The Cell Cycle and Cancer The Cell Cycle

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The Cell Cycle and Cancer The Cell Cycle Powered By Docstoc
					The Cell Cycle and Cancer
Cancer is a disease of the cell cycle. Some
of the body’s cells divide uncontrollably and
tumors form.

                            Tumor in Colon
    Tumors in Liver
       Cancer Cells vs. Normal Cells
• Abnormal growth of cells is called a neoplasm
    Benign neoplasms are not cancerous
      - Encapsulated
      - Do not invade neighboring tissue or spread
    Malignant neoplasms are cancerous
      - Not encapsulated
      - Readily invade neighboring tissues
      - May also detach and lodge in distant places –
      - Results from mutation of genes regulating the cell
• Carcinogenesis – development of cancer
    Tends to be gradual
    May be years before cell is obviously cancerous
 There are several factors that regulate the
cell cycle and assure a cell divides correctly.

1.Before a cell divides,
  the DNA is checked
  to make sure it has
  replicated correctly. (If
  DNA does not copy
  itself correctly, a gene
  mutation occurs.
                               DNA replication animation:click
                               on DNA picture
DNA mutations disrupt the cell cycle.

                       Mutations may be
                       caused by:

                        1. radiation
                        2. smoking
                        3. Pollutants
                        4. chemicals
                        5. viruses
         Origins of Cancer: Oncogenes
• Mutations in DNA repair mechanisms
• Oncogenes
     Proto-oncogenes promote the cell cycle in
      various ways
     Tumor suppressor genes inhibit the cell cycle
      in various ways
     Both normally regulated in coordination with
      organism’s growth plan
     If either mutates, may lose control and
6     become oncogene
    Causes of

2. Chemical Signals tell a cell when to start
            and stop dividing.

                (Target cells animation: click on go
Due to DNA mutations, cancer cells ignore
the chemical signals that start and stop the
cell cycle.

      2 animations of cancer cells dividing: click on picture
Neighboring cells communicate with dividing
     cells to regulate their growth also.

          (Normal contact inhibition animation: click on petri dish)
While normal cells will stop dividing if there is a mutation in
the DNA, cancer cells will continue to divide with mutation.
Due to DNA mutations, cancer cells cannot
communicate with neighboring cells. Cells
   continue to grow and form tumors.

                Skin cancer

              (cancer cells dividing: click on
       Origins of Cancer: Telomerase
• Chromosomes normally have special material at
  each end called telomeres (end parts)
• These get shorter each cell division
• When they get very short
    The cell will no longer divide
    Almost like running out of division tickets
• Telomerase is an enzyme that adds telomeres
• Mutations in telomerase gene:
    Keeps adding new telomeres
    Allow cancer cells to continually divide
    Like counterfeit tickets
     Cancer Cells Versus Normal Cells

     Cancer Cells

    Normal Cell Division              Cancer Cells

1. DNA is replicated           1. Mutations occur in the
    properly.                      DNA when it is
2. Chemical signals start          replicated.
    and stop the cell cycle.   2. Chemical signals that
3. Cells communicate with          start and stop the cell
    each other so they             cycle are ignored.
    don’t become               3. Cells do not communicate
    overcrowded.                   with each other and
                                   tumors form.
            Treating Cancers

Cancer treatments include drugs that can stop
          cancer cells from dividing.
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