This was very cool to learn
this post was submitted on 14 Apr 2025
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Right! I've also always been blown away knowing their DNA is circular. Probably since they don't have a nucleus, but not totally sure.
It's not so much about nuclear envelope and more about ends. DNA polymerase (an enzyme that builds new DNA) cannot copy the whole end - there are a few bases that should be at the end but cannot be added. Eukaryota deal with it by a complex mechanism (they have telomeres), but it allows for multiple chromosomes and therefore larger genomes. Bacteria have a circular genome instead, a circle doesn't have an end, so they can copy as much as they need.
BTW, mitochondria and plastids, being former bacteria, also have circular genomes.