Epigenetics and Gene Expression Flashcards
What is the definition of epigenetics?
The heritable change in gene function without changing the DNA base sequence
What can cause epigenetics changes?
caused by changes in the environment and they can inhibit transcription
What does epigenetics control?
Gene expression
What factors can cause epigenetic changes?
Diet, stress, toxins
What do the factors cause?
They cause epigenetic (chemical) tags to the DNA and this can control gene expression in eukaryotes
What is the epigenome?
a single layer of chemical tags on the DNA
What does the epigenome impact?
The shape of the DNA-histone complex and whether the DNA is tightly wound or not
If the DNA is tightly wound will it be expressed or not?
it will NOT be expressed
What is the tightly coiled DNA called?
Heterochromatin
If the DNA is unwound, will it be expressed?
YES, it WILL be expressed
HOW does decreased acetylation of DNA result in the inhibition of transcription?
Removing the acetyl groups from the associated histones makes the histones much more positive and thus are more attracted to the phosphate group on the DNA. This results in the DNA being much more strongly associated with the histones and this makes it hard for the transcription factors to bind.
The slightly les coiled DNA is called what?
Chromatin
Why is the DNA not expressed if it is tightly wound?
Becuase the transcription factors cannot bind so transcription is inhibited
What two ways do the changes in the environment inhibit transcription?
increased methylation of the DNA
decreased acetylation of associated histones
What is methylation of DNA?
Adding on a methyl group to DNA
What does increased methylation of DNA result in?
Inhibits transcription
What part of the DNA do methyl groups attach to?
The cytosine base
If a mutation occurs in the tumour suppressor gene what happens?
The tumour suppressor doesn’t produce the protein to carry out the function so cell division will continue
What two processes result in the formation of euchromatin/chromatin?
Decreased methylation
Increased acetylation
What two processes result in the formation of heterochromatin?
Increased methylation
Decreased acetylation
HOW does increased methylation of DNA result in the inhibition of transcription?
Because the methyl group is positively charged and the DNA is negatively charged, they are attracted to each other and tightly coil together. This prevents the transcription factors from binding to the DNA so the gene is not expressed
What does decreased acetylation of associated histones result in?
inhibition of transcription
What effect does adding acetyl groups have on the transcription factors being able to bind?
Because acetyl groups are negative, if more are added to the histone proteins, then it makes the histones much more negative so it repels DNA (as DNA is also negatively charged) so the DNA doesn’t tightly coil making it much more accessible for the transcriptional factors to bind and for transcription to occur.
What are two known mutated tumour suppressor genes that are linked to breast cancer?
BRCA1 & BRCA2
What are tumour suppressor genes?
The genes that code for a protein which slows down cell division or causes cell death (apoptosis) when a DNA copying error is detected
Describe hypermethylation of tumour suppressor genes?
an increased number of methyl groups are added to the gene causing it to tightly coil and results in the gene being inactivated and switched off so no transcription occurs and no proteins are made. Also, mitosis is not controlled so excess cell growth and division happens, therefore tumours develop.
Describe hypomethylation of oncogenes?
reduces the number of methyl groups attached which results in the gene being permanently switched on. So it continually produces the proteins which stimulates mitosis to happen even when it is not needed.
What do tumour suppressor genes ensure?
That you are only producing new cells when you need them for growth and repair so mitosis is being regulated
What are the two types of abnormal methylation?
Hypermethylation + Hypomethylation
What do oncogenes do?
They code for a protein which stimulates mitosis - cell growth/division
How can transcription of target genes be stimulated or inhibited?
When specific transcriptional factors move from the cytoplasm into the nucleus - they can either turn the gene on or off
What is control of transcription, controlling?
Controlling the formation of mRNA from DNA
What enables cells to become specialised?
Turning particular genes off or on
