Chromosome structure

5. Chromosome structure
 The DNA compaction problem
 The nucleosome histones (H2A, H2B, H3, H4)
 The histone octamere
 Histone H1 the linker histone
 Higher order compactions
 Chromatin loops and scaffolds (SAR)

6. Take 4 meters of DNA (string) and compact
them into a ball of 10M.– so now walk from
here to the main entrance let say 400 meters
and try to compact it all into 1 mm.

10. Nucleosomes
Histone proteins
basic (+ charged
lysine & arginine)
amino acids that
bind DNA backbone
Four core histones in nucleosome
Two of each of H2A, H2B, H3 & H4
Fifth histone, H1 is the linker histone

11. Histone amino acids lysine & arginine
proteins
H1 200-265 27% 2%
H2A 129-155 11% 9%
H2B 121-148 16% 6%
H3 135 10% 15%
H4 102 11% 4%

12. Nucleosomes

15. Compaction level
in euchromatin
Compaction level
in heterochromatin
During interphase
most chromosomal
regions are
euchromatic