A-Level Biology AQA Notes

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Tumours

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)	Tumours 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.

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