Maintenance of genomes Copying the genome sequence Repairing damage to the genome sequence Rearranging genome sequences

Maintenance of genomes Copying the genome sequence = 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 Genomes 3 (© Garland Science 2007) 4-15 nt8-12 nt≈ 20 nt

Replication Initiation DNA synthesis Termination

DNA synthesis

DNA polymerases (active site)

DNA polymerases (exonuclease activity)

DNA synthesis

Figure Genomes 3 (© Garland Science 2007) Topoisomerases resolve tension during DNA unwinding

Figure Genomes 3 (© Garland Science 2007) Single strand binding proteins (SSBs) protect exposed single DNA strands

Figure 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 removal DNA polymerase I

Origins of replication

DnaA binding leads to strand separation A A A A A A A A A A A A A A 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 are activated only in S-phase of the cell cycle

DNA is replicated only once per cell cycle

In bacteria re-initiation is blocked by SeqA

Finishing replication in bacteria

Finishing replication in eukaryotes (The end replication problem)

Protein priming in some bacteria and viruses

Extension of the ends of eukaryotic chromosomes by telomerase

Telomere binding proteins regulate telomerase activity and telomere length S. cerevisiae humans

The telomeric ends of chromosomes are protected by proteins