Topic 8: regulation of transcription and translation Flashcards
Transcription of a gene will only occur when a transcription factor moves from the cytoplasm into which part of the cell?
Nucleus
What is a transcription factor?
Proteins that can bind to different base sequences on DNA, and therefore initiate transcription of genes.
Define epigenetics.
Epigenetics is the heritable change in gene function, without changing the DNA base sequence.
What factors can cause epigenetic changes?
Diet Stress Toxins
describe the role of the steroid hormone, oestrogen, in initiating transcription.
Oestrogen is lipid soluble and dissolves through the plasma membrane into the cytoplasm.
It binds to the complementary shaped receptor on the transcription factor forming a hormone-receptor complex.
This causes the DNA binding site on the transcription factor to change shape and the inhibitor is released.
The transcription factor moves into the nucleus and now the DNA binding site has changed shape, it is complementary in shape to bind to the DNA.
TF binds to the promoter region of the DNA and attracts co-factors to bind to it.
This initiates transcription
Describe and explain the impact of DNA methylation.
Increased methylation of DNA inhibits transcription. When methyl groups are added to DNA, they attach to the cytosine base.
This prevents transcriptional factors from binding and attracts proteins that condense the DNA-histone complex.
In this way, methylation prevents a section of DNA from being transcribed.
Describe and explain the impact of histone acetylation.
Decreased acetylation of associated histones proteins on DNA inhibits transcription.
If acetyl groups are removed from the DNA then the histones become more positive and are attracted more to the phosphate group on DNA.
This makes the DNA and histones more strongly associated and harder for the transcription factors to bind.
Describe how abnormal methylation could result in cancer.
Tumour suppressor genes could become hypermethylated, meaning an increased number of methyl groups attached to it.
This abnormal methylation results in the gene being deactivated and becomes turned off.
The opposite could occur in oncogenes, as they may be hypomethylated, reducing the number of methyl groups attached. This results in the gene being permanently switched on.
Describe the role of the tumour suppressor gene & oncogene in tumour development.
1) Tumour suppressor gene
These genes produce proteins to slow down cell division and cause cell death if DNA copying errors are detected.
2) Oncogene
A mutated version of a proto-oncogene, which creates a protein involved in the initiation of DNA replication and mitosis cell division when the body needs new cells. Oncogene mutations can result in this process being permanently activated to make cells divide continually.
describe how RNAi can inhibit translation
An enzyme can cut the mRNA into siRNA.
One strand of the siRNA then combines with another enzyme.
This siRNA- enzyme complex will bind via complementary base pairing to another mRNA molecule.
Once bound, the enzyme will cut up the mRNA so it cannot be translated.
