Spindle fibers position and move chromosomes during mitosis, while centrioles aid in organizing the movements of microtubules. Centrioles also help arrange the nucleus and organelles of a cell.
During metaphase in a cell, pairs of chromosomes line up along the center of the cell. Special microtubules called spindle fibers attach to chromosomes to enable this arrangement. The spindle fibers form at opposites sides, or poles, of the cell and extend towards the middle. During anaphase, spindle fibers pull chromosomes to opposite poles in preparation for the creation of two new cells. Some spindle fibers never attach to chromosomes and, instead, work to lengthen the cell.
Centrioles are important in the organization of microtubules, including spindle fibers. Centrioles do not create the fibers themselves, but instead direct the positioning of the spindle. Centrioles also play an important role in cellular organization. Centrioles organize cytoplasmic microtubules that adjust the position of other organelles, including the nucleus. This is vital to mitosis, as it ensures that each new cell has the requisite number of organelles.
Cells possess two centrioles until ready to divide. At this time, a new centriole forms to one side of each original centriole. These centrioles maintain their attachment until mitosis begins.