Answer
DNA nucleotides are used as PCR primers, allowing for end replication that’s not possible inside a cell.
Work Step by Step
DNA polymerase runs 3’ to 5’ on the template strand, creating a strand 5’ to 3’. It cannot act independently on the 5’ end of a strand. In the cell, this means an RNA primer sits at the 5’ end of the new strand and cannot be revised later by DNA polymerase. This issue is circumvented in PCR by using DNA nucleotides as primers.
