Lecture 5 Flashcards
What is a classic epigenetic mark?
DNA-methylation : 5-methylcytosine
What is special about 5-methylcytosine
Can be propagated across divisions
associated with gene transcription
What are CpG islands?
CG dinucleotides enriched at many promoters
How is the nucleosome organized?
four histones with 2 copies each (octamere)
What are the core histones?
H2A, H2B, H3, H4: H1 is a linker histone (one per nucleosome)
Where does histone - DNA contact take place?
Histone fold domain
hat is special about the histone fold domain?
Unstructered N-terminal (site of post translational modification)
What do H2A, H2b histones form and what does H3 and H4 histones form?
(H2A, H2B) dimers and (H3, H4) tetrameres respectively
What does chormatine folding do?
GHene silencing
What is the difference between constitutive heterochromatine and facultative heterochromatine
constitutive heterochromatine:
independent of cell type
little transcription
repetetive sequences (structure regions)
facultative heterochromatine:
inactive gene regions
cell type specific
coding regions
What are functions of nucleosomes
packaging
signaling
transcription obstacle
What are the two classes of epigenetic regulators
chromatine remodelers
chromatine modifiers
What is the role of chromatine modifications
development (gene expression patterns) and transcription
signature modifications are essential for genetic processes
where are histones normally modified?
N-terminally (histone code are all modifications)
What does lysine acetylationd do?
lysine has positive charge, which is removed by acetylation -> eviction of nucleosome and enables transcription
Are epigenetic marks reversible?
Yes
What are READER domains and how do they work?
Site of Post translational modification allow for recruitment and regulation
When are histones normally synthesized?
During the S-phase
What are histone chaperones and what do they do?
Prevent histone-DNA aggregation -> bind histones and are specific for histone variants
What does the variant H2A.Z do?
Marks boundaries of nucleosome-free and nucleosome-containing regions
Do histone chaperones use ATP?
No
Do histone remodelers use ATP?
Yes
What do histone remodelers do?
Can establish spacing between nucleosomes, can grant DNA access, can edit Nucleosomes
What happens during transcription elongation?
Nucleosomes dissasembled and reassembled: Histone chaperone FACT removes H2A/H2B for RNA Poly II to pass
What are Oncohistones?
Histone modifications that affect Post translational modification level. Very specific for different tumors
