Cell Division - Growth, Repair, Reproduction, and Cancer

Tumours

• Carcinogens (agents that can cause cancer)
  • Such as smoke, radiation
  • Cause mutations in the genes which control cell division (oncogenes)
  • Divide uncontrollably to produce a mass of cells - tumour
• Tumour cells do not respond to signals from nerves and hormones
  • Continue to grow
  • No programmed cell death occurs
• Types
  • Benign - does not spread from its origin (this is not cancer!)
  • Malignant - this is cancer
    • Spread throughout the body invading other tissues and destroying them
    • Cells can break off from the primary malignant tumour
    • They can travel/spread via the lymph system
    • Cause secondary tumours at other places (metastasis)
    • Hard to find and difficult to remove (all of) them
• Cancer may take many years to develop with few or no symptoms
  • Usually advanced when discovered
  • Cancer in the lungs
    • Can cause coughing up blood (haemoptysis)
    • Can block airways causing lung infections (pneumonia)
    • Removing all/part of the lung may be effective provided metastasis is not well advanced

Smoking and Cancer

• Smokers 18x more likely to develop lung cancer than non-smokers
• Causes one third of all deaths from cancer
• Increased risk
  • Starting at young age
  • Smoking high amount of cigarettes per day
  • High tar content of cigarettes
  • Long time of smoking
• Decreased risk
  • Stopped smoking
• Toxins also enter the blood and are excreted via the urine
  • Bladder cancer

Genes and Cancer

• Evidence
  • Tendency to develop cancer seems to be inherited
  • Tumour cells in some cancers have abnormal chromosomes
  • There is a positive correlation between mutations and carcinogens
• Oncogenes
  • Genes that turn cells into cancer (oncology = study of cancer)
  • Found when proto-oncogenes (normal versions of genes) mutate and become overactive
• RAS oncogenes
  • G-proteins are found on plasma membranes and enable cells to respond to growth factors
  • They are normally activated by enzymes found within the cell (GTPase)
  • Mutation of the RAS gene causes the production of GTPase deficient G-proteins
  • The mutated G-proteins remain active for longer causing tumours
• Myc oncogenes
  • Myc gene produces a protein needed for normal cell division
  • Common mutation switches the myc proto-oncogene from chromosome 8 to 14
  • There, it acts as an oncogene / abnormal cell division / tumour
  • When both ras and myc oncogenes present together, malignant cells result
• Tumour suppressor genes
  • Reduce normal activity by inhibiting cell division
  • Initiate cell death (apoptosis) if the cell’s DNA is damaged (due to mutations)
  • Mutation of this gene can cause a loss of its function
  • This will result in tumours