Chromatin Structure Flashcards
How do we fold DNA in the nucleus?
Histones and nucleosomes
4 types of histones
H2A, H2B, H3 and H4
1st level of compartmentalisation
beads-on-a string nucleosome array
Histone H1
Role of bringing together the 2 extremes that are coming out from the nucleosome
2nd level of compartmentalisation
Done by non-histone chromosomal proteins 1:1:1 [DNA: proteins: non-histone proteins]
Chromatin composition
DNA: histones: non-histone proteins
Different forms of chromatin
Euchromatin
Heterochromatin
Euchromatin
Displays a dispersed state marked by weak binding of histone H1: coding genes are found here
Heterochromatin
Associated with tight histone H1 binding and remains highly condensed: non coding genes found here
classes of heterochromatin
- Constitutive heterochromatin
- Facultative heterochromatin
Constitutive heterochromatin
Remains condensed and is genetically inactive at all times and in different tissues
Facultative heterochromatin
Sometimes genetically inactive and sometimes active depending on stimuli
Where is the gene-rich part of the genome found?
In the center of the nucleus: high levels of expression
Where is the gene-poor part of the genome found?
located towards the nuclear envelope: low levels of expression
