1Explain how the methylation of tumour suppressor genes can lead to cancer (3 marks)
Methylation prevents transcription of a gene
Protein not produced that prevents cell division
No control of mitosis
2Describe how altered DNA may lead to cancer (9 marks)
Mutation
Changes base sequence
Of oncogene
Of tumour suppressor gene
Changes protein structure
Tumour suppressor genes produce proteins that inhibit cell division
Mitosis
Uncontrolled cell division
Malignant tumour
3Explain what is meant by totipotent stem cell (1 mark)
Can differentiate into any cell type
4Explain how an activated oestrogen receptor affects the target cell (2 marks)
Receptor/transcription factor binds to promoter which stimulates RNA polymerase
Transcribes gene
5Explain what is meant my plutipotent stem cell (1 mark)
Can only give some cell types
6Explain how cells produced from stem cells can have the same genes yet be of different types (2 marks)
Different genes are activated
Promoters/transcription factors
7Give 2 characteristic features of stem cells (2 marks)
Cells that differentiate
Keep dividing
8Name the enzyme that makes a DNA copy of RNA (1 mark)
Reverse transcriptase
9Describe how alterations to tumour suppressor genes can lead to development of tumours (4 marks)
Methylation
Mutation
Tumour suppressor gene not transcribed / different aa sequence
Causes uncontrollable cell division