Epigenetic control of gene expression Flashcards
What is epigenetics?
The study of changing gene expression without changing the genetic code
What does epigenetic control determine?
Whether a gene is switched on or off
What are epigenetic changes a response to?
changes to environmental factors
they also play a role in lots of normal cellular processes
What are epigenetic markers?
Chemical groups which are added or removed from the DNA or histones
What is the chromatin?
The combination of DNA and histones
What are histones?
Proteins which combine with DNA
What is the epigenome?
The chemical layer that surrounds the chromatin
What are examples of epigenetic markers?
Methyl groups
Acetyl groups
Are epigenetic changes inheritable?
Most epigenetic marks are removed during fertilisation
Some are passed onto offspring
The offspring can be affected by the environmental changes which their parents or grandparents experienced
What are the two ways of controlling gene expression?
Methylation
Acetylation
Where does the methyl group attach?
CpG sites which is where guanine and cytosine are next to each other
What does increased methylation cause?
It causes the gene to become more condensed
The transcription factors cant access the DNA so it cant be transcribed
Increased methylation…
…inhibits transcription
Decreased methylation…
…allows transcription to take place
Where do acetyl groups attach to?
Histones
What does decreased acetylation cause?
It causes the chromatin to become more condensed so the transcription factors aren’t able to access the DNA and transcription cant take place
Increased acetylation…
…allows transcription to take place
Decreased acetylation…
….inhibits transcription
What enzyme is responsible for removing the acetyl groups?
Histone deacetylase
What role does epigenetics play in fragile X syndrome?
There are more CpG sites in the gene than usual as the base sequence CGG is repeated which mean that there is increased methylation.
This causes the gene to be switched off so the protein it codes for isn’t produced
What role does epigenetics play in Angelman syndrome?
The paternal allele is switched off by methylation so the gene is not transcribed
What role does epigenetics play in Prader Willi syndrome?
It is caused by loss of function of chromosome 15
The paternal gene is silenced by methylation so the protein isnt produced
Are epigenetic changes reversible or irreversible?
Reversible
