Mitosis

There are five main stages to mitosis (cell division). The first stage is called interphase. In this phase there is a non dividing cell. The nucleus of the cell is filled with chromatin (fine network of threads). There are three parts to interphase. The first part, G1, is the growth stage, S is where DNA replication occurs, and G2 is where the cell gets ready for mitosis and the organelles double. Then next stage is called prophase. The chromatin threads start to thicken and condense into chromosomes. Each chromosome is made up of two chromatids joined at the centromere. As this stage or phase continues, the chromatids shorten and thicken. The nuclear envelope starts to disappear.  The first sign of a spindle appears in the cytoplasm, and the spindle apparatus is made up of microtubules. The microtubules pull the chromosomes toward the poles of the spindle where two daughter nuclei will form. The nest phase is called prometaphase. Here, the nucleus membrane breaks apart into numerous "membrane vesicles" and the chromosomes inside form protein structures called kinetochores. The centrioles begin to move apart as well. The next phase is metaphase. Here the chromosomes move to the center of the spindle and the centromere attaches to the spindle. The centromeres of all the chromosomes lie at the same level of the spindle, the metaphase plate. The next phase is called anaphase. Here the centromere regions of each pair of chromatids separate and are moved by spindle fibers toward opposite poles of the spindle, dragging the rest of the chromatid behind them. The daughter chromosomes (split chromatids) continue their poleward movement until they form two compact clumps, one at each spindle pole. The last phase of cell division is called telophase. Here there is a pronounced condensation of the chromosomes, followed by the formation of a new nuclear envelope around each group of chromosomes. The chromosomes gradually uncoil to form the fine chromatin network like in interphase. After cell division occurs, another step might happen. It is called cytokinesis, which is the division if the cytoplasm into two cells. The old cell will pinch off in the middle along a cleavage furrow to form two new daughter cells.