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30 Cards in this Set
- Front
- Back
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What are microtubules made of?
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A microtubule is comprised of 13 protofilaments.
α- and β-tubulin make up protofilaments. |
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What is necessary for self assembly of microtubules?
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Critical concentrations of heterodimers, GTP and physiological concentration of salts
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What is one way to measure the inherent polarity of microtubules?
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The different assembly rates of their (+) and (-) ends
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What is treadmilling? When does it occur?
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Heterodimers pass from the (+) end and fall off (-) end due to differing dis/association rates at the two ends. It occurs under equilibrium conditions in vivo.
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What is dynamic instability?
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The process in which assembly or disassembly of microtubules is regulated locally based on the fact that assembly is favored when the dimers at (+) end contain bound GTP.
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What are the five steps/stages of dynamic instability?
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1) (+) end polymerization requires GTP
2) GTP-cap helps dimerize 3) Too much dimer addition? GTP cap stabilizes microtubule 4) ↓ dimer addition, lose GTP cap → rapid depolymerization! 5) Depolymerization = fast, complete |
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What is the bipolar mitotic spindle?
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Made of microtubules and is required for chromosome segregation during mitosis.
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When are spindle microtubules formed? When do they depolymerize?
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Form in metaphase. Depolymerize at the end of cell division.
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What does taxol do?
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Taxol is an anti-cancer drug that stabilizes microtubules, preventing them from depolymerizing at the end of mitosis.
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How do microtubule anti-cancer drugs work?
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These drugs interfere with cell division by binding to tubulin and either stabilize or disrupt microtubules.
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What is the cell's principal microtubule organizing center?
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the centrosome
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What are microtubule organizing centers?
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Sites where polymerization of microtubules is organized or initiated.
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What are centrioles? Where are they found?
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Centrioles are involved in the organization of the mitotic spindle. They are found in the centrosome.
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What are basal bodies?
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Basal bodies are centrioles (mitotic spindle organizers) at the cell surface from which cilia extend
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Microtubule organizing centers (MTOCs) help establish uniform polarity of microtubules relative to other organelles how?
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The (-) end of microtubules are adjacent to MTOCs.
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What is the role of γ-tubulin (gamma tubulin)?
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It is a component of the γ-tubulin ring complex (large, multiprotein).
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What is the role of the γ-tubulin (gamma-tubulin) complex?
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Involved in initiation of polymerization of microtubules at MTOCs.
Caps the (-) end of the microtubule preventing its disassembly. |
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What are cilia and flagella? Where are they found?
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Microtubule-based organelles that are either motile organelles (cilia of respiratory tract, sperm) or sensory in function (sensory cilia of olfactory, kidney tubules, photoreceptors). They are found on the cell surface.
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What is the axoneme? What is important about it's patterning?
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The axoneme is the cytoskeletal component of the cilium or flagellum. It has a highly conserved 9 + 2 pattern of microtubules. (9 outer doubles of A & B subfibers, 2 normal centrally-located microtubules). Most sensory cilia do not have the central 2 microtubules.
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Where do axonemes arise from?
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Basal bodies consisting of a cross-linked array of 9 triplet microtubules.
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What is ciliary bending a classic model of?
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Microtubule based motility. The molecular motor is dynein, which causes relative sliding between microtubules in the axoneme. Dynein is a large protein complex that uses energy from ATP hydrolysis to move cargo along microtubules.
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What is the role microtubules play in motility?
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Microtubules serve as tracks and the motility motors dynein or kinesin move along the track. The motors hydrolyze ATP and through conformational changes in the protein are able to translocate cargo.
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What mediates motility on single cytoplasmic microtubules?
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Cytoplasmic form of dynein or by kinesin
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What can cytoplasmic dynein or kinesin associate with? What do dynein or kinesin do?
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Cytoplasmic dynein or kinesin associates with surface of organelles and they move the organelles along the microtubule.
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How do motor molecules (dynein and kinesin) move?
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Dynein and kinesin move unidirectionally on microtubules.
Dynein moves from (+) → (-). Kinesin moves from (-) → (+). |
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How do dynein and kinesin move?
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Both motors have two ATPase head domains and are thought to move along microtubules in a cross-bridge cycle.
For kinesin, a cross-bridge cycle coupled to ATP hydrolysis results in movement along the microtubules. |
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What is fast axonal transport of vesicles an example of?
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Microtubule mediated motility.
In neurons it is critical that vesicles generated through synthesis in the cell body be delivered to the synapse and that vesicular components of the synapse be returned to the cell body. Such vesicles become closely associated with microtubules by binding dynein or kinesin. |
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What is the uniform polarity of microtubules in axons?
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(-) end at cell body
(+) end at synapse |
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How is transport along axonal microtubules mediated?
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Transport toward the synapse is mediated by kinesin (anterograde).
Transport toward the cell body is mediated by dynein (retrograde). |
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How are microtubule based motors utilized in mitosis?
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(+) and (-) end directed motors play important roles in cell division through their specific association with spindle microtubules. In each case the motor head associates with an adjacent microtubule and provides force that is either (+) or (-) end directed. The motors are anchored at one end either to a microtubule or plasma membrane.
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