Biology as Poetry: Genetics

Bacteriophage Ecology Group

Origin of Replication

Specific sequence on a DNA molecule at which replication forks are initiated.

While bacterial chromosomes as well as plasmids tend to have only a single origin of replication, the chromosomes found in eukaryotic cells tend to have multiple origins of replication. This difference reflects especially the tendency for eukaryotic chromosomes to be much larger than bacterial chromosomes. DNA replication in eukaryotes thus can proceed in multiple locations in parallel, resulting in much sooner completion of the task than would be the case were these chromosomes to possess only a single origin or replication.

Note that, upon initiation, replication forks open in two, opposite directions rather than just one. It is the norm thus for DNA replication to proceed in two different directions simultaneously.

Note also that though RNA priming occurs repeatedly in association with the replication of lagging strands, the initiation of Okazaki fragments does not occur at origins of replication in the same sense as the initiation of replication forks. On the other hand, the replication of leading strands – since leading strands are primed only once – is indeed initiated in conjunction with origins of replication.

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