Topic F3

Question 1

What are the 3 types of genes that regulate cancer?

Answer 1

• Genes that promote cancer: oncogenes
• Genes that act to prevent cancer: tumour suppressor genes
• Genes that repair mutated DNA: mismatch repair genes

Question 2

What are the roles of functioning tumour suppressor genes?

Answer 2

• Prevent rapid cell cycling and thereby prevent rapid cell division and cell growth
• Control critical check points in the cell cycle
• Negatively control cell growth

Question 3

How do mutations in tumour suppressor genes cause cancer?

Answer 3

• Both functional copies of the tumour suppressor gene must be mutated for cancer to develop
• A loss of one copy of the functional gene can be inherited and predisposes the person to lose the second copy via somatic mutation as the cells are cycling through the cell cycle more quickly and with less control

Question 4

What is the retinoblastoma gene?

Answer 4

• A widely expressed tumour suppressor gene that acts as a regulator of cell cycle progression in every cell in the body and other cellular processes such as apoptosis
• this gene was first identified in individuals with hereditary retinoblastoma in which a mutation in one copy of the Rn gene is mutated giving the cells a growth advantage and if an additional somatic mutation occurs the cell will be strongly predisposed to develop cancer.

Question 5

What is tumour suppressor gene p53?

Answer 5

• When functional tumour suppressor gene p53 can induce cell death in cells with severe damage to their DNA
• prevents cell growth through cell-cycle arrest or induction of apoptosis via activating target genes
• if mutated in both copies allows the tumour to evade the apoptotic cell death pathway and therefore proliferate into tumours

Question 6

Is a tumour suppressor gene mutation sufficient to cause cancer?

Answer 6

• Generally no as it merely predisposes the cells to form cancers (different tumour suppressor genes have different penetrance)
• There is generally an accumulation of mutations including oncogenes in cancer cells.

Question 7

What are 2 examples of tumour suppressor genes?

Answer 7

• Rb (retinoblastoma gene)

- p53 gene

Question 8

What are mismatch repair genes?

Answer 8

• A group of 8 genes in humans (MSH, MLH, PMS) that repair DNA is errors occur during DNA replication
• MMR genes are often lost or defective in cancers
• Both copies of the MMR gene must be non-functional for the gene to lose its function
• A loss of function in certain MMR genes is implicated in colon cancers