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https://www.youtube.com/watch?v=27TxKoFU2Nw

In the above video it shows that during DNA replication, the lagging strand require RNA primase to add 3' -OH group for further addition of nucleotides. However, it hasn't been shown that the above strand ( leading strand) require it.

Besides, RNA is needed to initiate the polymerization because it has the 3'-OH. But when I look at the structure of deoxynucleotide, it also has the 3'-OH but it does not have the 2'-OH. So why DNA cannot initiate the polymerization?

Thanks for your answer!

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The DNA polymerase also needs a RNA primer on the leading strand to be able to start polymerization. Afterwards this is not needed anymore, since the replication goes on without a break. On the lagging strand polymerization replication can only work between the replication fork and the next region of double-stranded DNA. See the figure (from here):

enter image description here

The reason for the need for RNA primers is located in the function of the enzymes. While the DNA polymerase can only work on a double stranded template (add nucleotides to the 3'OH-end of the strand) the DNA Primase (actually an RNA polymerase) can work on single stranded targets and thus add the RNA primer there.

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  • $\begingroup$ I see! DNA primase cannot work in double stranded template. Thanks a lot. $\endgroup$ Commented Oct 17, 2014 at 11:15

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