3.8. The Cell Cycle

• The three stages of the cell cycle are interphase, mitosis, and cytokinesis.
• Typically a mammalian cell takes about 24 hours to complete a cell cycle, of which 90% is spent in interphase
• Cancer is a group of diseases (around 200 in total) caused by uncontrolled cell division. It is the result of a genetic mutation. This leads to uncontrollable growth of cell divisions
• As a consequence, a group of abnormal cells can form a tumour, that develops and constantly expands in size. Tumours can develop in any organ of the body
• Tumours are most commonly found in the lungs, prostate gland, breasts and ovaries, large intestines, stomach, oesophagus and pancreas.
• Tumours only become cancerous if its state changes from benign to malignant. Which can lead to life threatening consequences
• Benign tumours do not spread beyond their original site and remain localised. They grow slowly and don't invade surrounding tissues or organs. Benign tumours usually have a low risk of becoming cancerous
• Malignant tumours are more dangerous as they can spread throughout the body via blood vessels and lymphatic system. Malignant tumours often cause damage to healthy tissue and organs. These types of tumours are also known as carcinomas
• The rate of mitosis can be affected by the environment of the cell and by growth factors. It is also controlled by two types of gene. A mutation of one of these genes results in uncontrolled mitosis.
• The mutant cells formed are usually structurally and funtionally different from normal cells. Most mutated cells die, however, any that survive are capable of forming clones of themselves and forming tumours.
• Malignant tumours grow rapidly, are less compact. Whereas benign tumours grow slowly, are more compact and are less likely to be life threatening
• The treatment of cancer often involves killing dividing cells by blocking a specific part of the cell cycle. This way the cell cycle is disrupted and cell division, and hence cancer growth, ceases.
• Drugs used to treat cancer usually disrupt the cell cycle by:

  • Preventing DNA from replicating
  • Inhibiting the metaphase stage of mitosis by interfering with spindle formation
• The problem with the drugs to cure cancer is that they disrupt normal cell cycles. As cancer has a fast rate of division they are damaged to a much greater degree by these drugs.
• Normal body cells such as hair producing cells that happen to divide rapidly are vulnerable to the drug's damage. This explains frequent hair loss observed in patients undergoing the treatment