Exonuclease Activities of

DNA Polymerases

Initiation of Replication

*Strands must separate•DnaA•Helicases (DnaB and DnaC)•SSBPs (Single Stranded Binding

Proteins)•DNA gyrase (topoisomerase)

*Primase

Initiation of Replication

The sliding clamp

The two strands of a double helix are antiparallel•Continuous DNA synthesis = leading strand•Discontinuous DNA synthesis = lagging strand

DNA Synthesis

DNA Synthesis

DNA Synthesis

Completing the process

DNA Synthesis•Eukaryotes

•DNA unwinds at a replication origin •Two replication forks form •Bidirectional synthesis of DNA

•Much more DNA; complexed with proteins

•Eukaryotes have much more DNA

•Yeast 250-400 replicons •Mammalian cells up to 25,000

•Solution:

Multiple replication origins

•Yeast 4X that of E. coli •Drosophila 100X that of E. coli