The Cell Cycle and Cancer
Cancer is a disease of the cell cycle. Some
of the body’s cells divide uncontrollably and
Tumor in Colon
Tumors in Liver
Cancer Cells vs. Normal Cells
• Abnormal growth of cells is called a neoplasm
Benign neoplasms are not cancerous
- 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
DNA replication animation:click
on DNA picture
DNA mutations disrupt the cell cycle.
Mutations may be
Origins of Cancer: Oncogenes
• Mutations in DNA repair mechanisms
Proto-oncogenes promote the cell cycle in
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
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
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.
(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
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
Cancer treatments include drugs that can stop
cancer cells from dividing.
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