Final answer:
During transcription, the bottom DNA strand base pairs with RNA nucleotides, serving as the template strand. The polymerase moves from 3' to 5', and the RNA nucleotides are joined in the 5' to 3' direction as the mRNA is synthesized. In DNA replication, the DNA polymerase synthesizes new strands in the 5' to 3' direction, creating continuous leading strands and discontinuous lagging strands.
Step-by-step explanation:
The bottom strand can base pair with the RNA molecule and thus is the template strand. The polymerase moves from 3' to 5' because the RNA nucleotides are joined in a 5' to 3' polarity. During the process of RNA synthesis, also known as transcription, the enzyme RNA polymerase reads the template DNA strand in the 3' to 5' direction, synthesizing mRNA in the 5' to 3' direction. This process involves unwinding the DNA ahead of the polymerase and rewinding it behind, creating a transcription bubble. For DNA replication, DNA polymerase adds new nucleotides only to the 3' end of the growing strand, and hence, replication proceeds in a 5' to 3' direction. The leading strand is synthesized continuously toward the replication fork. In contrast, the lagging strand is synthesized in short stretches known as Okazaki fragments, which also are laid down in the 5' to 3' direction but require multiple RNA primers.