Video narration
How do you copy DNA without losing its original information? Think of a complementary-strand exam question: you're given one sequence and work out its match. Replication uses that same rule-but first, the original strands separate. Helicase separates them by breaking the hydrogen bonds between paired bases. Each original strand acts as a template: free nucleotides pair with it, A with T and C with G. DNA polymerase joins the new nucleotides by forming phosphodiester bonds-the links in each new strand's backbone. But the originals aren't discarded: each is kept as a template for its match. That's semi-conservative replication: each new DNA molecule contains one original strand and one newly made strand. So, like completing a complementary strand in your exam, each original guides its new partner-producing two identical DNA molecules, each with one old and one new strand.