DNA replication

• DNA is the ultimate director for cells and it codes for your traits
• When a cell divides, it needs to get more DNA into the new daughter cell
• DNA replication


  Making more DNA
• Where DNA replication occurs

  • In the nucleus of eukaryotic cells
  • Prokaryotic cells do not have a nucleus
• When DNA replication occurs

  Before cell division (mitosis or meiosis) in the interphase stage
• Key players in DNA replication

  • Helicase
  • DNA Polymerase
  • Primase
  • Ligase
• Helicase


  The unzipping enzyme that breaks the hydrogen bonds between DNA strands
• DNA Polymerase


  The enzyme that replicates DNA molecules and builds new DNA strands
• Primase


  The enzyme that makes RNA primers to allow DNA Polymerase to start replicating
• Ligase


  The enzyme that glues DNA fragments together
• DNA replication process


  1. DNA unwinds at the origin

  2. SSB proteins bind to keep strands separated

  3. Topoisomerase prevents supercoiling

  4. Primase makes RNA primers

  5. DNA Polymerase builds new strands

  6. Leading strand and lagging strand replication

  7. Okazaki fragments formed on lagging strand

  8. Primers replaced with DNA bases

  9. Ligase seals gaps between Okazaki fragments
• DNA replication results in two identical double helix DNA molecules from one original
• Semi-conservative replication


  Each new DNA molecule contains one old original strand and one newly made strand
• DNA Polymerase


  • Has proofreading ability to avoid making mistakes
  • Incorrect DNA base matching could lead to incorrect proteins or no proteins