epigeneitcs Flashcards
What are epigenetic changes
Chemical modifications to chromosomes
What happens in epigenetic changes
Chemical tags are added onto DNA or associated proteins called histones
When does epigenetic changes occur
During development of an organism and by environmental factors
Define epigenetics
Changes in DNA that alter the expression of genes without changing the base sequence of DNA itself. These changes can be caused by environmental factors and are heritable
What is the epigenome of a cell
The chemical tags attached to the DNA and histones. Lifetime accumulation of signals that the cel has received from the environment
How are epigenetic changes able to regulate transcription
By remodelling chromatin (complex formed from DNA and histones)
What do signals from the environment do to the chromatin
Cause chemical tags to be added to histones or the DNA, changing how tightly packed the chromatin is
What occurs when chromatin is too tightly packed
The DNA wrapped around it may not be accessible to RNA polymerase and transcription factors. This means RNA polymerase cannot bind to the DNA and transcription cant occur and the gene will not be expressed
What is tightly packed chromatin called
heterochromatin
What happens when chromatin is loosely packed
The DNA is exposed and is accessible to RNA polymerase and transcription factors and the gene will be transcribed
What is loosely packed chromatin called
euchromatin
How do chemical tags control which genes are switched on or off
By regulating the formation of euchromatin or heterochromatin
What is one method used to regulate gene expression
Methylation of DNA
What occurs in methylation
Methyl groups are added to DNA at specific locations called CpG sites
What is a CpG site
Where cytosine is found next to guanine in the DNA chain
How are methyl groups added to the cytosine bas
By an enzyme called DNA methyltransferase
What does DNA methylation always do to transcription
Inhibits it
What is the first way DNA methylation prevents transcription
Transcription factors may no longer be able to bind to the DNA, there for RNA polymerase cant bind
What is the second way DNA methylation prevents transcription
The methyl groups may attract proteins that condense the chromatin, making the genes inaccessible for transcription
What process removes Methyl groups
Demethylation
What does demethylation do
The chromatin becomes more loosely packed and the genes are more accessible for transcription
What is another method used to regulate gene expression
Histone modification (adding chemical tags to histone proteins)
What is accetylation
The process of adding an acetyl group to histone proteins
What are acetyle groups added to
lysine amino acids found in the histone protein
How are acetyle groups added to lysine amino acids
By acetyl-coenzyme A
What does accetylation do
Neutralises the positive charge of the lysine, reducing the attraction between the DNA and the histones
What does accetylation do to the chromatin
Makes it more loosely packaged, forming euchromatin where genes are accessible for transcription
What happens in deacetylation
Reverse reaction where an acetyl group is removed from the lysine in the histone proteins
What does deacetylation do to chromatin
Makes it more compact which forms heterochromatin, which prevents genes from being transcribed
What is the other way histones can be modified
Methylation
What happens in methylation
Methyl group is added to the amino acid lysine
What does methylation do to chromatin
Condenses it to form heterochromatin which silences genes
What does histone methylation play an important role in
Silencing one of the X chromosomes in female mammals
How are epigenetic changes made to chromosomes
Adding chemical tags to histones
