What happens at a DNA replication fork during replication?
DNA strand separation.
Enzymes that synthesize new DNA (polymerases) use a single strand of DNA. However, DNA is double stranded and thus requires separation before the polymerases can start replicating DNA.
This seperation of strands happens at the so called replication fork. Special enzymes, helicases form the replication fork by breaking the hydrogen bonds between the strands and unwinding the DNA helix.
A number of helper proteins assist the helicase in keeping the strands apart, allowing polymerases to bind and start the replication.