The Cell Cycle

• Only some cells in mulit-cellular organisms retain the ability to divide.
• Stages of the cell cycle:

  • interphase
  • nuclear division
  • division of the cytoplasm - cytokinesis
• The interphase, which occupys most of the cell cycle , and is sometimes known as the resting phase as no cell division takes place.
• Nuclear division is when the nucleus divides into either two (mitosis) or four (meosis).
• Cytokinesis, which follows nuclear division, and is the process by which the cytoplasm divides to produce either two or four new cells.
• The length of the compelete cell cycle varies depending on the type of cell.
• Typically a mammalian cell takes about 24 hours to complete a cell cycle (90% is interphase)
• Cancer is a group of diseases caused by a growth disorder of cells.
• Cancer is the result of damage to the genes that regulate mitosis and the cell cycle, which leads to uncontrolled growth and division of cells.
• A tumour is a group of abnormal cells that developes constantly and expands in size.
• Tumours can develop in any organ of the body, but are most commonly found in the lungs, prostate gland, breast and ovaies, large intestine, oesophagus and pancreas.
• A tumour becomes cancerous if it changes from benign to malignant.
• The treatment of cancer often involves killing dividing cells by blocking a part of the cell cycle.
• Drugs used to treat cancer (chemotheraphy) usually disrupt the cell cycle by:

  • preventing DNA from replicating
  • inhibiting the metaphase stage of mitosis by interfering with spindle formation
• The problem with chemotheraphy is that they also distrupt the cell cycle of normal cells.
• As cancer cells have a particularly fast rate of division, they are damaged to a greater degree than normal cells.
• People suffer hair loss from chemotheraphy because normal body cells, such as hair-producing cells, that divide rapidly are also vulnrable to damage.
• The cell cycle

  A) growth

  B) DNA synthesis

  C) preparation for mitosis

  D) mitosis