8A- Epigenetic Control Of Gene Expression Flashcards
What can epigenetic control determine?
Whether a gene is expressed or not in eukaryotes.
It works through the attachment or removal of chemical groups to and from the DNA or histone proteins.
It doesn’t alter the base sequence of DNA.
It alters how enzymes and other proteins interact with and transcribe DNA.
Epigenetics can also occur as a response to changes in the environment.
How can epigenetic changes be inherited by offspring?
They inherit the DNA base sequence from their parents.
Most markers are removed but some are passed on.
This means some genes in the offspring can be affected by environmental changes that affected their parents or grandparents.
Eg. Epigenetic changes in some plants in response to drought have been shown to be passed on to later generations.
What does increased methylation do?
It switches a gene off.
It attaches to a CpG site, which is where a cytosine and guanine base are next to eachother.
Increase methylation changes the DNA structure so that transcriptional machinery can’t interact with the gene, so it’s not expressed.
What does decreased acetylation do?
Histones are proteins that DNA wraps around to form chromatin.
Chromatin can be highly condensed or less.
Histones can be epigenetically modifies by removing an acetyl group.
When the histones are acetylated they are less condensed so the transcription machinery can access more easily, allowing transcription.
When they’re removed the chromatin are highly condensed so nothing can be transcribed as the machinery can’t access them.
The enzyme HDAC is responsible for removing acetyl groups.
How to epigenetics lead to the development of disease?
Abnormal methylation of tumour suppressor genes and oncogenes can cause cancer.
Fragile X Syndrome causes learning and behavioural difficulties. It’s caused by a duplication mutation on the X chromosome called FMR1.
The repeat of the sequence leads to more
CpG and therefore more methylation.
The lack of the protein as the gene turns off leads to the symptoms.
How might drugs be able to treat diseases caused by epigenetic changes?
Epigenetic changes are reversible.
The drugs counteract the changes that cause disease. For example, stopping DNA methylation. Azacitidine is used in chemotherapy for the type of cancers that are caused by increased methylation.
HDAC drugs inhibit the activity of HDAC, so acetyl groups can’t be removed.
How do twin studies help determine the influences of phenotypes?
Studies of twins are useful in determining whether it is an environmental or genetic factor.
A difference in phenotype must be due to environmental factors.
