Re: What did the first single-celled organisms eat?


"John Wilkins" <j.wilkins1@xxxxxxxxx> wrote in message news:1hxwifa.1hn0hj8emoyzkN%j.wilkins1@xxxxxxxxxxxx
Perplexed in Peoria <jimmenegay@xxxxxxxxxxxxx> wrote:

"John Wilkins" <john@xxxxxxxxxxxxx> wrote...
John Harshman wrote:
snex wrote:

On May 9, 12:25 pm, Terry <Kilow...@xxxxxxxxxxx> wrote:

What did the first single-celled organisms eat?

each other.

They lost money on every deal, but they made it up in volume?

No, seriously, they had to have some source of energy and carbon. There
are many possibilities, some of which are still working today. There are
many inorganic processes that make high-energy molecules, some of whose
energy can be extracted. Currently living bacteria make use of all of
them. Look up, for example, "chemautotroph".

Original organisms probably evolved as a community that was overall
autotrophic. It is speculated (for we cannot know for sure) that they
worked off volcanic flows containing H2S, but I am betting that they
would happily reuse each other's high entropy molecules as well if they
could.

And I am betting that they would if they could, but they couldn't.

Why?

Well, using foreign molecules for energy doesn't make sense to me for the
early days because my biochemical intuition says that getting useful
energy by fermentation takes some pretty sophisticated enzyme-like
machinery. Doing that came later.

That leaves somehow absorbing whole molecules to become self-biomass. Sure,
that saves some kind of metabolic effort if the molecule you absorb is
something you would have needed to make anyways. But consider that absorbing
it is probably a mistake if it is not one of the molecules normally made
by your biochemistry. It may gum up your operations. So, it is only safe
and advantageous to absorb the molecule if it came from an unfortunate
member of your own 'species'. But if you think about it, that defeats the
whole reason why you postulated that they all evolved as a community.
And developing the machinery for discriminating useful foreign molecules
from the unuseful ones is also something that my intuition tells me must
have come much later. Simple inorganic foodstuffs are much easier to
'recognize' and use in the right way.

Also, I'm assuming that almost all early biomolecules were lipids, and it
is not easy energetically to pull a lipid molecule out of one membrane
(even a 'dead' one) and insert it into your own membrane. And fusing
your membrane with that of another organism runs into the same issue
of "same species, safe but ecologically pointless; different species, unsafe".

I apologize that this response has taken so long to appear (if it HAS
finally appeared!) ... Hey, why am I apologizing? It ain't my fault that
my ISP (AT&T) is technically incompetent at telecommunications.

.

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