Which statement best describes prokaryotic origins of replication?

• A. They typically have a single origin of replication with a defined sequence; eukaryotes have multiple origins with licensing and cell-cycle-regulated firing.
• B. They require licensing factors like ORC and Cdc6.
• C. They fire origins in S-phase via CDKs.
• D. They use telomerase to extend ends.

Answer: (A)

Prokaryotes typically start replication at one specific location on their circular chromosome, the origin of replication, which has a defined DNA sequence recognized by initiator proteins like DnaA. This single origin is sufficient for bidirectional replication around the circle. In contrast, eukaryotic chromosomes are linear and much larger, so they rely on many origins of replication. Those origins must be licensed once per cell cycle to prevent re-activation, involving factors such as ORC, Cdc6, and Cdt1 to load the helicase, and then firing is controlled by cell-cycle kinases like CDKs. Telomerase is involved in maintaining chromosome ends in linear chromosomes, not in initiating replication. So the statement that prokaryotes have a single, defined origin while eukaryotes have multiple, licensed origins best describes the difference.