DNA Replication

• Semi-Conservative DNA Replication:

  • occurs during S phase of interphase
  • requires ATP
  • enzymes needed:
  • helicase to break H bonds to separate 2 DNA strands
  • DNA polymerase to synthesise a new strand of DNA (in the 5' to 3' direction), to catalyse the formation of phosphodiester bond, and proofreads DNA
  • DNA ligates to join DNA fragments together and catalyse the formation of phosphodiester bonds
• Steps of DNA Replication:

  1. DNA double helix unwinds
  2. Helicase break H bonds - 2 DNA strands are separated, both strands are used as templates
  3. Free, activated DNA nucleotides are activated with 2 additional phosphates - have 3 phosphate groups in total, the bases of activated nucleotides form H bonds with bases on each exposed parent DNA strands
  4. DNA polymerase attach to each of the two separated parental strands - catalysing the formation of a new strand of DNA, DNA polymerase links activated nucleotides together by removing 2 phosphate groups, catalysing phosphodiester bonds formation
• One DNA strands is synthesised continuously, called the leading strand, the other is synthesised in sections known as Okazaki fragments, and is called the lagging strand, the fragments are joined by DNA ligase