Chromatin Structure
Chromatin...txn
inhibits
does histone methylation influence chromatin structure?
no as it doesn't affect lysine charge
Core histones form repeating units called...
nucleosomes
Chromatin is composed primarily of...
(small basic proteins) histones (core histones and linker histones)
How does acetylation mediate transcriptional activation? (2 ways)
1) (acetylation) reduces (lysine's) positive charge so there's less binding between histones and -ve DNA phosphate backbone so chromatin is disrupted/opened up. 2) specific acetylated lysine residues (in histones) are recognised by proteins with bromodomains; protiens with bromodomains often promote txn.
How are nucleosomes organised in terms of linker histones and fibre thickness
DNA passing from one nucleosome to the next - 10nm fibre Linker histones like histone H1 bind to the DNA between nucleosomes 30nm fibre is formed
Different types of histones are...
H2A H2B H3 H4
Which enzymes are responsible for the acetylation (and de-acetylation) of lysine in histones?
HATs (histone acteyl transferases) and HDACs (histone deacetylases)
Which enzymes carry out methylation of histones? What kinds o methylation can be done?
HKMTs (histone lysine methyl transferases) mono, di, tri (methylation) (methylation isn't readily reversible)
The main two post-translational modifications of histones are...
acetylation methylation
Where do HATs bind?
activators
Basic function of chromatin is to...
compact DNA
how does methylation of the lysine in histones control txn?
specific methylated lysines are recognised by specific proteins, and so act as activating or repressing marks
what happens to nucleosomes during txn activation?
they are disrupted or lost
how do histone variants modulate chromatin structure?
they confer a novel structure and functional properties of the nucleosome which affect the chromatin dynamics (H4 doesn't have a variant though!)
Describe a nucleosome in terms of the amount of DNA to histones and the different types of histones
~147bp of DNA wrapped around an octamer of histones Octamer = central H3-H4 tetramer + 2 flanking H2A-H2B dimers