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Maintenance of genomes
• Copying the genome sequence
• Repairing damage to the genome sequence
• Rearranging genome sequences
Maintenance of genomes
• Copying the genome sequence
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Replication
Replication is semiconservative
after 1. replication
after 2. replication
Figure 15.3a Genomes 3 (© Garland Science 2007)
The Meselson-Stahl experiment
Replication is semiconservative
after 1. replication
after 2. replication
Replication
• Initiation
• DNA synthesis
• Termination
Origins of replication
Initiation of replication at oriC
Replication
• Initiation
• DNA synthesis
• Termination
DNA synthesis
Figure 15.13 Genomes 3 (© Garland Science 2007)
4-15 nt 8-12 nt ≈ 20 nt
Replication
• Initiation
• DNA synthesis
• Termination
DNA synthesis
DNA synthesis
DNA polymerases (active site)
DNA polymerases (active site)
DNA polymerases (active site)
DNA polymerases (exonuclease activity)
DNA synthesis
Figure 15.14 Genomes 3 (© Garland Science 2007)
Topoisomerases resolve tension during DNA unwinding
Figure 15.16 Genomes 3 (© Garland Science 2007)
Single strand binding proteins (SSBs) protect exposed single DNA strands
Figure 15.16 Genomes 3 (© Garland Science 2007)
Three DNA polymerase core proteins synthesize DNA simultaneously on the leading and lagging strand
In E. coli three DNA polymerase core proteins synthesize DNA simultaneously on the leading and lagging strand
Three DNA polymerase core proteins synthesize DNA simultaneously on the leading and lagging strand
Three DNA polymerase core proteins synthesize DNA simultaneously on the leading and lagging strand
Primer removalDNA polymerase I
Origins of replication
DnaA binding leads to strand separation
AAAAAAAAAAA AAA
DnaA-ATP
ORC-ATP (Origin Recognition Complex)
(6 proteins)
ORC binding does not lead to strand separation
ORC recruits cdc6 and two helicases that encircle the double-stranded DNA
Helicases
Helicase (Mcm2-7)activation
Helicases areactivated onlyin S-phase ofthe cell cycle
DNA is replicated only once per cell cycle
In bacteria re-initiation is blocked by SeqA
Finishing replicationin bacteria
Finishing replicationin eukaryotes(The end replication problem)
Protein priming insome bacteria andviruses
Extension of the ends of eukaryotic chromosomesby telomerase
Telomere binding proteins regulate telomeraseactivity and telomere length
S. cerevisiae
humans
The telomeric ends of chromosomes are protectedby proteins
