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Most eukaryotic cells go through a cell cycle, or a system of growth and division that is heavily regulated and controlled. The cycle includes stages called the growth stage, mitosis or the nuclear division stage, and cytokinesis or the actual division of the cytoplasm and the parts of the cell. This cell cycle is a very regular process that occurs each time a eukaryotic cell divides and also any time the resulting daughter cells divide. Any change from this prescribed set of stages results in the cell shutting down or dying in order to prevent the growth of mutant cells.
The cycle is divided into two phases: Interphase and Mitosis (M-phase). Cytokinesis is the last stage, so some say the cycle is three phases: Interphase, (Mitosis or Meiosis) and Cytokinesis.
Interphase - the cell gets energy and nutrients from its environment and duplicates its chromosomes. Three substages of Interphase are G1, S and G2. G1 (first gap) occurs before chromosome duplication. G1 is the phase where the cell gets nutrients and decides (checkpoint or restriction point) whether it is ready to divide. During S-phase, duplicates are made. G-2, cell prepares for Mitosis.
Mitosis - the now duplicated chromosomes are separated to form two nuclei. Mitosis is divided into:
1. Prophase (chromatin condenses and duplicated. Centrioles move to poles and chromosomes move to the center. The spindle fibers begin forming.
2. Metaphase (chromosomes line up on the metaphase plate and the mitotic spindles and centromeres of the chromosomes form.
3. Anaphase (spindle fibers pull apart the centromeres of eacah chromatids toward the opposite poles, resulting in twice as many chromosomes.
4. Telophase (nuclei in both sister cells begins to form and the two new cells, although still connected begin the cycle again (Interphase).
Cytokenisis finishes the division of the cell.
(Meiosis is the reproduction of sex cells, gametes. Meiosis results in four haploid daughter cells (Mitosis results in two diploid cells). Meiosis involves a cell division which is what Mitosis is, but then it divides again resulting in the four cells. Since meiosis is "one-way," it is not considered part of a cell "cycle." Meiosis is the process of sexual reproduction and unlike Mitosis, there is chromsomal crossover.)
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