Modes of Replication

Following Meselson and Stahl's work, investigators confirmed that other organisms also use semiconservative replication. No evidence was found for conservative or dispersive replication. There are, however, several different ways that semicon-servative replication can take place, differing principally in the nature of the template DNA—whether it is linear or circular—and in the number of replication forks.

Individual units of replication are called replicons, each of which contains a replication origin. Replication starts at the origin and continues until the entire replicon has been replicated. Bacterial chromosomes have a single replication origin, whereas eukaryotic chromosomes contain many.

Theta replication A common type of replication that takes place in circular DNA, such as that found in E. coli and other bacteria, is called theta replication (I Figure 12.4a), because it generates a structure that resembles the Greek letter theta (0). In theta replication, double-stranded DNA begins to unwind at the replication origin, producing single-stranded

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