A Eukaryote Without a Mitochondrial Organelle | Hacker News Reader

A Eukaryote Without a Mitochondrial Organelle

cell.com

101 pointsokket24 comments

>The complete absence of mitochondria is a secondary loss, not an ancestral feature

Basically the organism evolves to not need its mitochondria, replacing it with a different system.

The story goes that mitochondria used to be separate organisms (they have their own DNA) living in symbiosis with other cells, and eventually being subsumed.

So this would be an example of an organism similarly evolving to incorporate a bacterial symbiotic relationship (as opposed to what the mitochondria provide). Not surprising to me that this is possible, or that we eventually found something like this, given that this is how mitochondria came to exist in cells to begin with.

I was hoping that we would have found an organism that existed before mitochondria were subsumed into cells. That would be cool

It might just be that any such organism was almost immediately out-competed by anything with an internal chemical energy factory, so we never will.

IIRC, mitochondria are only used for aerobic respiration (which requires oxygen). So there might be a chance for such an organism to have survived an an anaerobic/oxygen-free environment.

That's a good point, you're right it's definitely oxygen dependent (the electron transport chain just won't work without it). Given the interest in various extremophiles, I think that if it exists we'll find it sooner or later.

To be clear, this is a lateral gene transfer from bacteria, which doesn't necessitate previous a symbiotic relationship with that bacteria, right?

I wouldn't be so sure of that part of the finding, assessing lateral gene transfer is extremely difficult - consider the situation of the tardigrade.

Mitochondria are self-contained organelles. Gene transfer would be if their DNA became part of the nuclear DNA. What you suggest is that there was first a lateral transfer, and then that transferred DNA was ejected from the nucleus, and the cell somehow formed organelles that look surprisingly like bacteria. The theory I believe is that symbiosis evolved into mutual dependency, with the mitochondria starting to live inside the cells instead of outside them sometime along the way.

Exactly. This is by far the first eukaryote known without mitochondria -- the classic case is Giardia, but like this organism it is clear that it lost them rather than being a relic of the age before endosymbiosis.

"I was hoping that we would have found an organism that existed before mitochondria were subsumed into cells. That would be cool"

Wait - isn't that what archaea is ?

Archaea are prokaryotes, not eukaryotes

I can definitely recommend "Molecular Biology of the Cell", which is a undergrad-level textbook about cells. The latest edition is always very expensive, but you can get older versions cheaply. Link: https://www.amazon.co.uk/gp/product/0815341067

I've been reading another textbook on the same topic recently, and find it endlessly fascinating. I can grok quantum mechanics intuitively on some level, because it's governed by simple mathematical laws, even if those laws are quite different from everyday experience of how physical objects work. Understanding how ordinary matter (atoms, molecules, then solids and fluids) forms out of fundamental interactions is, in principle, just a matter of solving for N variables, and you can use statistics when N gets large. But the complexity of how life exploits the precise interactions between thousands of different molecules to assemble complex machines, on scales from single proteins to whole organisms, involving thousands of interconnected feedback loops to sustain the process and counteract the large-N averaging effect of the second law of thermodynamics, is just mind-boggling.

If you're a programmer and think 10 million lines of code constitutes a complex system, reading about how cells work on a molecular level should be humbling.

If you've got a physics background, you might also enjoy Physical Biology of the Cell [0].

I haven't read it personally, so I can't vouch for it, but I've seen it recommended as one of the go-to texts for those interested in the biophysics of cells.

[0] http://www.amazon.com/Physical-Biology-Cell-Rob-Phillips/dp/...

I am reading it right now, and it is amazing how complex and sophisticated cellular dynamics are.

You can access a recent copy of Molecular Biology of the Cell through the US National Center for Biotechnology Information:

http://www.ncbi.nlm.nih.gov/books/NBK21054/

For those in search of a succinct summary of the science: http://www.sciencemag.org/news/2016/05/first-eukaryotes-foun...

FWIW — https://news.ycombinator.com/item?id=11684595

I find it funny sometimes that we bitch about genetic manipulation in weird ways, but the Random Number God (RNG) pulls this one out of it's hat and does something rather unique and surprising.

If it can be done, it will be done. Mitochondria is a pita, so sure some enterprising cell decided to figure out a way to do without it and it did.

> Mitochondria is a pita

What's troublesome about mitochondria?

Free-radicals?

https://en.wikipedia.org/wiki/Free-radical_theory_of_aging#M...

You'll get those in any respiration cycle based on oxygen.

Mixing extremely reactive substances will destroy something. It's better to just deal with it, and reconstruct whatever is damaged - the path our body tries hard to take.

Mitochondria mutates at very fast rates because of the fact that it's constantly exposed to free radicals. Apparently sexual evolution occurred because of mitochondria

"If it can be done, it will be done" suggests a rational market (or rational system) that can explore all possibilities. However, arguments for "incompetent design" strongly suggest that the system is not rational:

https://en.wikipedia.org/wiki/Argument_from_poor_design

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