4. Gene expression and cancer

• Cancer


  A mutation in the genes which regulate mitosis
• Malfunction in the genes which regulate mitosis can lead to cancer

  1. Mitosis not regulated - genes which regulate can no indicate when it should start and stop

  2. Leads to uncontrolled cell division/ mitosis

  3. Can result in the formation of a tumour
• Main characteristics of benign and malignant tumours

  • Benign tumours
  • Malignant tumours
• Benign tumours


  • Non-cancerous
  • Can grow very large but only at a slow rate
  • Produce adhesive molecules to stick to a particular tissue
  • Surrounded by a capsule - remain compact and unable to travel to other parts of the body
• Why are benign tumours non-cancerous?

  • Produce adhesive molecules which all them to stick together and stick only to a particular tissue
  • Also surrounded by a capsule - remain compact and unable to travel to other parts of the body
• Treatment of benign tumours

  1. Removed by surgery

  2. Rarely return - as all the tumour cells are removed within capsule
• Impact of benign tumours


  • Localised only to one part of the body
  • Often not life threatening - depending on location of tumour may still cause pressure and blockages for certain organs
• Malignant tumours


  • Cancerous
  • Can grow large at a rapid rate
  • Cells can become unspecialised again
  • Do not produce adhesive
  • They metastasis - they tumours can creak off and spread to other parts of the body
  • Forming secondary tumours in other parts of the body
  • Tumours is not encapsulated
  • Able to grow projections into surrounding tissues
  • Eventually developing it's own blood supply
• Treatments and impact of malignant tumours

  1. Life-threatening

  2. Harder to remove every tumour cell to prevent regrowth

  3. Hard to locate all tumour cells

  4. May occur in area of the body where surgery is not an option

  5. Treatment may involve radiotherapy (radiation) and chemotherapy (drugs and chemicals to slow down cell division)
• Tumour suppressor genes


  • Slowing down mitosis/ cell divison
  • Causing cell death if DNA copying errors are detected - cause them to self-distruct
• Oncogenes


  • Create proteins involved in initation of DNA replication in Interphase
  • When new cells are needed
• How a mutation in proto-oncogene causes uncontrolled cell division

  1. Mutation will mean oncogene is permantly activated

  2. Causing constant uncontrolled cell division

  3. Even if body doesn't reqire new cells
• How a mutation in tumour suppressor genes leads to tumour cells

  1. Protein not produces

  2. Cell division continues at an uncontrollable rate

  3. Mutated cells with DNA copying errors wouldn't be identified and destroyed
• Examples of mutated tumour suppressor genes

  • BRAC1 and BRAC2
  • Liked to breast cancer
• Hypermethylation of tumour suppressor genes

  • An increased attachment of methyl groups to tumour suppressor genes
  • Cause heterochromatin - transcriptional factors unable to bind to gene
  • Genes become turned off and inactive
  • Lack of control of mitosis and excess cell growth which can lead to the formation of cancerous tumours
• Hypomethylation of oncogenes


  • Reducing number the number of methyl groups attaches to oncogenes
  • Causes chromatin - transcriptional factors able to bind easily to genes
  • Gene is permanently switched on
  • Mitosis will continue to occur even when not needed - leads to uncontrolled cell division and the development of cancerous tumours
• Where is oestrogen produced before menopause?

  in the ovaries
• Where is oestrogen produced after menopause?


  • Made in fat cells within breast tissue
  • Increasing risk of breast cancer in women post-menopause
• How does oestrogen lead to uncontrolled cell division?

  1. Oestrogen binds to genes which initiates transcription

  2. If this is a proto-oncogene - becomes permanently tuned on and activates cell division

  3. Results in the production of oestrogne
• How does oestrogen continue tumour growth?

  1. Tumours can result in more in more oestrogen production

  2. Interferes with genes involved in transcription

  3. Increasing the size of the tumour