THE REPLICATION FORK - THE REPLICATION FORK In E. coli...

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THE REPLICATION FORK In E. coli circular DNA there are two simulataneous replication forks [ bi- directional replication ] Replication begins at a particular sequence known as the origin ( ori sequence ). The ori of E. coli is a sequence consisting of 245 base pairs. From start to finish, the entire chromosome is then replicated in ~ 30 minutes. An initiator protein first binds to the ORI sequence. Then, an enzyme known as helicase catalyzes the unwinding and separation of the 2 strands of parental DNA. This is an energy-requiring process which is coupled to the hydrolysis of ATP. The helicases must continually unwind the helix ahead of the advancing replication fork. Single-stranded DNA-binding proteins must then stabilize the unwound DNA by binding to the single-stranded strands and preventing them from re- hybridizing.See Figure 5.9 in text. Interestingly, short primer strands of RNA are then synthesized first by a specialized enzyme known as primase . Primase synthesizes short fragments of
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THE REPLICATION FORK - THE REPLICATION FORK In E. coli...

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