TMC 3- Chromatin structure Flashcards
hat does DNA in eukaryotes predominantly exist as
Chromatin
length of DNA in the human nucleus,
2 m
number of histones in a nucleosome
8 (histone octamer)
how many core histones – what are they
4 core and 1 linker
Core - H2A, H2B, H3+H4
Linker - H1
Linker histone
H1
nucleosome
formed by ~146bp of DNA + histone octamer
what are the dimers formed in an octamer
H2A & H2B
H3 & H4
Where does H1 histone bind and function
binds to the linker DNA and induces tighter DNA
wrapping around the nucleosome and compacts DNA further
chromatin.
The complex of nucleosomes, H1 transcription factors and other proteins is called chromatin.
2 main functions of chromatin
1) compaction and organisation of DNA
2) regulation of gene expression.
nucleosome structure
what is a major protein in the scaffold.
Topoisomerase II
Chromatin organisation
DNA coiled around histones giving beads on string structure – 10 nm fibres
Beads on string structure can be condensed into 30nm fibres
This compacts the DNA 40x
Chromatin– the 10nm and 30nm fibres together w/ their associated proteins is called chromatin
Chromatin organised in loops around a protein scaffold
Topoisomerase II is a major protein in the scaffold
During mitosis and meiosis DNA further compacts into chromosomes about 10,000-20,000 x
what is a nucleosome bead made of
- Histone octamer:
–> 2 H2A (histone 2A)
–> 2 H2B
–> 2 H3
–> 2 H4 - DNA coiled around it
*** Linker histone - H1 IS NOT PART OF THE BEAD BUT IS A KEY COMPONENT OF CHROMATIN
Is H1 histone a part of the nucleosome bead
no.
but is a key component of chromatin
it binds to the bead wround the DNA enters and exits
**H1 can stabilize both nucleosome structure and higher-order chromatin architecture
charge on histones
+ve
(also v. abundant and highly conserved)
What part of the histone differs btwn each one
and can be modified extensively
The N-terminal tail
an N terminal tail that differs between the
histones - this tail is exposed on the histones and
can be modified extensively
what is the histone fold region made up of
three alpha helical regions
a common histone fold region made up of three
alpha helical regions
what do histones contain?
an N-terminal tail (differs btwn histoned - can be highly modified)
A common histone fold region
A relatively short C-terminal tail
similarities and diff btwn histone structures
The main bodies (histone fold) of the core histones – similar structure – 3 alpha helical regions and 2 short loops
N-terminal tails of histones differ from each other – can be modified extensively
main N-terminal tail modifications that occur are?
main N-terminal tail modifications that occur are?
main N-terminal tail modifications that occur are?
main N-terminal tail modifications that occur are?
