Regulation of Transcription and Translation Flashcards
What is a transcription Factor ?
Where does it bind ?
protein that moves from the cytoplasm to DNA in the nucleus. It binds to a specific gene at the promoter region on the DNA, allowing RNA polymerase to bind and stimulate transcription, to form mRNA
What does it mean if a gene is switched off ?
the promotor region is blocked
transcription factor cannot bind to the DNA
transcription is prevented, therefore the gene is not expressed
Why can Oestrogen diffuse directly through the phospholipid bilayer ?
its small and lipid-soluble
Explain how Oestrogen initiates transcription
Oestrogen diffuses through the phospholipid bilayer into the cell as its lipid soluble
Once in the cytoplasm oestrogen binds to the receptor molecule of the transcription factor (Oestrogen and the receptor site are complimentary in shape to each other )
This causes a change in shape of the receptor on the transcriptional factor
When this happens it causes an inhibitor molecule to be released from the DNA binding site
The transcriptional factor then enters the nucleus
This then binds to the promoter region of the desired gene
Transcription begins through the stimulation and binding of RNA polymerase
Suggest how Oestrogen could cause breast cancer to develop
activates genes by releasing inhibitor
transcription can then occur
if the gene affected controls cell division then it would be activated
cause proto-oncogenes to be mutated to oncogenes
could lead to uncontrolled cell division
What is the definition of Epigenetics ?
Epigenetics is heritable changes in gene function without changes to the base sequence of DNA
What is the definition of the Epigenome ?
The layer of chemical tags that cover the DNA and histones.
This will determine the shape of the DNA and histone complex
What type of factors cause changes in gene function without mutating the DNA ?
Environmental factors such as alcohol, diet, stress, toxins, exercise, smoking
Describe how DNA is arranged
DNA has a double helix shape
DNA associates with/ wraps around histone proteins
Packaged and condensed into chromosomes
What is Epigenetic silencing ?
inactive genes are tightly packed and therefore do not get expressed
Explain how genes can be ‘switched on’
They have a weak association with histones
Therefore the DNA is less condensed.
Promoter region accessible to transcription factor
Transcription can occur.
mRNA is formed.
Explain how genes can be ‘switched off’
They have a strong association with histones
Therefore the DNA is more condensed
Promoter region is not accessible to transcription factor
Transcription cannot occur
mRNA is not formed
What effect does increased methylation have on gene expression ?
causes gene to not be expressed
How does increased methylation prevent gene expression ?
Causes DNA histone complex to become more condensed
promoter region is not accessible to transcription factors
Therefore Transcription cannot occur
mRNA is not formed
This results in the specific protein not being produced
What effect does decreased methylation have on gene expression ?
causes gene to be expressed
How does decreased methylation allow genes to be expressed ?
causes DNA histone complex to become less condensed
promoter region is accessible to transcription factors
Therefore transcription can occur
mRNA is formed
What happens during DNA methylation?
What is the enzyme involved ?
During DNA methylation, a methyl group is added to carbon atom 5 of a cytosine base
Catalysed by Methyltransferase
What are the two changes in the genes environment that inhibit transcription ?
decreased acetylation of histones
increased methylation of DNA
What is Acetylation ?
Acetylation is the process where an acetyl group is transferred to a molecule
What affect does decreased acetylation have on gene expression ?
causes genes to not be expressed
How does decreased acetylation prevent gene expression ?
Decreased acetylation increases the positive charges on histones and increases their attraction to phosphate groups resulting in more stronger attraction and therefore a more condensed DNA histone complex
This means promoter region is inaccessible to transcription factors
Transcription does not occur
mRNA is not formed
What effect does increased acetylation have on gene expression ?
causes genes to be expressed
how does increased acetylation cause genes to be expressed ?
causes DNA histone complex to become less condensed
Promoter region is accessible to transcription factors
transcription can occur
mRNA is formed.
Some colorectal cancer patients were found to have less DNA methylation than expected. Would this lead to more or less gene expression? How could this lead to cancer ?
More gene expression
More genes switched on
Less DNA methylation means DNA histone complex will be less condensed.
Promotor region is accessible to transcription factors
Transcription can occur
Oncogenes switched on
