A-LEVEL BIOLOGY AQA NOTES 
gene expression and cancer

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Tumours
  • Abnormal and fast cell division of mutant cells can form a tumour. 
Benign Tumours
Malignant Tumours
​Slow growth rate
​Faster growth rate
​Cells remain well-differentiated
​Cells tend to de-differentiate and become unspecialised
​Tumours are surrounded by a capsule made of dense tissue (compact structure)
T​umours are not surrounded by a capsule
​Cells produce adhesion molecules
​Cells stop producing adhesion molecule. Can spread through the body (metastasis)
​Can usually be removed by surgery.
 Chemotherapy and radiotherapy are used, which specifically target and kill rapidly dividing cells.

​Oncogenes & Tumour Suppressor Genes
  • Oncogenes are genes that stimulate cell division e.g. they may encode growth factors or cell cycle regulators.
  • Many cancers are found to have cells with abnormal DNA methylation (epigenetic changes). Detecting these changes can help diagnose, while reversing these changes may help cure these diseases.
  • Oncogenes can be hypomethylated in the promoter regions to upregulate transcription and expression to cause excessive proliferation in a tumour.
  • Tumour suppressor genes are genes that prevent tumour formation by repairing DNA damage, regulating cell division and promoting apoptosis.
  • Tumour suppressor genes can be hypermethylated in the promoter region to prevent transcription, allowing increased cell divisions with a higher mutation rate. resulting in cancerous tumours.
  • Oestrogen binds to a transcription factor, which activates genes to promote cell division. Increased oestrogen concentrations in the adipose tissue in the breast of post-menopausal women has been linked to breast cancer development.