and states of cytoskeleton assembly?
A
accessory proteins in response to intra- and extracellular signals
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
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.
7
Q
Skin, hair, and nails are all composed of what types of filaments?
A
intermediate filaments
8
Q
Keratins, nuclear lamins, and neurofilaments are all what types of filaments?
A
intermediate filaments
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.
10
Q
Steps in formation of an intermediate filament:
A
- alpha-helical region in a monomer forms coiled-coil dimer with another alpha-helical region of a monomer.
- coiled-coil dimer forms staggered tetramer with another coiled-coil dimer.
- two staggered tetramers are packed together.
- eight-tetramers twist into a rope-like filament.
11
Q
Intermediate filaments assemble as _____ tetramers:
A
- antiparallel
- non-polar filaments
- reason why there are no motors
- not involved in directional movement
- non-polar filaments
12
Q
What two filaments are polar structures?
A
actin and microtubules
13
Q
Actin filaments (F-actin) are polymers of:
A
- globular protein actin (G-actin) that contains a bound nucleotide (ATP or ADP).
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
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
16
Q
What is the rate-limiting step of actin polymerization?
A
- nucleation
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.
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)
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
- two subunits:
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
Primary cilium:
* a non-motile cilia composed of microtubules
* one per cell
* sensory organelles involved in signalling pathways
* **_NO DYNEIN (the motor of cilia)_**
26
Centrosome:
* 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
Centrioles are duplicated during what phase of the cell cycle?
S-phase
28
Formation of the mitotic spindle and chromosome separation is dependent on:
microtubule polarity
29
How is polarity formed in actin filaments and microtubules?
* 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
The nucleotide at the plus end affects microtubule growth and stability. How so?
* 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
Mictroubule catastrophe and rescue:
* **_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
Microtubule associated proteins (MAPs):
* 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
gamma-tubulin ring complex location and function:
* found at the minus end of microtubules at the centrosome
* nucleates minus end
* stabilizes minus end
34
Tau:
* a microtubule side-binding protein
* Alzheimer’s disease = tau in neurofibrillary tangles/aggregates.
35
+tip proteins:
**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
Phalloidin:
* actin filament toxin
* binds and stabilizes actin filaments
* found in death angel mushroom
37
Colchicine:
* microtubule toxin
* deploymerizes microtubules
38
Taxol:
* microtubule toxin
* binds and stabilizes microtubules
* widely used as an anti-cancer drug
39
Cell migration is involved in:
* pathfinding and targeting of neurons
* chemotaxis (neutrophils to infection)
* tissue formation, repair, remodeling (wounds)
* cancer metastasis
40
Cellular movement and intracellular transport can be driven by:
* both polymerization and motors
41
Neutrophils chase bacteria during infection via:
* chemotaxis
* actin polymerization at the leading edge
* myosin-II dependent contractions of the tail
42
How does actin polymerization alone provide the force for cell movement?
* actin filaments push against cell membrane:
* elongation/polymerization at plus/barbed end
* nucleation of more actin filaments
* formation of branches
43
Arp2/3 complex:
* 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
Arp2/3 is activated by:
* Downstream rho family of small GTPases signaling cascades.
* localizes activation at the cell membrane
* catalyzes cell movement
45
Arp2/3 activation is involved in actin polymerization for cell movement in what situations?
* neutrophil migration to infection
* wound healing
* cancer metastasis
* endocytosis
46
Listeria:
* 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.
