DNA packaging

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  • Created by: Ellie0o0o
  • Created on: 27-04-15 15:39
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  • DNA Packaging
    • Chromatin
      • Euchromatin
        • Loosely packed
        • Replicated early in the S phase
        • Found in nucleus centre
      • Heterochromatin
        • Replicated later
        • Tightly packed
        • Found at the nucleus periphery
        • Tends to hold oncogenes, telomeres, centromeres and transposons
    • "Beads on a string"
      • A series of nucleosomes
        • = 4 histone proteins + 146bp DNA
          • Histone
            • Octamer
              • Monomers are...
                • Small: 100-140 aas
                • 2x H2A
                • 2x H2B
                • 2x H3
                • 2x H4
                • BASIC
                  • A partial +ve charge allows DNA association
            • H1
              • Linker histone, joins nucleosomes
    • 30nm Fiber
      • Beads on a string further compacted
      • Formed by H1 linking nucleosomes
    • Though levels of packaging vary, naked DNA is rare
      • It signals a problem such as viral DNA
      • The less packaged the DNA, the more vulnerable it is to DNase
    • Additionally affected by
      • Histone modifications
      • Chromatin remodelling complexes
      • DNA methylation
    • Packaging is a major difference between pro- and eukaryote DNA
      • No packing mean no block to transcription

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