Transcription of target genes is stimulated only when specific transcriptional factors move from the cytoplasm into the nucleus. The effect of oestrogen on gene transcription. Small interfering RNA (siRNA) aws a short, double-strand of RNA that interferes with the expression of a specific gene. Candidates should be able to - interpret data provided from investigations into gene expression - interpret information relating to the use of oncogense and tumor surpressor genes in the prevention, treatment and cure of cancer - evaluate the effect on diagnosis and treatement of disorders caused by hereditary mutations and those caused by acquired mutations.

Transcription factors are proteins that bind to a section of DNA to start the process of transcription there. There are specific transcription factors for specific genes.

 

Transcription factors are stimulated to attach to DNA by hormones. Hormones bind to transcription factors, changing their shape, and causes them to release an inhibitor which is blocking the binding site, they can then move into the nucleus (from the cytoplasm) and bind to DNA. Hormones also work by the second messenger model. 

Hormones that do this include oestrogen. It is lipid-soluble so can diffuse through the phospholipid bilayer into a cells cytoplasm where transcription factors are.

siRNA (small interfering RNA) can stop proteins being synthesised by breaking down mRNA so that only short, non-functional strands of amino acids are created. siRNA are complimentary to sections of mRNA and so will bind with it, when it does this an enzyme that it has attached to cuts the mRNA.

siRNA is created when an enzyme cuts a double strands of RNA into smaller pieces. The strands then split apart and one combines with an enzyme.

The creation of haemoglobin changes over time in humans because different genes are expressed at different ages: gamma-globulin as a child and beta-globulin as an adult (alpha-globulin is always produced). This changes the affinity of red blood cells to oxygen.

Tumour suppressor cells stop working after two mutations, this means that someone can be born with one mutation and so not have cancer, but be at greater risk of developing it as they are only one mutation away. This means that someone who does not have cancer may be treated with caution by doctors (in terms of giving x-rays which can cause acquired mutations) if they have a family history of cancer as that could mean one mutation is a hereditary mutation.

Tumour suppressor genes can be introduced to a tumour where the tumour suppressor genes are mutated so that the cell can manufacture functioning proteins to slow cell reproduction.

Oncogenes cause cancer by permanently activating protein receptors on cell surface membranes that stimulate cell reproduction. Destruction of these receptors will stop replication of cells and therefore prohibit the continued growth of a tumour.