Let's Get Started
Let's review the process of cell division and apply our understanding of the cell cycle to a common illness that effects millions of people every year: cancer. Before you get started, don’t forget to print out your OnTRACK Biology Journal.
TEKS Standards and Student Expectations
B(5) The student knows how an organism grows and the importance of cell differentiation. The student is expected to:
B(5)(D) recognize that disruptions of the cell cycle lead to diseases such as cancer
Compare and contrast healthy cell division with cancerous cell growth.
Explain how cancer is caused by uncontrolled cell division.
Describe the safeguards cells have to prevent cancerous cell growth.
Relate mutations in DNA to cancer and describe possible causes of mutations.
How is healthy cell division different from cancerous cell growth?
Why is cancer caused by uncontrolled cell division?
What safeguards do cells have to prevent cancerous cell growth?
What are some possible causes of mutations in DNA that could lead to cancer?
What specific lifestyle choices can you make to reduce your risk of developing cancer?
- Cell Cycle
- Contact Inhibition
Introduction to Cancer Biology
Your body is constantly replacing old cells with new ones. In fact, your body makes millions of new cells every second! New cells are needed because at any given time some of your cells will reach the end of their life span and need to be replaced. You may also need new cells for growth or to repair damaged tissue. Cells go through a cell cycle to grow and divide in order to make new cells.
The amount of time it takes to complete the cell cycle varies in different cells. Some cells divide quickly—even within a few hours. Other cells may take days to complete the cycle. No matter how long it takes, the entire cell cycle is regulated and predictable. For a long time, scientists didn't know how the cell "knew" when to move through the stages of the cell cycle. For example, how does a cell know when to start replicating chromosomes? Through experimentation, scientists have discovered that the cell cycle is regulated by certain proteins called cyclins.
Most cells move through the cell cycle with no problem. However, there are times when cells do not follow the rules of normal cell division. Cancer is a disease that can occur when control of the cell cycle is lost.
Directions: Watch the videos Introduction to Cancer Biology, Control of Cell Division, and Mitosis for an introduction to cancer biology.
Controls of Cell Division/Cell Cycle Regulators
Let's review some of the safeguards cells have to ensure that damaged and/or abnormal cells don't complete the cell cycle and reproduce:
- During the G1 phase of mitosis (a part of interphase in which the cell prepares for mitosis), the cell checks to ensure that everything is ready for DNA synthesis. When DNA damage occurs or when the cell detects any defect, it will delay or halt the cell cycle in G1.
- A certain type of cyclin makes sure all chromosomes are attached to a spindle fiber before entering anaphase.
- Cells exhibit a characteristic called "contact inhibition." Cells will grow and divide until they begin to touch other cells. Then cells will slow down their division and will eventually stop reproducing.
- Cells have chemical signals that tell them when to divide more rapidly, and cells that are nearby send signals for other cells to slow down or stop dividing. These signals ensure that cells don't "overgrow" their boundaries and get in the way of other tissues. On the other hand, if you were to cut your finger, the cells around the wound would receive signals to divide more quickly so that the cut could heal.
- If a cell is damaged or has chromosomal problems, it receives a signal to "self-destruct"!
Directions: Watch Mitosis in Cancer to see what happens when cells to not respond to contact inhibition.
Uncontrolled Cell Growth: Cancer
Cancer is a disease of the cell cycle. Cancer cells do not respond to the signals and safeguards that are in place. Because cancer cells don't respond appropriately, they grow uncontrollably and can eventually damage the tissues around them.
If cancer cells continue to grow, they will eventually form a mass called a tumor.
Some tumors are benign and may be harmless. Malignant tumors are dangerous and can even cause death. Malignant tumors have the ability to leave their original growth site and move through the bloodstream to other areas of the body. This process is called metastasis. If this occurs, the tumor can invade new tissue and continue to grow uncontrollably in the surrounding tissue.
Directions: Watch Tumor Growth to learn more about how cancer can spread.
What Causes Cancer?
Most scientists agree that cancer is caused by mutations to the DNA within cells. But what causes mutations? Mutations can occur if DNA is not copied accurately when a cell divides. About 1 out of every 100,000,000 times, a mistake occurs when DNA is copied, which can lead to a mutation. However, there are a number of mechanisms in place to ensure that cells identify and correct damage to DNA.
Mutations can also be caused by external influences. Carcinogens are substances in our everyday environment that can cause mutations that lead to cancer. Take a look at some of the factors in our environment that can cause mutations.
A. Diet and Weight: The World Cancer Research Fund estimates that about 20% of all cancers diagnosed in the US are related to excess weight, physical inactivity, and/or poor nutrition and could be prevented. To learn more, visit Reduce Your Cancer Risk by the American Institute for Cancer Research.
B. Sun Exposure: Ultraviolet (UV) radiation in sunlight causes mutations in DNA that can lead to skin cancer. Artificial tanning beds are also dangerous, and studies have shown that indoor tanning beds increase the chances of developing melanoma, the most deadly form of skin cancer. To learn skin cancer prevention tips, visit the Skin Cancer Foundation.
C. Tobacco Use: Tobacco use can increase the risk of many types of cancer, including cancer of the lung, larynx (voice box), mouth, esophagus, throat, bladder, kidney, liver, stomach, pancreas, colon and rectum, and cervix, as well as acute myeloid leukemia. People who use smokeless tobacco (snuff or chewing tobacco) have increased risks of cancers of the mouth, esophagus, and pancreas. For more information on how tobacco use is related to cancer, visit the Centers for Disease Control and Prevention.
D. Viruses: Some viruses, like the human papillomavirus (HPV), can contribute to cancer formation. HPV is strongly linked to the formation of cervical cancer.