Chromosomes and dna packaging
•Download as PPSX, PDF•
32 likes•17,073 views
The document discusses how DNA is packaged in eukaryotic and prokaryotic cells. In eukaryotes, DNA is wrapped around histone proteins to form nucleosomes, which are further packaged into chromatin. Chromatin exists in a "beads on a string" structure. Additional non-histone proteins help package chromatin into higher-level structures. In prokaryotes, DNA is loosely organized into loops within the nucleoid region. Eukaryotic chromatin also exists in two forms - loosely packaged euchromatin and tightly packaged heterochromatin.
Chromosomes and dna packaging
- 1. DNA Packaging HSE Zoology blog
- 2. Packaging of DNA double helix Human genome (in diploid cells) = 6 x 109 bp 6 x 109 bp X 0.34 nm/bp = 2.04 x 109 nm = 2 m/cell Diameter of nucleus = 5-10 mm HSE Zoology blog
- 4. Arrangement of DNA in a eukaryotic chromosomes • In eukaryotes, the DNA is arranged around a set of positively charged basic proteins called histones . • Histones are organized to form a unit of eight molecules called, histone octamer. • The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called nucleosome. HSE Zoology blog
- 5. DNA in a eukaryotic chromosomes HSE Zoology blog
- 8. A typical nucleosome contains 200 –bp of DNA helix. • Nucleosomes constitute the repeating unit of structure in nucleus called chromatin. • The nucleosomes in chromatin are seen as ‘beads on strings’ structure under electron microscope. HSE Zoology blog
- 10. NHC Proteins • The packaging of chromatin at higher level requires additional set of proteins called Non histone chromosomal proteins (NHC proteins) HSE Zoology blog
- 11. DNA in a prokaryotic chromosomes HSE Zoology blog
- 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 nucleoid is organized in large loops held by proteins. HSE Zoology blog
- 13. Fig. 9 HSE Zoology blog
- 14. Euchromatin and 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. HSE Zoology blog
- 15. HSE Zoology blog