ORGANIZATION OF DNA IN THE CELL
Organization of DNA in the cell
- Genome in the prokaryotes is loosely packed.
- In eukaryotes, DNA is well organized inside the nucleus.
- Levels of organization of DNA is– DNA Double helix
- Nucleosomes form of chromatin are of-
10nm chromatin fibril–
- In eukaryotics, Nucleosomes are separated by spacer DNA to which histone H1 is attached This continuous string of nucleosomes, representing beads-on-a string form of chromatin is termed as 10 nm fiber.
- DNA double helix is wrapped nearly twice (exactly 1.75 times) over a histone octamer in left-handed helix to form a disk like structure.
30nm chromatin fibril– (Solenoid)
- Groups of nucleosome form’DNA fibril’
- 6 such DNA fibrils form 30 nm chromatin fibril.
- The double stranded DNA wraps twice around a histones.
- A nucleosome associated with histone H1 is called chromatosome.
- A series of nucleosome (beads on a string) is called as polynucelosome or chromatin.
- DNA molecule is amphipathic.
- At physiological pH, DNA is negatively charged (Acidic).
- Chromatin is unfolded and uncondensed.
- Chromatin and chromosome are made up of DNA and non-histone proteins.
- At the physiological pH, DNA is negatively charged because of phosphate group.
- DNA molecule is an amphipathic.
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