Term
| What factors are necessary for actin growth? How do these requirements differ between the (+) and (-) ends? |
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Definition
1) 46kD Cytoplasmic Globular (G) actin
- 1mM required for (+) end while 8mM required for (-) end.
- This contributes to the fact that the (+) end extends 5x faster.
2) K and Mg
** Addition continues in concentration dependent manner in cytoplasm until association= disassociation** |
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Term
| Why effect might defects in ADF/cofilin binding have on cytoskeletal polymerization? |
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Definition
Remember the mechanism of actin polymerization.
MOST IMPORTANT:
Wasp activates Arp23 Complex
Arp23 complex initiates branches
Cofillin chops up actin
Profilin recycles ATP-actin to start new branches
1) Wasp is activated by GTPases and PIP2
2) Wasp activates ARP 2/3, enabling branch extension
3) Addition continues until cap protein added
4) ADF/Cofilin binds to actin polymer and chops it up
5) Profilin competes with ADF/Cofilin for ADP-actin, speeds switch with ATP, and holds ATP-actin in the soluble pool for additional branching
6) Profilin releases from ATP actin and actin can polymerize again (regenerates ATP-actin for another round).
So, a defect in ADF/cofilin binding would prevent the "chopping" up of the growing actin filament and would also effect competition with Profilin |
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Term
1) How do actin filaments interact with the plasma membrane?
2) What functions do these interactions perform? |
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Definition
1) All Art Ventures Take Positive Motivation (AAVTPM)
Actin -alpha-actinin-vinculin-talin-PM through receptors (fibronectin)
** Spectrin and dystrophin are similar to alpha actinin**
2)
-longitudinal stress at ends of muscle fibers and tension generation across intercalated disks
- microvillus border of epithelial cells in the trachea and gut (anchored to fodrin (spectrin-like) and bundled into microvillus with villin and fimbrin. Recall, VILLIN is calcium-sensitive, so when calcium gets elevated such as in diarrhea, actin is severed and brush border is disassembled). |
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Term
| Describe the basic structure of myosin. |
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Definition
1) 2 globular head regions (N terminus) with 2 regulatory light chains attached to each.
2) Tail varies between different molecules except in muscle (myosin II), where the tail is alpha helical and 130nm long.
3) Interleaves with actin filaments linked together by alpha actinin at the Z-line of the sarcomere (linked together to form myofibrils). |
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Term
| What are the components of sarcomeres? |
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Definition
1) Topomyosin wound around actin, adding rigidity
2) Alpha actinin binds actin filaments across Z-line
3) Desmin, plectin and nestin give dynamic structure
4) Nebulin runs along side actin polymer adding rigidity
5) Titrin acts as spring, linking Z-line to M-line |
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Term
1) What is a fundamental difference in the way that microtubules and actin microfilaments operate?
2) What about in terms of how they are structured? |
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Definition
1) Microtubules each function as individual entities (tubulin is much more dynamic than actin, polymerizing and depolymerizing rapidly).
Actin microfilaments function in bundles and networks.
2) Microtubules are composed of heterodimers (52kD alpha/beta tubulin). They assemble into 13 protoliament repeat dimers of 8nm in length.
Actin microfilaments are composed of monomers
3) Much more actin around then tubulin |
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Term
| How do microtubules grow? |
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Definition
-(+) end grows 2x faster than (-) (remember, 5x faster in actin)
- (+) depolymerizes 2x as fast as well.
1) Tubulin GTP-bound dimers add to microtubule without hydrolyzing GTP
2) Once bound, GTP is hydrolyzed and GDP-bound tubulin depolymerizes very rapidly (100x as fast as GTP)
3) If GTP tubulin is not added continually, the hydrolyzed cap will be exposed and microtubule will depolymerize very rapidly
10 minute half-life means microtubules are made on the fly! |
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Term
| What would happen to microtubule populations if GTP-bound tubulin dimers could not hydrolyze GTP? |
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Definition
They would lose motility!
Remember, GTP-hydrolysis drives rapid depolymerization of GDP-bound tubulin dimers. |
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Term
| Where does microtubule growth originate from? What if this element is missing? |
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Definition
-Mitochondrial Organizing center (MTOC)- centriole in nucleated cells.
- If MTOC is missing, need a primer to start addition (slower)
NO ADDITION AT (-) END |
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Term
| How is microtubule stabilization at (+) end achieved? |
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Definition
1) Acetylation and de-tyrosination at alpha subunit (stabilize flagella)
2) MAPS and Tau speed up polymerization by forming nucleation centers. |
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Term
| What structures involve "9 +2" microtubule organization? |
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Definition
Microtubules forming flagella/cilia (sperm and in trachea to waft contaminants from lungs)
Dynein "cocks back" anchored cilia to increase potential energy that can be released to generate locomotion |
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Term
| How does Dynein and Kinesin act as a molecular motors? |
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Definition
Dynein binds (+) end and moves (-) end.
Drives (-) end movement in structures such as GOlgi and RER
Kinesin drives (+) end (Drives vesicles that move away from nucleus)
Dynein is larger and faster than Kinesin. |
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Term
| What three fibers do centrioles send out as they move to opposite cellular poles in mitosis? |
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Definition
1) Astral (orientation)
2) Polar (spacing b/w centrioles)
3) Kinetochore (drive chromosomes) |
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Term
| What are major differences b/w intermediate filaments and both actin and tubulin? |
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Definition
1) Very stable (require denaturing agents to depolymerize)
2) Differ according to cell type |
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Term
| What is the basic structure of intermediate filaments? |
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Definition
1) Subunit specific N-terminus
2) Rod domain
3) Subunit specific C-terminus
- subunits polymerize into touch fibrous rod |
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Term
| What are the 4 types of intermediate filaments? |
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Definition
1) Keratins in skin, hair and nails
2) Vimentin (mesencyme), Desmin (muscle), GFP (glial cells)
3) Neurofilament proteins (neurons)
4) Nuclear Lamins |
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Term
| What is the function of intermediate filaments in muscle? |
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Definition
- Desmin ensures lateral opposition of sarcomeres at Z-line
- Cytoskeletal proteins such as Titin (links myosin at Z-line) and Nebullin (orders actin) also play roles |
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Term
| What is the function of intermediate filaments in epithelia? |
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Definition
| - Keratins act as insertion point to stabilize microvillus structure |
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Term
| How is Villin "bifunctional"? |
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Definition
1) When Ca is normal, Villin acts as a actin-bundler
2) When Ca is high (diarrhea), Villin chops up actin and disassembles brush border |
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Term
| How does Myosin 1 differ form Myosin 2 (functionally)? |
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Definition
Myosin 1 moves vesicles in an ATP-dependent, rapid process.
Myosin 2 is in muscle cells and is critical for shortening of actin filaments at Z line. |
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Term
True:False
The activity of molecular motors is critical for chromosome separate at the metaphase plate during mitosis. |
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Definition
FALSE.
Unknown mechanism, but it DOES NOT require motors. |
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Term
| What is "dynamic instability" of microtubules and how is it critical in mitosis? |
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Definition
Rapid (10 min half-life) polymerization and depolymerization
Kinetochore can only form after microtubules "fish" for chromosomes using this dynamic instability to hook onto them. |
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