The stages of mitosis.
There are five stages of mitosis: prophase, prometaphase, metaphase, anaphase, and telophase. The phases were identified according to the physical state of the chromosomes and the spindle. The final cell division after telophase, called cytokinesis, is considered by some to be the sixth phase of mitosis. Mitosis is the process involved in normal tissue growth.
Without the organized steps of mitosis, the chromosomes would be randomly distributed.
Mitosis is the eukaryotic division of a cell that produces two identical daughter cells from a single parent cell. Somatic cells of all multicellular organisms multiply by mitosis, and the process involves hundreds, perhaps thousands, of cellular proteins. The daughter cells are genetically identical to each other and to the parent cell and contain an equal distribution of chromosomes. Without the organized steps of mitosis, the chromosomes would be randomly distributed in the daughter cells and might not be viable.
Mitosis causes cells to regenerate and the skin to heal after a severe burn.
Prophase is the first stage of mitosis where the nuclear envelope begins to break down. The chromosomes, which are contained in the nucleus of the cell, begin to shorten, curve, and thicken. During this condensation process, a spindle, or network of hair-like filaments called microtubules, begins to extend outward from two centrosomes, or microtubule-organizing centers. Since there is only one centrosome in a cell that is not dividing, when mitosis begins, it replicates into two, each becoming the organizing center for one half of the spindle.
Prometaphase is a dynamic stage in which the nuclear envelope dissolves and proteins bind to centrosomes to become kinetochores. These then polarize at opposite ends of the cell. Metaphase is the third stage of mitosis. It is characterized by the chromosomes lining up along the middle of the cell at what is called a metaphase plate. In this way, as the cell continues to divide and the chromosomes separate, each new nucleus receives one copy of each chromosome.
Normally, only cells with correctly assembled spindles enter anaphase. At this stage of mitosis, the kinetochore microtubules shorten and the spindle draws the two sister chromatids of the chromosomes toward the poles of the cell. Each chromosome is pulled by its centromere. The poles then move apart when non-cenetochore microtubules cross each other. The last of the stages of mitosis is telophase, characterized by the arrival of the chromosomes at the spindle poles, where they begin to uncoil. Two new nuclear membranes are formed and two separate sets of unreplicated chromosomes are created.