So I’ve been enjoying videos from Kurzgesagt and one in particular points to the valuable molecule ATP and I remember it from biology (https://youtu.be/QImCld9YubE). So while this talks about the very beginning of multicellular organisms I’ve never understood how an organism can absorb another and then make DNA so both organisms are created going forward.
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I’m assuming you’re asking about the endocytosis theory for the origination of mitochondria and chloroplasts. Both mitochondria and chloroplasts have plasmid DNA, which is a circular DNA molecule that bacteria and other prokaryotes use instead of the linear DNA molecules eukaryotes use. Each plasmid has something called an origen of replication, which is a gene that control replicating that plasmid. The origins of replication in both mitochondria and chloroplasts are unique to those organelles, and don’t work with the same DNA replication machinery we use to replicate our DNA. Instead, the mitochondria and chloroplasts take care of DNA replication themselves!
So, short answer, the original organisms wouldn’t replicate both sets of DNA!
Kurzgesagt is awesome.
Well a lot of early evolution is still being sussed out. There are a lot of ways that the process could have happened, but what actually happened might be lost to time. The jump from single-cells to multiceullar life took a REALLY bloody long time. (And it’s a generally good idea and has independently happened multiple times). We’re talking [an astronomically long time](https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life). 3/10th the lifecycle of a typical star.
Organisms eating other organisms happens all the time and is a pretty concept.
Taking DNA into oneself has the possibility of something happening with that data. Less so for humans and such because we drop it into a vat of acid down there, but single-celled organisms have their metaphorical stomach in the same place as where they keep their own DNA. Generally “inside the membrane”. Once inside, if it starts replicating itself, that’s a virus. If it breaks down into amino acids, that’s food. If it does something useful, maybe the host cell keeps it around and starts letting it replicate at least once.
Consider the horrifying [cymothoa exigua](https://en.wikipedia.org/wiki/Cymothoa_exigua) which replaces a fish’s tongue. It’s a separate organism that slips in and takes up residence. Somehow it replicates and makes more of itself. Given time maaaaaaybe the host fish will get more involved with helping with the reproduction and getting into other fish’s mouths.
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