Nocodazole reversibly inhibits microtubule polymerization, which is essential for formation of the mitotic spindle. By treating a population of mammalian cells with nocodazole for a time and then washing it out of the medium, it is possible to synchronize the cell population so that they are all in the same phase of growth. In the presence of nocodazole, where in the cell cycle do the cells accumulate? What mechanism of the cell is stopping their progression through the cell cycle?