L15-chromatin and gene expression Flashcards
which PTM requires energy?
acetylation
where does DNA acetylation occur?
- at AA residues of specific lysine residues at the A-terminal end
e.g H3 = K14,K23,K27,K9,K18 (IN ORDER)
e.g H4 = K16, K12,K8, K5 (IN ORDER)
THEY ARE ACYTYLATED IN A SPECIFIC ORDER = DEGREE OF ACETYLATION
what drugs/substances block histone deacetylase activity?
- Na butyrate
- Na valproate
what is the difference between AUT-PAGE and SDS-PAGE?
AUR-PAGE = MW and charge (USED TO ASSES DIFFERENT LEVELS OF CORE HISTONE ACETYLATION)
VS
SDS-PAGE = only MW
how does DNA acetylation cause the chromatin to open up?
the DNA needs to be unwraffled into the 10nm fibre using polymerases
HATs open up the chromatin in front of the TF
this causes genes to be transrcibed a the replication machinery moves in the 5’ to 3’ direction
the chromatin behind it is transcriptionally inactive and how low levels of acetylation H3 K14 AND H4 K16
THIS IS TEMPORARY AND CAN BE SWITHCED ON AND OFF
EUCHROMATIN ACTETYLATED = OPEN
HETEROCHROMATIN HYPOACTETYLATED = TRANSCIPTIONALLY INACTIVE
Which histones can have methylation? and at which AA
H3 (K4,9,27),H4 (K20) and H1 (K26)
At which lysine residues on H3 is chromatin active and also where is it inactivated?
active = high levels of acetylation and high levels of H3 K4 methylation, NO DNA METHYLATION inactive = high levels of H3 K27 methylation (trimethylated) and low acteyltion levels, DNA METHYLATED
Where are the histones phosphorylated ?
H1- at S17,169,185 and T134,151
H3 - at S10,28
Why is the position of phosphorylation important?
it alters the stability of h1 binding to the nucleosome
how can methylation and phosphorylation lead to different histone outcomes?
S10 and S29 phosphorylation both have lysine residues(K9 and K27) next to them, this causes activation and opening of chromatin
however if K9 and K27 are methylated instead = condensation and normal silencing occurs (W/ NOPHOSPHORYLATION RESIDUES)
