Control of Gene Expression

Question 1

How are genes prevented from expressing themselves?

Answer 1

1. Preventing transcription and hence preventing the production of mRNA
2. Breaking down mRNA before its genetic code can be translated

Question 2

Arguments for embryonic stem cell research

Answer 2

1. Wrong to allow human suffering continue when there’s a possibility of alleviating it
2. Embryos are produced for other purposes e.g. fertility treatments, where they would destroy unused embryos which could be used for research
3. Wide range of medical applications due to totipotency

Question 3

Arguments against embryonic stem cell research

Answer 3

1. Undermines respect for human life and could progress to the use of foetuses for research
2. Move towards reproductive cloning and the information gained could be used to clone humans elsewhere
3. Human embryos are not the only source of stem cells

Question 4

How does oestrogen effect gene transcription?

Answer 4

1. Oestrogen = lipid soluble molecule => diffuses easily through the phospholipid portion of cell-surface mem.
2. Once inside cytoplasm, oestrogen combines with a site on receptor molecule of transc. factor.
3. The shape of the site and the shape of the oestrogen molecule complement one another
4. This causes a change in the shape of the receptor molecule
5. This change releases the inhibitor molecule form the DNA binding site on the transc. factor
6. The transc. factor can now enter the nucleus through a nuclear pore and combine with DNA
7. The combination stimulates transc. of a gene

Question 5

How does siRNA effect gene expression?

Answer 5

1. An enzyme cuts large double-stranded molecules of mRNA into smaller sections called siRNA
2. One of the two siRNA strands combines with an enzyme
3. The siRNA guides the enzyme to a mRNA by complimentary base pairing
4. Enzyme cuts the mRNA into smaller sections
5. mRNA no longer capable of being translated into a polypeptide
6. Gene is not expressed

Question 6

What are 2 potential uses of siRNA?

Answer 6

1. Identify the role of genes in a biological pathway. Some siRNA that blocks a particular gene could be added to cells. By observing the effects we could determine what the role of the blocked gene is.
2. Possible to use siRNA to block genes which cause disease.