Which feature describes replication initiation in terms of origin regions?

• A. Around origins forming replication bubbles with forks at borders
• B. At a single origin site with only one fork
• C. Only at the ends of chromosomes
• D. Replication occurs elsewhere without origin regions

Answer: (C)

Replication initiation happens at defined origin regions where the DNA is opened and replication begins. Once an origin is activated, helicases unwind the DNA there and two replication forks move away from the origin, creating a replication bubble with forks at its borders. In bacteria there is typically a single origin, while eukaryotic chromosomes have many origins along their length, each forming its own bubble. The ends of chromosomes, or telomeres, are handled differently and are not the sites where initiation occurs; replication must proceed from origins elsewhere and telomerase helps extend the ends after replication. So the feature described is that initiation occurs around origins, forming replication bubbles with forks at the borders.