DNA replication and transcription

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  • DNA replication and transcription
    • DNA replication
      • Semi-conservative;each new stand has one from parental helix
      • Synthesis initiated by creating a replication fork where DNA strands are separated. New strands have an antiparallel orientation.
        • Leading strand and lagging strand
          • Lagging strand requires a discontinuous backstitchingso that only 5' to 3' DNA polymerase needed
          • Requires an RNA primer sequence which is then extended by DNA polymerase and then removed by RibonucleaseH (leading)
          • For lagging, every time DNA polymerase completes a fragment, it must start synthesising a new one further along
            • Involves DNA primase synthesising short RNA primers
            • DNA ligase covalently links the Okazaki fragments
        • DNA helicase continuously unwinds the strands. Single stranded binding proteins (SSB's) maintain the single strands
    • DNA transcription
      • Initiation occurs by binding of RNA polymerase to the promoter defining starting position
        • One RNA copy produced for each reading and end dictated by specific terminator signals
        • Eucaryotes has 3 phases; Initiation, elongation and termination
          • Exons present in mRNA while introns spliced out by spliceosomes
      • RNA processing (splicing, capping and polyadenylation) all occur in cell nucleus


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