Section 6: Control System of Cell Cycle

A “control system” made up of specific proteins within a cell directs the cell cycle’s timing and sequence of events.  Cells lose control of the cell cycle if something goes wrong in this system. The cell cycle is vital because any disruptions can lead to cancer.  This disruption leads to uncontrolled cell division.

Normal cells follow a typical cycle.  They grow, then divide, and then die.  However, cancer cells grow, divide, multiply, and reproduce other abnormal cells.  When cancer cells multiply, they often form a tumor that can spread to other body parts. Cancer is a disease caused by a disruption to the cell cycle leading to uncontrolled cell division.  Mutations or errors in genes usually cause it. 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 body parts 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 of cancer can be environmental, such as cigarette smoke, air or water pollution, or even 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.  In addition, 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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