Biology - Cancer


Which hormones are involved in preventing cancer?

  • Proto-oncogenes and tumour suppressor genes
  • They are usually in balance
  • Proto-oncogenes stimulate cell division by 'switching on' cell cycle
  • Tumour suppressor genes suppress cell division by 'switching off' cell division
  • Too much proto-oncogenes leads to uncontrollable division and tumour growth. Usually these cells are destroyed, but just one being missed can cause cancer
  • During the cell cycle, there are 'checkpoints' to check for mutation - kills cell if gene unbalance
  • 50% of people with cancer have a mutated form of P53, a proto-oncogene
  • The rate of mitosis may also be effected by cell envrionment and growth factors 
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What is the difference between a benign and a mali

  • Benign = Encapsulated; won't spread. May still cause damage to adjacent tissues, for example, in the brain
  • Malignant = May spread from site of origin via the blood or lymphatic system. One cell coming off the tumour, landing somewhere else e.g. blood, invade other regions and form a secondary tumour in new area = metastasis
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What drugs are used to treat cancer and how to the

  • Vincristine and vinblastine: inhibit spindle assembly so the cell can no longer divide. This affects metaphase. However, these can affect healthy cells, like blood and hair cells, making patients susceptible to infection.
  • Taxol/Paclitaxal: Inhibits depolymerisation of spindle fibres which stop cell division. It promotes microtubule assembly and reduced the concentration of tubulin subunits necessay for polymerisation. Works in metaphase, arrests cell in this stage on bipolar spindles
  • Adriamycin and cytoxan: work in interphase by stopping DNA unwinding prior to replication
  • Methotrexate: works in interphase; stops cell making DNA nucleotides
  • Other drugs will affect G1, by preventing synthesis of enzymes -> cell can't enter S phase -> cell kills itself. Some may affect S phase due to radiation which may damage DNA. If severe damage is detected -> cell kills self 
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How do the 'checkpoints' work?

  • Stages of cell cycle is controlled by 'checkpoints'
  • At each one, transcription factors regulate transcription of genes to make a protein called cyclin
  • Cyclins control passage to next stage by activating specific enzymes which initiate reactions that occur in the next phase of cycle. 
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