1.4 - Epigenetics Flashcards
What is epigenetics?
the study of heritable changes in gene expression and gene function that cannot be explained by changes in DNA sequence
What is the epigenome?
all of the epigenetic marks on the genome
What can epigenetic arks be influenced by?
- diet
- chemical exposure
- medication
Explain DNA methylation
- prokaryotes and eukaryotes
- methyl group is transferred to the cytosine nucleotide
- carried out by writer enzymes and reversed by eraser enzymes
What is the role of a writer enzyme?
- transfer a methyl group to a cytosine
What is the role of an eraser enzyme?
- remove a methyl group from a cytosine
What is the effect of methylation in the promoter region?
- inhibits binding of TFs
What is the role of reader proteins?
- recognise methylated DNA
- they have an affinity for methylated cytosines
- they can then promote or inhibit the recruitment of other proteins (such as those involved in transcription)
How are epigenetic marks maintained in DNA replication?
- because DNA replication is semi conservative
- methylated cytosines will then only be on one strand
- reader proteins can then recruit writer proteins to methylate the other strand
What are epigenetic marks on histones?
- post-translational modifications
- impacts gene expression
- marks can be recognised by readers and removed by erasers
Name the 4 different histones found in nucleosomes
- H2A
- H2B
- H3
- H4
What can writers do to histones?
- acetylate
- methylate
- phosphorylate
- ubiquitinate
Explain H3K9ac
Histone 3, lysine (K) residue at position 9, acetylated
- DNA - , histones +
- acetylation by writers neutralises positive charge while recruiting readers
- looser packaged DNA
- more accessible to transcription machinery
Explain H3K27me3
Histone 3, lysine (K) residue at point 27, tri (3) - methylated
- readers affect relative nucleosome positioning and packaging
- in this case leads to highly packed nucleosomes (condensed)
- transcription machinery cannot get in
- genes silenced
What is the effect of which histone being methylated?
it can lead to either repression or activation of transcription
How are histone marks maintained during replication?
- nucleosomes disassembled before replication fork and reassembled afterwards
- parental histones partition equally between daughter strands, and new histones are added
- marks on parental histones recruit reader proteins to add marks to cytosolic histones
How many generations in plants and animals are required to prove transgenerational inheritance?
- animals - 3 (as it has to affect the germ line which is set aside early in development)
- plants - 2
What needs to happen for transgenerational epigenetic inheritance?
- marks must be present in the germ line
- need to be passed on even if there is no environmental trigger
- marks tend to be removed by eraser proteins in animal gametes - not removed in plants
- will be inherited if erasure is incomplete or marks are re-established
- happens in plants have not proven if in animals
How does epigenetics affect translation?
non-coding RNA
What are modulators of DNA methylation?
- phenolics
