Mr. T's Science Scene

Mitosis and Cancer

Now that you have the basics of mitosis (Interphase, Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis), we can move on to more specifics about that cell cycle and mitosis.

Mitosis is really a very small part of the cell cycle that includes "getting ready to reproduce" and "splitting".  During interphase, there are no less than three protein checkpoints to make sure the cell and the duplication of the chromosomes goes well.  At some point in the cell's growth a protein called Ras Cyclin will chemically check to see if the cell is big enough, mature enough to move forward with mitosis.  If it is, that means that there is enough cellular material to be split into two cells.  If it is not, the cell will need to grow some more.

If the cell is mature enough then a protein called p53 will check the chromosomes to see that they are undamaged and in good order.  If the chromosomes (DNA) is damaged, another protein will attempt to "fix it".  Usually the issue is a slight change in the A,T, C, G sequence.  If the DNA is severly damaged, the cell may not undergo mitosis and all- it will simply die.

If the DNA is fine then, towards the end of Interphase, the DNA/Chromosomes are copied.  At this point, ATM Nibrin, is sent in to make sure that the copies were done correctly and are exactly the same as the original DNA.  If not the copies will be "fixed".  If they cannot be fixed the process will stop.

The point at which Interphase transitions into Prophase is called the G2 portion of Interphase and is at the very end of that step.  Prophase sees the DNA already copied and the nucleus dissolving or dissolved.  In Metaphase the chromosomes line up and the centrioles begin to make their spindle fibers.  Anaphase is where the spindle fibers attach themselves to the centromeres (the middle of each chromosome) and start to pull them apart.  It is at this point that the last protein checkpoint, ATM MAD1, checks to make sure the spindle fibers have correctly attached themselves to the centromeres.  If so the separating happens, if not, the process stops.  The last part of mitosis is Telophase where the chromsomes are grouped together and two new nuclei form.  

If everything has gone well and all the checkpoints have been passed, the last part of the cell cycle occures in Cytokinesis where the cell will split in two (animals) or a new cell wall will form down the middle (plants) and the cells will begin growing and maturing.

Many cancers occur because there are mutations or problems with the proteins or the checkpoints.  Sometimes the protein does not form so the checkpoint will not happen.  Depending on which protein doesn't form or which checkpoint doesn't happen the consequences can be varied.  If the cell is immature and tries to reproduce the resulting cells will be malformed and unable to mature.  If the DNA or the DNA copies are wrong or damaged you will have developmental problems that can range from highlights in your otherwise dark hair or you can not grow a limb.  The amount of mutation to the DNA sequence is really the determining factor in physical issues or uncheck cellular growth.  If the spindle fibers do not correctly attach themselvs you may find that the organism is unable to reproduce new species or issues such as Downs Syndrome may happen.



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