Re: Life: Turn it upside down!

On 11/04/2024 14:41, Arkalen wrote:

I agree those are much more similar than I'd been thinking; I was thinking of viruses as they are outside of the cell but you're right that when you consider their activity inside of the cell then there's much less reason to say that activity isn't "metabolism". Except for that whole "meta" part of "metabolism" : does mimivirus do catabolism? Do intracellular parasites?
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I'll look it up after posting but I notice you point out the difference that intracellular parasites have their own cytoplasm. I will hazard the guess that this means they have their own *membranes*, and further hazard the guess that they use respiration to generate a proton motive force across that membrane to regenerate ATP. I could see it if they didn't, after all they can get ATP from the host cell can't they. But if they do, that would be metabolism with the "meta".

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Microsporidia have lost the ability to generate their own ATP. The same is said of Giardia.

 Do you have a cite on that? This paper suggests that Giardia does have metabolism, using fermentation (but then maybe it varies by Giardia species, this paper seems to be looking at one specific one):
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC88984/
 It explicitly describes it as generating its own ATP unless I'm seriously missing something:
 "However, certain eukaryotes, including Trichomonas spp., Entamoeba spp., and Giardia spp., are characterized by their lack of mitochondria and cytochrome-mediated oxidative phosphorylation. They rely on fermentative metabolism (even when oxygen is present) for energy conservation. Glycolysis and its brief extensions generate ATP, with generation dependent only on substrate level phosphorylation."
 

I'd misinterpreted this, by not paying sufficient attention to the context of a statement "but there is no ATP production".
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8404698/
In my defence, your mention of respiration above distracted me from considering non-mitochondrial (non-respiratory) ATP production. Not all intracellular parasites act as you proposed, but I overstepped the mark in baldly stating that they don't produce ATP.
--
alias Ernest Major