Cell division is the process of separation of two identical copies of the DNA content of a cell that has already duplicated its chromosomes. It is basically the fundamental event in cellular biology. There is no reproduction without cellular division. There is no growth. Even for an unicellular organism, if it does not divide Murphy law would warranty that something will eventually kill that organism. By making a copy of itself, the organism duplicates its chances of survival at least by being at two places at the same time. Cellular division it probably the most important physiological event in all biology and it is basically the strategy of life to overcome death. And, do not forget that uncontrolled cellular division means cancer.
In eukaryotes, the most common type of division is mitosis. Mitosis consists of four basic steps. When the cell is ready to divide, based on cellular signaling, the DNA, previously in loose chromatin, begins to aggregate into tightly wound chromosomes, and the nuclear membrane begins to disintegrate. This is called prophase. Next, the chromosomes line up at the middle of the cell, where they are attached to the centromeres at the sides of the cell by long microtubules called kinetochores. This is called metaphase. Once they are all connected in the middle of the cell, the kinetochores each take one sister chromatid of each chromosome and pull it in toward the edges of the cell, creating two distinct copies the cell's DNA on each side of the cell. This is called anaphase. Finally, the cell membrane must split, which is called cytokinesis. In animal cells, a clevage furrow cuts down the center of the cells and splits them into two. In plant cells, a cell plate forms between the two sets of DNA, which then hardens to become two sepearting cell walls. The chromosomes also turn back into chromatin and the two nuclear envelopes reform in a process called telophase.
Meiosis occurs in gamate formation in eukaryotes. Because gametes are haploid, but come from diploid cells, an extra level of cell division is required to make these cells haploid. In the first cell division, called Meiosis I, chromosomes form and pair up (independent assortment) and then cross over to increase genetic variation. Then the chromosomes are pulled to the sides as in mitosis, but the whole duplicated chromosome is taken, not just one chromatid. Telophase and cytokinesis now occur in the new haploid cells with replicated DNA. To create haploid cells without replicated chromosomes, another cell division then occurs, called Meiosis II, which is basically the same as mitosis. Meiosis thus creates four haploid cells from one diploid cell, and creates genetic variation in the meantime.
Cell division is important to create new cells from old cells, and in the case of mitosis, to create genetic diversity. Studying cell division is very important,
Cell division is necessary for following reasons:
1. Growth of Organisms
2. Maintenance of Chromosome Number
3. Maintenance of Nucleo-cytoplasmic Ratio ( NC ratio)
4. Repair 5. Reproduction in Unicellular organisms
6. Healing and regeneration
7. Genetic variations
8. Formation of gamete by meiosis.