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Mitosis
 

Biology Main Page
Chapter 6 main
Chromosomes
Mitosis
Meiosis
Vocabulary
Notes
Review
Mitosis is the process by which the cell ensures that the future generations of cells it produces are given the correct number and type of chromosomes.  Mitosis is actually part of a cycle the cells go through in its' lifetime.  The cell cycle consists of 3 parts; Interphase, m Phase (mitosis) and cytokinesis. 

The cell performs different functions at each stage of the cell cycle.  Each stage has sub-phases which are identified by what is happening in the cell at that time.  All eukaryotic cell goes through this cell cycle although the duration in each cell cycle is different for each cell.  An example of this would be the difference between the cells that line the stomach, and nerve cells.  The stomach is lined with epithelial cells that are replaced every other day.  Because of the acidic nature of the stomach these cells need to be replaced or the stomach would not last long because the epithelial cells protect it from the acids.  Nerve cells, once they are mature may never reproduce.  It is thought that some nerve cells can reproduce once every 30 years.  These are two drastic differences in the length of the cell cycle.  Other eukaryotic cells may reproduce but the length of the cell cycle varies from cell to cell.

Interphase is the time in which the cell prepares to divide.  It has 3 subphases;G1 S & G2.  In G1 the cell grows in size and increases the numbers of organelles during this time.  S phase stads for synthesis and  is the time in which the cell will duplicate the DNA material in the nucleus.  Up to this time, the DNA is in the state of chromatin, a long thin thread like state that is not duplicated.  In other words, there is a single copy up until S phase.  As S phase concludes, the DNA is still chromatin but, it is duplicated and each copy is connected to the original by a piece of protein called a centromere.  The centromere is equated to a snap like those found on a shirt.  They keep the copies called chromatid, together until separated in mitosis.  G2 follows S phase and is the last time the cell gets to grow in size and prepare for division.

Mitosis is the time when the cell will organize the DNA and pull the chromatid apart.  Mitosis has three subphases; prophase, metaphase, anaphase and telophase.

When the cell goes from interphase to mitosis there are some things that change in the cell.  Prophase is marked by the disappearance of the nuclear membrane.  The chromatin condenses into chromosomes by wrapping themselves around histones.  The centrioles in the cells begin to migrate to opposite ends of the cell and spindle fibers form and attach to each centriole. 

The cell then goes to metaphase which is seen as the time when the chromosomes line up in the middle of the cell and the centrioles are at opposite sides of the cell.  Spindle fibers have attached to the centromeres, which will be used to separate the chromatid. 

Anaphase is seen as the time when the chromatid are separated and they become single chromosomes.  This is followed by telophase, where the chromosomes are pulled to opposite ends of the cell , they decondense into chromatin and then the nuclear membrane begins to reappear.  The cell membrane will then begin to pinch in but will not pinch in two until C Phase.  C Phase stands for cytokinesis which is when the cell membrane will pinch in completely.  The result is two cells that have a diploid number of chromosomes.