Section 6: Control System of Cell Cylce

A “control system” is made up of certain proteins within a cell and directs the timing and sequence of events of the cell cycle.  If something goes wrong in this system, cells lose control of the cell cycle.

Cancer is a disease caused by a disruption to the cell cycle leading to uncontrolled cell division.  It is usually caused by mutations or errors in genes. Cancerous cells form masses of tissues called tumors.  However, not all tumors are cancerous.  A benign tumor is an abnormal mass of essentially normal cells that always remain at the original site of growth.  It does not spread to other parts of the body and can usually be removed through surgery.  A malignant tumor is a mass of cancerous cells that destroys normal tissue as it grows.  If not killed or removed, this tumor can spread into surrounding tissue, or worse, break off and travel to other parts of the body.  The spreading of cancer cells is called metastasis.

There are many different causes of cancer.  Causes can be environmental, such as from cigarette smoke, air, or water pollution, or even from ultraviolet radiation from the sun.  Cancer can also be caused by genetic factors, such as viral infections that damage genes.  But no matter the type of cancer, all are disruptions in the cell cycle.  Treatment of cancer includes radiation therapy and chemotherapy.  Some skin cancers can be removed surgically.


  1. Explain why cancer occurs.
  2. Compare a benign and malignant tumor.
  3. Identify two causes of cancer.


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