Chapter 12

• DNA replication is semiconservative; the two nucleotide strands of DNA separate, and each serves as a template on which a new stand is synthesized.
• In theta replication 


  two nucleotide strands unwind, creating a replication bubble
• Within this replication bubble 


  DNA is synthesized on both strands and at the replication fork , producing two circular DNA molecules
• Rolling circle replication is initiated by a break in one strand


  It produced a 3'-OH group, two nucleotides are added while the 5' is displaced from the circle
• Bacterial DNA replication


  Initiation protein binds to the origin of replication and unwinds DNA.

  DNA Helicase attached and unwinds DNA at Replication fork

  Single Strand binding proteins prevent secondary structures

  DNA gyrase relieves strain ahead of replication fork
• Elongation:

  • Primase synthesizes RNA primers.
  • DNA polymerase adds DNA nucleotides to 3' end.
  • DNA polymerase III synthesizes new DNA on leading and lagging strands.
  • DNA polymerase I removes and replaces primers.
• Termination

  • DNA ligase seals nicks in sugar-phosphate backbone.
• Differences in eukaryotic and bacterial replication.


  Replication origins are ensured by licensing factors that must attach to the origins before commencing
• Differences part 2

  Eukaryotic nucleosomes are quickly assembled on new DNA molecules; newly assembled nucleosomes consist of a random mixture of old and new histone proteins.
• Differences part 3

  The enzyme telomerase replicates the ends of linear eukaryotic DNA molecules. The shortening of telomeres in somatic cells may contribute to aging.
• Differences part 4

  The replication process in archaea has some features in common with eukaryote replication.