AP Biology/How Cells Divide

Eukaryotic cells divide through a process called mitosis followed by cytokinesis.

Mitosis

Mitosis in itself is the division of the nucleus inside the cell. However, once the nucleus divides, the whole cell divides shortly afterwards, known as cytokinesis.

The stages of mitosis are as follows:

Interphase

Interphase is considered by most to be a resting phase. It consists of G1, S, and G2.

Prophase

Just prior to mitosis, the pair of centrioles duplicates. During prophase, the two pairs of centrioles migrate to opposite poles. Centrioles form spindle fibers, which become microtubules and eventually attach to the centromeres. Fibers, known as asters, radiate from the centrioles outward.

Metaphase

The spindle fibers enter the nuclear region, extend from the centrioles to the centromere, and attach at a point known as the kinetechore. Once the spindle fibers are attached, they align the centromeres along the equatorial region of the nucleus known as the metaphase plate, so that the arms of the chromosomes point towards the poles of the cell.

Anaphase

The centromere divides and the two chromatids separate from each other, forming two identical daughter chromosomes. The spindle fibers attach to the centromere and pull the newly-divided chromosomes towards the poles and away from the metaphase plate. The spindle fibers appear to move, but in fact, the microtubules are continuously formed at one end of the spindle fiber and then disassembled at the other.

Telophase

After the chromosomes reach the poles, a nuclear membrane forms around each set of daughter nuclei and the chromosomes uncoil and elongate, once again becoming invisible. The spindle fibers break down and disappear. In animal cells, a cleavage furrow, an indentation in the cell membrane, begins to develop between the daughter cells. This marks the end of mitosis.