DNA Replication

• Replication copies the genetic information

• What is replication?

  • Making another copy of DNA

• When does replication take place?

  • During synthesis of interphase
  • Makes a copy of itself during mitosis and meiosis

• Why does replication happen?

  • Done in order to ensure all cells in body have same information

• Watson/Crick model gave clues to how DNA replicates

  • Base pairing rule
  • If one strand is known, the sequence of the other strand is also known
  • Therefore, a single strand of DNA can serve as a template for a new strand

• Proteins carry out the process of replication

  • Helicase (enzymes)
  • unzip double helix by breaking hydrogen bonds
  • Hold strands apart
  • DNA polymerases (enzymes)
  • Enzymes that bond free nucleotides to each template strand of DNA

• Steps in DNA replication

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  1. Double helix is opened by the enzyme helicase at the origins of replication
  • helicase breaks open the hydrogen bonds between bases
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  1. Free nucleotides are added to form base pairs according to Chargaff’s rules by an enzyme called DNA polymerase
  • 3.DNA polymerase causes the hydrogen bonds to form new rungs again and sugar phosphate bonds form to create new side
  • resulting in two new identical DNA molecules
    • Each have one original side and one new side
  • Semi-conservative replication

• Replication is fast and accurate

  • Fast:

  • 50 nucleotides added per second

  • starts at many origins of replication

  • Accurate:

  • DNA polymerase -- spell check

    • Detects and removes incorrect nucleotide
    • replaces with correct nucleotide
    • So that only 1 in every 1,000,000,000 nucleotides is wrong

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