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From: Ernest Major <{$to$}@meden.demon.co.uk>
Newsgroups: talk.origins
Subject: Re: Life: Turn it upside down!
Date: Sat, 13 Apr 2024 10:21:39 +0100
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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?
>>>
>>> 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".
>>
>> 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