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33 Cards in this Set
- Front
- Back
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What is the structure of microtubules?
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-13 protofilaments, all with same orientation --> Polarity
-α- and β-tubulin form heterodimers |
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Can alpha tubulin have GTP hydrolyzed?
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GTP not hydrolyzable, not exchangable
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Can beta tubulin cleave GTP?
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can cleave GTP, can exchange with free GTP
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What is the structure of a singlet microtubule?
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13 protofilaments, 25 nm outer diameter, 15 nm inner diameter, hollow tube
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What is the structure of a doublet microtubule?
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singlet microtubule with 10 protofilament tubule. Present in cilia and flagella
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What is the structure of a triplet microtubule?
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doublet microtubule plus 10 protofilament tubule. present in basal bodies and centrioles.
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How is the polarity of microtubules arranged?
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the (-) end is anchored in the microtubule organizing center, with the (+) end toward the periphery of the cell
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Where are microtubules assembled?
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from microtubule organizing centers
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What is the centrosome?
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microtubule organizing center of non-mitotic cells
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What do the spindle poles do?
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assemble the microtubules of the mitotic spindle
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What is the function of the basal body?
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assemble the microtubules of cilia and flagella
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What is the structure of a centrosome?
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-two centrioles at right angles surrounded by pericentriolar material
-made up of 9 triplet microtubules |
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How are new microtubules formed?
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gamma tubulin ring complex may form a split-washer type template to bind alpha-beta-tubulin dimers, forming a new microtubule
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What happens to microtubules if they are chilled to 4 C or lower?
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disassemble into tubulin dimers and microtubule associated proteins
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What happens to microtubules if they are warmed to 37 C or higher?
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reassemble into microtubules
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How do microtubules grow?
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-at the (+) end at steady-state
-treadmilling of microfilaments |
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How do microtubules do work?
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the energy of hydrolyzed GTP is stored as torsional energy- allowing the microtubules to do work
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What happens if a microtubule contains GTP-beta-tubulin at the (+) end?
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assembly
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What happens if a microtubule contains GDP-beta-tubulin at the (+) end?
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disassembly
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How are microtubules stabalized?
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-GTP-beta-tubulin has strong lateral interactions with GTP-beta-tubulin in other profilaments
-Tau proteins bind both sides of the microtubule and TIP proteins bind at (+) end of microtubules |
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How are GTP and GDP bound in a growing protofilament?
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A growing protofilament has GDP-beta-tubulin down its length, but is capped by GTP-beta-tubulin
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What does colchicine, podophyllotoxin, and nocodazole do?
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sequesters tubulin dimers causing depolymerization of microtubules
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What does taxol do?
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-stabilizes microtubules, preventing depolymerization which inhibits mitosis
-used to treat breast and ovarian cancer |
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What is the importance of microtubule-associated proteins?
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determine spacing of microtubules
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How are microtubules disassembled?
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Kinesin-13 family and Op18/Stathmin act at the ends of microtubules. Katanin then severs and releases anchored microtubules in microtubule organizing center
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How do organelles interact with microtubules?
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organelles move along microtubules
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What is kinesin-1?
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a class of motor proteins found in eukaryotic cells. Kinesins move along microtubule cables powered by the hydrolysis of ATP (thus kinesins are ATPases). The active movement of kinesins supports several cellular functions including mitosis, meiosis and transport of cargo such as axonal transport.
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What is the structure and function of Kinesin-1?
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-conventional
-organelle transport |
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What is the structure and function of Kinesin-2?
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-heterotrimeric
-organelle transport |
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What is the structure and function of Kinesin-5?
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-bipolar
-sliding |
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What is the structure and function of Kinesin-13?
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-Kinl
-end disassembly |
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What is the mechanism of kinesin walking?
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1) Forward motor binds beta-tubulin, releasing ADP
2) Forward head binds ATP 3) Conformational change in neck linker causes rear head to swing forward 4) New forward head releases ADP, trailing head hydrolyzes ATP and releases Pi |
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What is a cytoplasmic dynein?
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a motor protein (also called molecular motor or motor molecule) in cells which converts the chemical energy contained in ATP into the mechanical energy of movement. Dynein transports various cellular cargo by "walking" along cytoskeletal microtubules towards the minus-end of the microtubule, which is usually oriented towards the cell center. Thus, they are called "minus-end directed motors."
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