L10 - Chromatin Modifications Flashcards
(89 cards)
Characteristics of epigentic inheritance
Change to the chromatin structure
Stable changes to gene expression
Erased in the germ line
Reversible
Characteristics of genetic inheritance
Change to the DNA base sequence
Can be repaired if recognised (e.g. nucelotide excision repair) if not recognised then they are permanent
If in a somatic cell (passed into all progeny)
If in a germ cell passed into all of the cells of the offspring
Describe the metaphor for the epigentic landscape
Like a ball (early ES cell) rolling down a hill
Series of valleys (fates_ and obstacle which the cell must overcome to reach its sepcialised cell fate
How many BP of DNA wrap around a histone
144 bp
Wrapped twice
How many subunits of the histone
8
What are the N terminal tails of the histone octomer
How do these project
2 of each: H2A H2B H3 H4
Project into free space which allows them to be modified
Describe the characteristics of closed chromatin
Concdensed
Topology makes it hard for RNA pol 2 to bind
Histones are closely associated to the DNA
Describe the characteristics of open chromatin
Sometimes dissociated from the DNA
RNA pol II able to bind
What are the 3 modifications which can be made to the chromatin
Acetylation of lysines
Mono, di, tri methylation of lysines and arginines
Phosphorylation of serines
Acetylation and methylation can both occur to which AA
Can these both occur at the same time
Lysine
No these are chemical modifications
Describe the side chain of lysine
4(CH2) - NH3
Describe how acetylation of lysine occurs
What is the name of this new structure
Final N -H(C(CH3)O)
Aceyl lysine
What enzymes add acetyl groups to lysines
What is the specificity of these enzymes
Histone acetyltransferases
Can add acetyl groups to many different lysines
What enzyme methylated lysines
What is the specificity of these enzymes
Histone methyltransferases
Exhibit equisite site specificity
What lysines/argines can be methylated of histone tail H3
H3K4 H3K9 H3K27 H3R17
What are some types of histone acetyltranferases
CREB binding protein
PCAF GCNS
What are the two code erasers (for methylation and acetylation)
Histone deacetylases
Histone demethylases
What are the two code wirters (for methylation and acetylation)
Histone acetyltransferase
Histone methyltransferase
Does acetylation cause activation or inactivation
All acetylations are activators
Does methylation cause activation or inactivation
Depends which residue is methylated
Two residues that can be methylated to activate the chromatin
H3K4 H3R17
Two residues that can be methylated to INactivate the chromatin
H3K9 H3K27
How does acetylation cause transcriptional activation
Creates a binding site for proteins with a bromodomain
Describe the bromodomain transcription activator
An epigenetic code reader
Affinity for bidning is higher when there are many resides which have been modified