Lecture 15: Epigenetics Flashcards
What are the two forms of info in the genome of cells?
Genetic info and epigenetic info
What is epigenetic info?
additional info that can be modified for the regulation of gene expression.
Define epigenetics?
On or over the genetic info encoded in the DNA. Is the study of reversible heritable changes in gene function that occur without a change in the sequence of nuclear DNA.
What eventually happens to epigenetic markers?
They are lost or modified more easily.
What is tight packing?
8 different proteins form a histone octamer with DNA wrapped around it to form a nucleosome. DNA is tightly packed around nucleosomes which are made of histones. the nucleosomes form more complex structures called chromatin fibres.
What does how tightly DNA is wrapped around mean?
Determines how well RNA polymerase can be recruited and change gene expression patterns.
What can alter higher order nucleosome structure?
Post-translational modification of histone tails be methylation, acetylation or phosphorylation
What else can nucleosome structure be regulated by?
ATP-dependent chromatic remodellers.
What are the epigenetic markers?
DNA methylation and histone modification
What do methyltransferase do?
Transfer methyl groups to cytosines of CpG dinucleotides on both strands.
What represses expression?
Methylated CpG islands close to promoter regions of genes
What happens to methyl groups during DNA replication?
They are transferred to the new strands
How many histones can be modified by how many processes and what processes?
4, 3, Ac, Me, P.
What does histone acetylation do?
Loosens chromatin packaging and correlates with transcriptional activation
What adds and removes the acetyl groups?
acetyl-co-A and histone deacetylases
What is the effect of removing the acetyl groups?
re-establishes the positive charge in the histones which are associated with repression of transcription.
What carries out histones methylation?
histone methyl transferase
Where is histone methylation usually concentrated and what is it associated with
N terminus and silencing of gene expression.
What is gene activation and silencing correlated with?
H3 and K9 acetylation and H3 and K9 methylation.
What can different modifications at the same site do?
Have different effects on gene expression
What else can histone methylation do?
can increase or decrease gene expression of nearby genes.
What is histone phosphorylation associated with?
increased expression of proliferation associated genes but also with gene expression silencing.
What increases during cell stress and DNA damage?
Histone phosphorylation
What is associated with aggressiveness of cancer?
phosphorylation of histones near oncogenes
Explain which of the modifications are retained or lost during cell division
Histone acetylation patterns are replication, histone methylated ones are lost
What proteins promote and repress expression?
TrxG and PcG
Explain why epigenetic change is important
Development of multicellular organisms is possible because epigenetic markers help maintain different cell states. Epigenetics mediates the silencing of alleles during imprinting. Some changes are passed on that allow us to adapt to environmental change. Changes in epigenetic control can lead to cancer.
explain how epigenetic changes are important for maintaining cell differentiation
pluripotency genes eg OCT4 are methylated at H3K4 and expressed. late differentiation genes are marked by H3K27 in a manner dependent on the particular committed cell type.
