A2-LEVEL AQA BIOLOGY NOTES
TOPIC 4: gene expression and cancer
Cancer = disease caused by uncontrolled cell growth and division
Benign Tumours
Development of tumours
Benign Tumours
- Slow growth
- Defined by a clear membrane or capsule
- Cells are usually functional and have normal shape and structure
- Retention of specialisation
- Spread directly by contact
- Rapid growth
- Not defined by a capsule; ill-defined area
- Cells do not retain specialisation
- Cells range in size and structure and are often not functional
- Necrosis in some parts due to inability of blood capillaries to deliver oxygen
- Can spread to anywhere in the body
- Causes damage to surrounding tissue
Development of tumours
- Cells possess ‘oncogenes’ which are capable of transforming the cell into a cancer cell
- They also possess ‘tumour suppressing genes’ which antagonise oncogenes
- Abnormal methylation of oncogenes and/or tumour suppressing genes cause the cell to begin dividing uncontrollably
- Override of cell cycle checkpoints
- Daughter cells are also cancerous
- Exponential growth
- Elevated oestrogen levels detected in some breast cancers