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).

Exam Important

  • 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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