How does the origin of replication differ between prokaryotes and eukaryotes?

• A. Prokaryotes have multiple origins per chromosome; eukaryotes have a single origin per chromosome.
• B. Prokaryotes have origins per gene; eukaryotes origin per chromosome.
• C. Prokaryotes replicate at a fixed origin; eukaryotes at telomeres only.
• D. Prokaryotes have a single origin per chromosome; eukaryotes have multiple origins per chromosome.

Answer: (D)

Origins of replication are the starting points for copying DNA. Prokaryotes typically have a single origin on their circular chromosome, and replication proceeds bidirectionally until the whole chromosome is duplicated. This simple setup fits the small, circular bacterial genome and allows a tightly coordinated copy during the cell cycle.

Eukaryotes, on the other hand, have linear chromosomes that are much larger and densely packed into chromatin. To copy all DNA efficiently within the S phase, many origins of replication are spread along each chromosome. These multiple origins fire to create several replication forks that proceed in parallel, accelerating replication across the long genome. Telomeres are an important feature of linear chromosomes but are not the sole sites where replication starts.

So, the best description is that prokaryotes have a single origin per chromosome, while eukaryotes have multiple origins per chromosome.