Mutations, Gene Expression and Cancer

Question 1

Explain what is meant by the terms totipotent and pluripotent. (2)

Answer 1

1. Totipotent cells can give rise to all cell types
2. Pluripotent can only give some cell types

Question 2

Explain how cells produced from stem cells can have the same genes yet be of different types. (2)

Answer 2

1. Different genes are switched on / off
2. Correct and appropriate reference to factors /mechanisms for gene switching
3. E.g. reference to promoters / transcription factors

Question 3

Describe the mechanism by which a signal protein causes the synthesis of mRNA (6)

Answer 3

1. Signal protein binds to
2. Receptor on surface membrane
3. Messenger molecule moves from cytoplasm and enters nucleus
4. Produces transcription factor
5. Binds to promoter region
6. RNA polymerase transcribes target gene

Question 4

Explain how oestrogen enables RNA polymerase to transcribe its target gene. (6)

Answer 4

1. Oestrogen diffuses through cell membrane
2. Attaches to ERα receptor
3. ERα receptor changes shape
4. ERα receptor leaves protein complex which inhibited it’s action
5. Oestrogen receptor binds to promoter region
6. Enables RNA polymerase to transcribe target gene

Question 5

Compare the structure of dsRNA and DNA. (4)

Answer 5

SIMILARITIES - 2 MAX
1. Polynucleotides of nucleotides
2. Contain Adenine, Guanine, Cytosine
3. Have pentose sugar
4. Double stranded
DIFFERENCES 2 MAX
1. dsRNA contains uracil, DNA contains thymine
2. dsRNA contains ribose DNA contains Deoxyribose
3. dsRNA is Shorter than DNA; fewer base pairs in length

Question 6

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

Answer 6

1. Methylation prevents transcription of gene
2. Protein not produced that prevents cell division
3. No control of mitosis

Question 7

Describe how alterations to tumour suppressor genes can lead to the development of tumours. (4)

Answer 7

1. Increased methylation (of tumour suppressor genes)
2. Mutation
3. Tumour suppressor genes are not transcribed
4. Results in uncontrollable cell division;

Question 8

Describe what is meant by a malignant tumour. (4)

Answer 8

1. Mass of undifferentiated / totipotent cells
2. Uncontrolled cell division
3. Metastasis form new tumours
4. Spread to other parts of body

Question 9

Describe how altered DNA may lead to cancer. (6)

Answer 9

1. Mutation
2. Changes base sequence
3. Of gene controlling cell growth
4. Of tumour suppressor gene
5. Change protein structure / non-functional protein
6. (tumour suppressor genes) produce proteins that inhibit cell division
7. Mitosis
8. Uncontrolled cell division
9. Malignant tumour

Question 10

Define epigenetics (1)

Answer 10

1. Heritable phenotype changes that do not involve alterations in the DNA sequence

Question 11

Describe the difference between malignant and benign tumours (1)

Answer 11

1. Malignant tumours metastasise (spread) WHEREAS benign tumours do not metastasise

Question 12

What do tumour suppressor genes do? (1)

Answer 12

1. Slows cell division