Chromatin structure and gene expression, including epigenetics Flashcards
1
Q
Describe the different states of chromatin condensation”
A
- euchromatin
- heterochromatin
2
Q
Describe euchromatin
A
- “beads on a string”
- 11nm fiber - actively transcribed genes
3
Q
Describe heterochromatin
A
- 30nm chromatin fibre of packaged nucleosomes
- extended and condensed into a mitotic chromosome
- not transcribed
4
Q
Describe the function euchromatin
A
DNA accessible for transcription
5
Q
Describe the function heterochromatin
A
DNA inaccessible for transcription
6
Q
Describe the fundamental building block of chromatin
A
Nucleosomes
7
Q
Describe histones
A
- histone octamer forms a barrel from two of each of H2A, H2B, H3 and H4
- unstable in the absence of DNA
147 bp of DNA to wrap twice around a nucleosome - “tails” of each histone monomer extend out from the nucleosome
8
Q
Describe the two major factors regulating chromatin condensation
A
- histone H1
- post-translational modifications of “histone code”
9
Q
Describe histone H1
A
- “The linker histone”
- binds to histone octamer by linker DNA, with histone tails extended out
- stabilises chromatin, increasing condensation
- important for formation of 30nm fiber
10
Q
“histone code”
A
histone tails
11
Q
Describe histone tails
A
- lots of basic residues – K and R
- positive charge at neutral pH
- when histone tails interact with DNA, more condensed chromatin
- residues can be modified by acetylation or methylation
12
Q
K
A
lysine
13
Q
R
A
arginine
14
Q
acetylation
A
removes the basic charge of K or R residue
15
Q
Describe acetylation
A
removes the basic charge of K or R residue
