Tumours
Biology: AQA A Level, topic 8.2.11
Types of Tumour
Tumours are a cluster of cells that are growing uncontrollably. In some cases, tumours can cause cancer. There are two types of tumour:
Benign tumours
- Benign tumours are NOT cancerous.
- Benign tumours consist of cells that are dividing uncontrollably but the cells cannot spread and invade other tissues.
- Benign tumours can develop into malignant tumours.
Malignant tumours
- Malignant tumours are cancerous.
- Malignant tumours consist of cells that are dividing uncontrollably and spread into other tissues and around the body.
- Malignant tumours can be life-threatening and can grow rapidly.
Development of Tumours
Tumours can develop when gene expression is not regulated correctly. The development of tumours can happen in the following ways:
Tumour suppressor genes
- Tumour suppressor genes are genes found in all cells.
- These genes inhibit cell division to regulate the rate at which cells divide.
- Increased methylation of a tumour suppressor gene inhibits this gene.
- When tumour suppressor genes are not expressed, cell division is not inhibited. This causes the cells to divide uncontrollably.
Oncogenes
- Oncogenes are mutations in a gene called a proto-oncogene. Oncogenes are capable of transforming a cell into a cancerous cell because they cause excessive cell division.
- Proto-oncogenes normally stimulate cell division.
- Decreased methylation of a proto-oncogene causes proto-oncogenes to be over-expressed.
- Over-expression of proto-oncogenes stimulates cell division.
Oestrogen
- Oestrogen is a hormone that can bind to receptors on transcription factors in the cytoplasm.
- Oestrogen can increase the expression of genes.
- When genes are over-expressed, a tumour may develop.
- High levels of oestrogen have been detected in some breast cancers.
Test yourself on Tumours
Which of the following statements about tumours are true?
Which of these are NOT features of malignant tumours?
Which of these do NOT contribute to the development of tumours?
Which of the following statements about oncogenes are true?
What causes tumour suppressor genes to be inhibited?