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•  Nucleosomes help to supercoil the DNA

In eukaryotic organisms, the DNA is packaged with histone proteins to create a compacted structure called a nucleosome

  • Nucleosomes help to supercoil the DNA, resulting in a greatly compacted structure that allows for more efficient storage
  • Supercoiling helps to protect the DNA from damage and also allows chromosomes to be mobile during mitosis and meiosis

Organisation of Eukaryotic DNA

  • The DNA is complexed with eight histone proteins (an octamer) to form a complex called a nucleosome
  • Nucleosomes are linked by an additional histone protein (H1 histone) to form a string of chromatosomes
  • These then coil to form a solenoid structure (~6 chromatosomes per turn) which is condensed to form a 30 nm fibre
  • These fibres then form loops, which are compressed and folded around a protein scaffold to form chromatin
  • Chromatin will then supercoil during cell division to form chromosomes that are visible (when stained) under microscope

Organisation of DNA

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•  Utilisation of molecular visualisation software to analyse the association between protein and DNA 

    within the nucleosome

A nucleosome consists of a molecule of DNA wrapped around a core of eight histone proteins (an octamer)

  • The negatively charged DNA associates with positively charged amino acids on the surface of the histone proteins
  • The histone proteins have N-terminal tails which extrude outwards from the nucleosome
  • During chromosomal condensation, tails from adjacent histone octamers link up and draw the nucleosomes closer together

To view the structure of a nucleosome via an interactive pop-up, click on the name of the structure below:

nucleosome diagram