Final answer:
During DNA replication, all primers have a 5' to 3' polarity, which is crucial because DNA polymerase adds to the 3' end. A single primer is used for the leading strand, while multiple primers are needed for Okazaki fragments on the lagging strand.
Step-by-step explanation:
The polarity of each primer during DNA replication is 5' to 3', which is necessary because DNA polymerase can only add new nucleotides to the 3' end of a strand. On the leading strand, a single primer is sufficient for continuous synthesis towards the replication fork. However, for the lagging strand which is complementary to the 5' to 3' parental DNA, multiple primers are required, and the strand is synthesized discontinuously in the form of Okazaki fragments. Each Okazaki fragment is initiated with an RNA primer, which eventually is replaced by DNA nucleotides. Therefore, the primers on the lagging strand are oriented 5' to 3', pointing away from the replication fork to allow the creation of new fragments.