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Review Questions
Diagram the structure of a kinesin-5 homotetramer. Now place this structure between one pair of MTs that is parallel and another pair that is antiparallel. Now sketch the situation at later times, showing what the action of the motor domain of this enzyme will do to the relative positions of the motor and the MTs. Given what you know about kinesin-5, explain why its inhibition blocks the formation of a bi-polar spindle. The localization of Ase1 and the phenotype of its deletion imply that this protein binds to anti-parallel MTs. What would you expect for the organization of a protein that has this property? Diagram the process of MT flux, showing where tubulin subunits must add and fall off of the spindle MTs during MT movement. Use the above diagram to develop your own model for anaphase B, the elongation of a spindle. Now extend this diagram to include the idea of a pull, exerted on astral MTs by the cell’s cortex. Draw a diagram of a cell in which a chromosome is being manipulated, as in the experiment by Nicklas. Recall that the cell’s membrane is tough and doesn’t break, so the needle is always outside the cell, even when it is pushing on the chromosome. Rieder’s experiment that used laser microsurgery to cut a chromosome’s arms away from its kinetochores showed the existence of forces that push objects away from the spindle pole. In these same cells, what would you predict for the metaphase position of a chromosome that is associated with only one spindle pole?
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