Practice question

At replication fork, leading strand synthesis runs continuously toward fork movement with same polarity as unwinding. Because duplex opens progressively ahead, polymerase can track helicase without interruption. DNA polymerase requires pre-existing 3' OH for extension, supplied by primase only once at origin. Single RNA primer about 10 nucleotides synthesized by DnaG provides initial hydroxyl for Pol III, thereafter Pol III extends uninterrupted for hundreds of kilobases. Lagging strand oriented opposite cannot do this and therefore needs repeated priming generating Okazaki fragments.