gene expression and cancer

Question 1

1. What are the differences between benign and
   malignant tumours?

Answer 1

Cells of benign tumours cannot spread to other parts of the body (metastasise) whereas malignant tumours do; Cells of benign tumours grow slowly, cannot invade neighbouring tissues, whereas malignant tumours do.

Question 1

1. What type of tumours are cancer?

Answer 1

Malignant

Question 2

2. What are tumour suppressor genes?

Answer 2

Genes that can do one of the following: slow down cell division, repair mistakes in DNA, or initiate the death of cells (apoptosis). They maintain a normal rate of cell division, and ensure mutated cells die.

Question 3

3. What is the role of tumour suppressor genes
   in the development of tumours?

Answer 3

Cancer is caused when tumour suppressor genes are inactivated. This could be due to a mutation in the DNA that means the gene codes for a non-functional protein or it could be silencing of the gene due to epigenetics.

Question 4

4. What are proto-oncogenes?

Answer 4

Genes that stimulate a cell to divide when it is activated.

Question 5

5. What is the role of oncogenes in the development of tumours?

Answer 5

Cancer is caused when proto-oncogenes are permanently activated and become oncogenes. This could because the gene codes for a cell surface membrane receptor that is mutated and therefore permanently causes cell division in the absence of growth factor. Or the oncogene may code for a growth factor, which due to a mutation is produced in excessive amounts.

Question 6

6. What is the role of epigenetics of tumour
   suppressor genes in the development of tumours?

Answer 6

Hypermethylation (increased methylation) occurs in the promotor region of a tumour suppressor gene. This means transcription of the tumour suppressor gene is inhibited so the protein that controls cell growth is not produced. As TSG normally slow cell division, this leads to uncontrolled cell division by mitosis and the formation of a tumour.

Question 7

7. What is the role of epigenetics of oncogenes in
   the development of tumours?

Answer 7

If methylation is decreased in an in the promotor region of an oncogene, this means transcription factors can bind more readily, so more mRNA will be produced, and therefore more protein will be translated. This will lead to uncontrolled cell division and the formation of a tumour.

Question 8

8. How does decreased acetylation of a tumour
   suppressor gene increase the risk of tumours?

Answer 8

Less acetylation condenses the histone DNA complex. The TSG is inaccessible to transcription factors so is switched off (not expressed).

Question 9

9. What is the role of increased oestrogen
   concentrations in the development of some
   breast cancers?

Answer 9

Oestrogen are hormones that stimulate cell division in breast tissue. If there is an increase in the concentration of oestrogen in the blood, target cells will have receptors that bind with the oestrogen, and so activate the production of proteins important in cell division. This leads to uncontrolled cell division and the formation of a tumour