DNA Replication Practice Test

At the replication fork, the double helix is unwound and both strands are copied by DNA polymerases. One strand is made continuously in the direction of the fork (the leading strand), while the other is copied in short, discontinuous pieces (Okazaki fragments) on the opposite template. Primers are laid to start synthesis, and as fragments are formed on the lagging strand, they are extended by polymerases and eventually joined together by ligase. This coordinated action—unwinding, primer placement, continuous synthesis on the leading strand, fragmentary synthesis on the lagging strand, and ligation of fragments—best describes what happens at the fork. The other options are incomplete or incorrect: transcription uses RNA polymerase, not for genome replication; ligase does not initiate replication at the origin; and only copying the leading strand misses the essential lagging-strand process.