Which statement is true about origins of replication in prokaryotes and eukaryotes?

Which statement is true about origins of replication in prokaryotes and eukaryotes?

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

Answer: (A)

Origins of replication determine where DNA synthesis begins. In prokaryotes with a circular chromosome, replication starts at a single origin and proceeds bidirectionally until the entire genome is copied. In contrast, eukaryotic chromosomes are long and linear, so many origins fire during S phase, creating multiple replication forks that collectively copy the whole chromosome efficiently. This is why the statement about prokaryotes having a single origin per chromosome and eukaryotes having multiple origins per chromosome is the best description. The other ideas don’t fit because prokaryotes generally don’t use multiple origins, eukaryotes don’t rely on a single origin per chromosome, origins aren’t per gene, and replication isn’t restricted to telomeres alone in eukaryotes.

Origins of replication determine where DNA synthesis begins. In prokaryotes with a circular chromosome, replication starts at a single origin and proceeds bidirectionally until the entire genome is copied. In contrast, eukaryotic chromosomes are long and linear, so many origins fire during S phase, creating multiple replication forks that collectively copy the whole chromosome efficiently.

This is why the statement about prokaryotes having a single origin per chromosome and eukaryotes having multiple origins per chromosome is the best description. The other ideas don’t fit because prokaryotes generally don’t use multiple origins, eukaryotes don’t rely on a single origin per chromosome, origins aren’t per gene, and replication isn’t restricted to telomeres alone in eukaryotes.