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  • Created by: polly
  • Created on: 02-02-13 15:44
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  • Cancer
    • What is it?
      • cells divide rapidly forming a mass of abnormally growing cells
        • tumour
          • may split, releasing clumps into the blood and lymph systems
            • can form secondary tumours when they lodge somewhere and continue rapid growth
              • malignant tumour
            • metastasis
        • invades surrounding cells
      • live longer than normal cells
    • Mutations that cause it
      • 15% of human cancers are due to viral infections
        • human papillomavirus is responsible for almost all cervical cancer cases
      • the mutations that cause cancer affect the control of the cell cycle
        • usually by disrupting chemical systems
      • multiple mutations result in a cancerous cell
        • hence why risk of cancer increases as age increases
        • this can often lead to:
          • inaccurate replication of DNA
          • decreased efficiency of DNA repair
          • increase in likelihood of chromosomesbreaking & rearranging
        • however, some cancers are the result of a single gene mutation
          • proto-oncogenes
            • code for proteins that stimulate cell cycle
              • 1 gene mutates = oncogene
                • oncogene produces uncontrolled amounts of the proteins
                  • so cell cycle is continuous = cancer
          • tumour suppressor genes
            • normally produce chemicals suppressing cell cycle
              • mutation = cycle cycle continuous = cancer
    • Role of environment
      • tar in cigarette smoke
      • chemicals in alcoholic drinks
      • asbestos
      • ionising radiation
      • UV  radiation in sunlight
        • malignant melanoma
          • cancer of cells that produce the pigment melanin
            • particularly damaging if sunburnt during childhood
          • melanin acts as a natural sunscreen
            • sunscreens either absorbs UV or reflect it


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