In prokaryotes, about 1,000 nucleotides can be copied per second, so all of the 4.7 megabytes of Escherichia coli can be copied in about 40 minutes. Since the eukaryotic genome is immense compared to the prokaryotic genome, one might think that the eukaryotic DNA replication would take a very long time. However, actual measurements show that the chromosomes in eukaryotes have multiple replication sites per chromosome. Eukaryotic cells can replicate about 500–5,000 bases per minute; the actual time to copy the entire genome would depend on the size of their genome.