Dna packaging

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1. DNA Packaging

2. Packaging of DNA double
helix
Human genome (in diploid cells) = 6 x
10
9
bp
6 x 10
9
bpX 0.34 nm/bp= 2.04 x 10
9
nm
= 2 m/cell
Diameter of nucleus = 5-10 mm

4. Arrangement of DNA in a eukaryotic
chromosomes
• In eukaryotes, the DNA is arranged around a
set of positively charged basic proteins
called histones.
• Histonesare organized to form a unit of eight
molecules called, histoneoctamer.
• The negatively charged DNA is wrapped
around the positively charged histoneoctamer
to form a structure called nucleosome.

5. DNA in a eukaryotic
chromosomes

8. A typical nucleosomecontains 200 –bpof DNA
helix.
• Nucleosomesconstitute the repeating unit of
structure in nucleus called chromatin.
• The nucleosomesin chromatin are seen as
‘beads on strings’ structure under
electron microscope.

10. NHC Proteins
• The packaging of chromatin at higher
level requires additional set of proteins
called Non histone chromosomalproteins
(NHC proteins)

11. DNA in a prokaryotic
chromosomes

12. Prokaryotic cells lack a nuclear membrane
and defined nucleus, even though DNA
is not scattered throughout the cell.
• DNA, being negatively charged is held
with some proteins having positive
charges in a region termed as nucleoid.
• The DNA in nucleoidis organized in
large loops held by proteins.

13. Fig. 9

14. Euchromatinand
heterochromatin
Euchromatin
In a typical nucleus, some regions of chromatin
are loosely packed and lightly stained known as
euchromatin. This region contains active
chromatin.
Heterochromatin
The chromatin that is more densely packed and
stains dark are called heterochromatin. This
region contains inactive chromatin.