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It is obvious that cell division in living organisms is now synchronised almost perfectly with DNA replication and, furthermore, the line of division has to intersect exactly the space between the two copies of all the DNA molecules in the cell. I know that as otherwise, most cells would be either empty or have a lot of excess DNA strands, which would lead to an eventual termination of replication due to scarcity of resources and energy required to trigger it.

Some theories (https://www.ncbi.nlm.nih.gov/books/NBK26876/) suggest the first protocell might have formed by a liposome simply gobbling up a self-replicating molecule. However, how would the molecule then 'know':

  1. when exactly it should replicate so that the replication coincides with the liposome diving and
  2. where in the molecule it should be located at the time of division, so that its copy ends up in a different daughter cell to itself

?

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  • $\begingroup$ I obviously don't know the answer as there isn't a proven hypothesis yet. It seems to me plausible that by chance alone (i.e. no molecular knowledge required), a small fraction of the early protocells ended up dividing with enough self-replicating material randomly spread among the two daughter cells for them to grow and repeat the duplication process until it became controlled and perfected giving those cells an evolutionary edge. $\endgroup$ – cagliari2005 Jul 4 '18 at 18:48
  • $\begingroup$ @cagliari2005 that would still be one division. In order for synchronisation to have developed, millions of synchronised replications must have taken place. $\endgroup$ – Max Jul 4 '18 at 19:23
  • $\begingroup$ Agree, but if the number of protocells is sufficiently large at each duplication phases, then while the vast majority will fail at duplicating, the few that made it will slowly evolve to perfect the mechanism (i.e. think about a population of protocells rather than single individual cells). I also wouldn't be surprised if this mechanism didn't evolve linearly but rather made several evolutionary jumps. But again, this is mere speculations and while I found the question interesting, the answer is unfortunately bound to be speculative. $\endgroup$ – cagliari2005 Jul 4 '18 at 21:20
  • $\begingroup$ @cagliari2005 I am really not sure (in fact, pretty sure that the opposite is true) such a mechanism would have any evolutionary advantage over molecules outside of the cell, if only one in many could successfully reproduce. My own theory is that at first, many molecules were able sustain themselves in one protocell, which eventually ripped apart due to excessive tension exerted by the molecules. As it did, roughly half the molecules went into one daughter cell, and half went into the other. Then, as you say, perhaps a more efficient mechanism evolved in an evolutionary jump. $\endgroup$ – Max Jul 5 '18 at 17:32
  • $\begingroup$ That is definitely a possible theory :) $\endgroup$ – cagliari2005 Jul 5 '18 at 22:00

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