Here's why:
* Replication Fork: DNA replication starts at a specific point called the origin of replication and proceeds in both directions, creating a Y-shaped structure called the replication fork.
* Direction of Synthesis: DNA polymerase, the enzyme responsible for synthesizing new DNA strands, can only add nucleotides in the 5' to 3' direction. This means it can only build a new strand by adding nucleotides to the free 3' hydroxyl group of the existing strand.
* Leading Strand: One of the strands at the replication fork runs in a direction that allows DNA polymerase to continuously synthesize a new strand in the 5' to 3' direction without interruption. This is the leading strand.
* Lagging Strand: The other strand at the replication fork runs in the opposite direction, requiring DNA polymerase to work in short fragments called Okazaki fragments. This is the lagging strand.
In summary, the leading strand is the one that is synthesized continuously because its direction of synthesis aligns with the direction of the replication fork.
