Regulation of transcription and translation Flashcards
How do transcription factors control gene expression?
- transcription factors move from the cytoplasm into the nucleus
- each transcription factor has a site that binds to a specific base sequence of DNA in the nucleus
- When it binds, it causes the reigon of DNA to begin the process of transcription
- Mrna is produced and the information it carries is translated into a polypeptide
- when a gene is not expressed, the site on the transcriptional factor that binds to DNA is not active, therefore transcription is inhibited
What is the role of oestrogen in initiating transcription?
- oestrogen is a lipid soluble molecule that easily diffuses through the phospholipid bilayer of the cell surface membrane
-one inside the cytoplasm, oestrogen binds with a site on a receptor molecule of the transcription factor - The shape of oestrogen and the shape of site are complementary
- This causes the DNA binding site on the transcriptional factor to change shape, so it can now bind to DNA
- The transcriptional factor can now enter the nucleus and bind to specific base sequences on DNA
- This stimulates transcription
What is epigenetics?
The scientific field that provides an explanation as to how environmental influences such as stress and diet can alter the genetic influence of an organisms offspring
What is the epigenome?
- DNA and histones are covered in chemicals called tags
- These chemical tags form a second layer known as the epigenome
- The epigenome determines the shape of the DNA - histone complex
- The epigenome is flexible as to can respond to environmental changes such as stress and diet which can cause the wrapping or unwrapping of DNA
What are the effects of the epigenome on transcription?
They inhibit transcription by:
- increased methylation of the DNA
- decreased acetylation of associated histone
How does the DNA - histone complex relate to transcription?
- when the association of histones with DNA is weak, the DNA - histone complex is less condensed and is accessible to transcription factors which can initiate the production of MRNA, switching a gene on
- when the association of histones with DNA is stronger, the DNA - histone complex is more condensed and is not accessible to transcription factors which can initiate the production of MRNA, switching a gene off and inhibiting transcription
Describe the process and outcome of decreased acetylation?
Process = deacetylation is the process where an acetyl group is removed from a molecule. Acetyl groups are normally donated by acetylcoenzyme A.
Outcome = Deacetylation increases the positive charges on histones and therefore increases the attraction to the phosphate groups on DNA. The association between DNA and histones is therefore stronger and DNA is not accessible to transcriptional factors, inhibiting transcription
Describe the process and the outcome of increased methylation?
Process = Methylation is the addition of a methyl grouo, CH4 to a molecule. Methyl groups can be added to cytosine bases on DNA
Outcome = This inhibits transcription as it prevents transcriptional factors binding to DNA and causes the attachment of proteins that induce deacetylation, inhibiting transcription
Describe the link of epigenetics and diseases (specifically cancer)
- epigenetic changes are a part of development but can cause diseases
- altering epigenetic processes can lead to the abnormal activation or silencing of genes
- For example, scientists found that tissue from paitents with cancer had less methylation than normal
- less methylation would activate a gene and cause abnormal gene actvity
- epigenetic changes can also lead to an increase in frequency of mutations as epigenetics can lead to protective genes that repair DNA and prevent cancer being turned off
How can you treat diseases with epigenetic therapy?
- can help counteract changes in genes by causing them to be activated or deactivated
- therefore enzymes involved in methylation or acetylation can be inhibited
- also diagnostic tests can help detect the early stages of diseases like cancer, brain disorders and arthritis
How can the translation of MRNA be inhibited?
RNA interference (sIRNA)
What is the mechanism of sIRNA?
- An enzyme cuts large double stranded molecules of RNA into smaller sections of SIRNA
- One of the two sIRNA stands combines with an enzyme to MRNA by pairing with the complementary bases on a section of MRNA
- Once in position, the enzyme cuts the MRNA into smaller sections
- The MRNA is no longer capable of being translated into a polypeptide
- This means the gene is not expressed and is blocked
