An important organelle in the division of animal cells is the centrosome. The centrosome is the microtubule generating and organizing center of the cell. Microtubules form the support structure, or cytoskeleton, of all cells. During cell division, or mitosis, microtubules form the spindle fibers that separate chromosomes.
Centrosomes sit near the nucleus of a cell and consist of a pair of centrioles. During prophase, the first stage of mitosis, the centrioles separate and begin to migrate to opposite sides of the nucleus, forming spindle fibers as they go. At the same time, the membrane surrounding the cell’s nucleus dissolves, exposing the cell’s genetic material – the chromosomes. Each half of a chromosome, called a chromatid, becomes attached to a spindle fiber.
The next stage of mitosis is metaphase. During metaphase, the centrioles complete their migration and chromosomes align at the center of the the cell.
Anaphase involves the shortening of the spindle fibers. Shortening spindle fibers put stress on the chromosomes, causing them to fully separate into their two chromatid halves. The spindles pull the chromatids toward opposite sides of the cell. This means that each daughter cell that forms during a mitosis event gets its own pair of chromatids.
Mitosis ends with telophase. Now the chromosomes are at opposite poles of the cell, and a new nucleus forms around each set. The cell is pinched in half by more microtubules, and cell division is complete.