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

On Fri, 11 May 2007 14:41:21 +1000, j.wilkins1@xxxxxxxxx (John
Wilkins) wrote:

Perplexed in Peoria <jimmenegay@xxxxxxxxxxxxx> wrote:

"John Wilkins" <j.wilkins1@xxxxxxxxx> wrote...
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.

I do not see why it has to be fermentation. If you have a lysed membrane
then whatever are the contents of that vesicle will be biologically
valuable, whether sugars or whatever. Since we are postulating
relatively primitive systems, it's likely that the intake of food
particles will be by vesicles forming on the membrane that transport
material internally, so they will almost certainly - some of them -
subsist on processed polymers from other organisms.

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.

Maybe. Organic material will denature into oligomers that are
functionally indistinguishable from abiotic organic molecules that are
of high energy or substrate-material value.

Suppose there are protobionts that routinely die in the environment, and
thus release their material, or are even predated by some simple system
that can lyse lipid membranes. The entropy of those molecules released
will be valuable to some systems, and selection will rapidly drive them
to become eficcient at it. No matter how far back you go, there has to
be an ecological web.

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 don't see why almost all molecules that are ingested have to be lipids
(although I can see how free-floating lipids in a medium might be
valuable to the formation of the predator's membranes).

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.

I've been largely incommunicado for the past week myself...

The earliest true biological organism must have been a very
sophisticated device filled with complex (but not irreducibly so)
machinery. To meet the definition, it must have had a molecular
biology that used genetic information both to construct and to
duplicate itself. There must have been an enormous amount of prior
"evolution" of this machinery in protocells. At the same time, the
earliest true biological organism must have had a biochemical
metabolism, both catabolic to use chemicals as a source of energy and
anabolic to use chemicals as substrates for building its own
structure. Again there must have been an enormous amount of prior
"evolution" of this machinery. And the earliest true biological
organisms must also have had cell biological functions of transport
and responsiveness to the environment, also required a lot of prior
"evolution". So the earliest true organism "ate" whatever those
protocells ate including the protocells themselves using the existing
machinery. At some point in the process, it was obviously necessary
to ensure that autotrophic protocells maintained themselves in the
environment in sufficient quantity to drive the entire system, quickly
becoming incorporated into the early true cells themselves. The only
question is whether that piece was necessarily part of the very first
true cell if there were enough protocellular autotrophs already
available.

The details are rather less important. Whether fermentation as we now
know it or some other biochemical process was the major energy
providing pathway is irrelevant; the protocell chemistry developed
some pathway that was effective. Glycolysis seems very likely since
it is so widespread in modern forms and anaerobic metabolism seems
necessary since free oxygen was lacking. However the early protocell
metabolism must have been capable of dealing with a wide variety of
chemicals both as energy sources and for synthesis, perhaps through
the expediency of developing tools to reduce just about any complex
molecule to a relatively small set of simple organic building blocks.

The membrane transport problem also necessarily had to have been
already solved by the protocells so that the earliest cells already
had the ability to incorporate molecules that were not lipid soluble.

In other words, the problem is pushed back one step. The earliest
organisms used existing machinery to solve their problems of living.
The problem is how the separate pieces of machinery developed;
pieces of metabolism in this entity, pieces of membrane function in
that one, genetic mechanisms in a third, all capable of merging and
separating and thus sharing the accumulating techniques of how to
manage it all. Since energy drives the whole process, autotrophy in
the sense of taking some "inorganic" form of energy to build organic
chemistry must have been present from the outset.






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Relevant Pages

  • Re: What did the first single-celled organisms eat?
    ... No, seriously, they had to have some source of energy and carbon. ... molecules, some of whose energy can be extracted. ... Original organisms probably evolved as a community that was overall ... And developing the machinery for discriminating useful foreign ...
    (talk.origins)
  • Re: Lets be more exact.
    ... does the energy come from. ... > Why would an RNA replicator or any replicator need protein? ... molecules that "need" it by the self-organizing properties of membranes ... situation as with reproducing organisms. ...
    (sci.bio.evolution)
  • Re: What did the first single-celled organisms eat?
    ... molecules, some of whose energy can be extracted. ... Original organisms probably evolved as a community that was overall ... If you have a lysed membrane ... Also, I'm assuming that almost all early biomolecules were lipids, and it ...
    (talk.origins)
  • Re: What did the first single-celled organisms eat?
    ... No, seriously, they had to have some source of energy and carbon. ... many inorganic processes that make high-energy molecules, ... That leaves somehow absorbing whole molecules to become self-biomass. ... and insert it into your own membrane. ...
    (talk.origins)
  • Re: What did the first single-celled organisms eat?
    ... molecules, some of whose energy can be extracted. ... If you have a lysed membrane ... that can lyse lipid membranes. ...
    (talk.origins)