Final answer:
DNA polymerase III builds the DNA strand in the 5' to 3' direction during replication. The leading strand is synthesized continuously towards the replication fork, while the lagging strand is built in short segments called Okazaki fragments away from the fork.
Step-by-step explanation:
DNA polymerase III (DNA pol III) builds a new DNA strand by adding nucleotides only in the 5' to 3' direction. This is because, during DNA replication, the enzyme requires a free 3'-OH group to add nucleotides to a growing DNA strand. Due to the antiparallel nature of DNA, issues arise at the replication fork because only one strand, the leading strand, can be synthesized continuously in the direction towards the replication fork, mimicking the movement of the replication machinery.
On the other strand, known as the lagging strand, DNA synthesis is discontinuous. Short segments called Okazaki fragments are built in the direction away from the replication fork. Each Okazaki fragment begins with a primer, which provides the required 3'-OH group, and is then extended by DNA polymerase III; however, this requires the enzyme to frequently restart the synthesis process as the replication fork progresses.
The complex process of DNA replication is orchestrated with intricate precision, ensuring that both strands are elongated simultaneously despite their opposite orientations relative to the replication fork's movement. The leading and lagging strands are cohesively synthesized, with the replication fork typically moving at an astonishing rate of 1000 nucleotides per second.