8- Cancer =)

Question 1

Increased methylation of the promoter region of a tumour suppressor gene causes one type of human throat cancer.
In this type of throat cancer, cancer cells are able to pass on the increased methylation to daughter cells. The methylation is caused by an enzyme called DNMT.
Scientists have found that a chemical in green tea, called EGCG, is a competitive inhibitor of DNMT. EGCG enables daughter cells to produce messenger RNA (mRNA) from the tumour suppressor gene.
Suggest how EGCG allows the production of mRNA in daughter cells. (3)

Answer 1

1. binds to a.s. of DNMT
2. x methylate promoter region of tumour supressor gene
3. transcription factors ✔ bind
4. stimulates RNA polymerase

Question 2

Sometimes, a mutagenic agent causes DNA to break. A different enzyme called ATM binds to the broken DNA. This leads to the activation of a protein coded for by a tumour suppressor gene. The effect of ATM binding
is to stop cell division until DNA is repaired.
A mutation could result in a person having non-functional forms of the gene that produces ATM.
What can you predict about the possible effects of having a non-functional form of ATM? (3)

Answer 2

1. ATM x bind to broken DNA
2. DNA x repaired
3. cell division continues –> tumour forms
4. TS gene x activated
5. may have x effect on diploid organisms
6. which still has a functional ATM gene

Question 3

The KRAS gene codes for a protein called K-Ras. The protein relays signals from outside a cell to a cell’s nucleus, stimulating cell division.
An alteration in the KRAS gene produces an oncogene which can cause a tumour to develop.
Suggest and explain how an alteration in the KRAS gene can cause a tumour to develop. (3)

Answer 3

1. mutation un KRAS gene
2. Δ in signalling protein
3. uncontrollable cell division

Question 4

Explain how increased methylation could lead to cancer. (3)

Answer 4

• methyl group added to tumour suppressor gene
• inhibits transcription of TS gene
• uncontrollable cell division

Question 5

Give one way in which benign tumours differ from malignant tumours. (1)

Answer 5

x metastasis

x mention of rate of division ~

Question 6

Explain how the methylation of tumour suppressor genes can lead to cancer. (3)

Answer 6

• methylation prevents transcription of TS gene
• protein that prevents cell division/ causes apoptosis x produced
• x control of mitosis

Question 7

What is the link between sunbathing and skin cancer? (2)

Answer 7

1. Sun’s radiation contains UV light
2. UV light leads to mutation of genes which control cell division.