6.2 Replication

• Purpose of DNA replication:

  • Ensures continuity of hereditary information
  • Copy genetic information before cell division
  • Allows transmission of a complete genome from one generation to the next
• DNA replication is semi conservative:

  • Double-stranded DNA molecule, each original strand serves as a template for the new strand
  • New or complementary strand pairs with one of the original strands
• Directionality of DNA molecule influences replication process:

  • DNA strand has a five prime end (phosphate terminus) and a three prime end (hydroxyl terminus)
  • Strands run anti-parallel, five prime end of one strand is opposite the three prime end of its complementary strand
  • Nucleotides can only be added in the five prime to three prime direction
  • Leading strand synthesized continuously, lagging strand synthesized discontinuously in little fragments
• Enzymes involved in DNA replication:

  • Helicase: Unwinds DNA strands
  • Topoisomerase: Relaxes supercoil at replication fork
  • DNA polymerase: Synthesizes new DNA strands, requires RNA primers to initiate synthesis, builds strands in the five prime to three prime direction
  • Ligase: Joins fragments on the lagging strand