What is formed at the DNA replication fork?

At the DNA replication fork, a forked structure is indeed created when helicase unwinds the DNA double-helix. This is a critical step in DNA replication as it allows for the separation of the two strands of DNA, enabling each strand to serve as a template for the synthesis of a new complementary strand. As helicase moves along the DNA, it breaks the hydrogen bonds between the nucleotide pairs, resulting in the formation of the replication fork where the double-stranded DNA splits into two single strands.

This fork is essential for the action of DNA polymerase, which synthesizes new DNA strands by adding nucleotides that are complementary to the template strands. The replication fork thus serves as a dynamic site of activity where the processes of unwinding and synthesis occur simultaneously, allowing for efficient DNA replication. The other choices do not correctly describe the structure or function at the fork during DNA replication; they relate to different processes or events in molecular biology but do not pertain to the physical reality at the replication fork itself.