Nick Lane: belief

Transcript context

…It kind of makes me wonder whether we’re, because we’ve only observed one way to solve this solution, we’re assuming that there must be only one way to solve the problem. The problem itself doesn’t seem… You just want a smaller copy of the genome sitting next to the site of respiration. That’s the basic problem. There’s no other way to solve that? Maybe there is, but I think we have to look at the probability of certain things happening. If you want to have a giant bacterium, there are a bunch of giant bacteria around on Earth. There’s at least six or seven different, quite unrelated species that have evolved giant size. The thing that they all have in common is they have what’s called extreme polyploidy, which is to say they have literally tens of thousands of copies of their complete genome. So it may be a small genome, we’re talking a three-megabase genome, so around 3,000 genes in it. And you’ve got tens of thousands of copies. Sometimes the very largest ones have 700,000 to 800,000 copies of their complete genome. The energy requirements for copying all of that and expressing all of those genomes are colossal. What we have with endosymbiosis, we still have extreme polyploidy, but we’ve whittled away all the genes that you don’t need. A symbiosis is based on effectively complementarity. You’ve got a symbiont that’s doing something for the host cell and the host cell that’s taking something or giving something back to the endosymbiont. So it’s a relationship which is based on mutual needs. One of them becomes much smaller and that allows the other one to become much larger. So a symbiosis will do it. Now there could be multiple ways of having a symbiosis, but there’s no examples of it. All of these examples of very large bacteria and they all have extreme polyploidy. None of them have come up with a complex trafficking network where you effectively take things in and you ship it over there. There’s just not enough genetic space. But just to make sure I understood the feature request correctly, it’s basically: you want a smaller copy of the genome that is only relevant to respiration sitting across the entire membrane, and many copies of it sitting across the entire membrane. I guess I’m just, it seems hard for me to……

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