The drug taxol, extracted from the bark of yew trees, consists of the opposite effect of the drug colchicine, an alkaloid from autumn crocus. Taxol binds tightly to microtubules and stabilizes them. Whenever taxol is added to the cells, it causes much of the free tubulin to assemble into microtubules. In contrast, colchicine prevents microtubule formation. Taxol is just as disruptive to dividing cells as colchicine, and both are employed as anticancer drugs. Based on your knowledge of microtubule dynamics, propose why both drugs are toxic to dividing cells in spite of their opposite actions.