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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