PS7KEY - Professor Hinck Bio 110, Fall, problem set 7 1)...

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Professor Hinck Bio 110, Fall, problem set 7 1) Dynamic instability causes microtubules either to grow of to shrink rapidly. Consider an individual microtubule that is in its shrinking phase. A) What must happen at the end of the microtubule in order for it to stop shrinking and start growing? B) How would an increase in the tubulin concentration affect this switch from shrinking to growing? C) What would happen if GDP, but no GTP, were present in the solution? D) What would happen if the solution contained an analog of GTP that could not be hydrolyzed? ANS: A. The microtubule is shrinking because it has lost its GTP cap; that is, the tubulin subunits at its end are all in their GDP-bound form. GTP-loaded tubulin subunits from solution will still add to this end, but they will be short- lived—either because they hydrolyze their GTP or because they fall off as the microtubule rim around them disassembles. If enough GTP-loaded subunits are added quickly enough to cover up the GDP-containing tubulin subunits at the microtubule end, then a new GTP cap can form and regrowth will be favored. B. The rate of addition of GTP-tubulin will be greater at higher tubulin concentrations. The frequency with which shrinking microtubules switch to the
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This note was uploaded on 03/28/2010 for the course MCD BIO 110 taught by Professor Hinck during the Fall '09 term at UCSC.

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PS7KEY - Professor Hinck Bio 110, Fall, problem set 7 1)...

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