DNA Replication Fork

DNA replicates semiconservatively: the double helix unwinds and each old strand serves as a template for a new complementary partner. Because DNA polymerase only synthesizes 5'→3' and the two template strands are antiparallel, one new strand (leading) is built in one continuous pass right behind helicase, while the other (lagging) can only be built backwards in short Okazaki fragments that DNA ligase later stitches together. This simulation renders that fork in real time — unwinding, both synthesis modes, and proofreading — so you can see exactly why replication needs a whole enzyme toolkit rather than a single copier.