Re: Life's range = 0-50C


You're correct in showing criticism for the hyperthermophilic origin
of the LCA. Truth is that the first dividing cell may have been a
mesophile. However, given how deeply rooted thermophiles are in the
tree of life, I feel its better evidence than the contrary. It is
also good to note that many enzymes using metal cofactors are also
highly divergent and well rooted. Since there is a high concentration
of metal ions around deep sea volcanic vents, this seems to point us
toward that location for the origin of life. To make a terrible
metaphor, I can just see in my minds eye a sea of thermodynamic and
reduction/oxidation energy around deep sea vents as being favorable
for the first enzymes to ride the free energy roller coaster.

I have not read deeply into spontaneous polymerization, but it is
possible under some laboratory conditions, and there are references in
the composomes paper that I sited earlier. It's curious seeing a
trade off here- RNA's h-bonds are too unstable at high temperatures,
yet any kind of genetic templating cannot occur without RNA (or
possibly not?), and proteins are indeed more stable, and yet cannot
systematically self clone themselves amino acid per amino acid. How
did these two interact in the LCA?

I know some thermophilic spp., such as Aquifex and Thermatoga, have a
high GC content in their genomic sequences to keep stable, but I'm not
sure the same is true of RNA's. I've tried looking on pubmed for a
study showing some kind of stabilizing structural trend across
temperature for RNA aptamers, tRNAs and riboswitches, or any kind of
comparison between thermophilic and mesophilic RNAs. What I've heard
(from the graduate student I used to work under) is that RNA's with
some enzymatic function simply have a shorter lifetime before being
degraded in thermophiles. If you know a review on this, (please
anybody) point me to a reference.

Now, here are some interesting points to explore! I'm sure comparable
RNA sequences or structures are available. Comparing, say, mesophilic
tRNAs with a thermophilic ones this would make a great review
article. Another interesting point to explore is how ribosomes and
the RNA at the site of thermophilic DNA polymerases are able to remain
functional and stable. Do proteins stabilize them? Is there RNA at
all in a thermophilic polymerase? I don't think PCR polymerases have
any, so I doubt it. I'll explore this more!

[You are quite right about being overly snippy. However, just reading
the phrase 'does anybody disagree?' at the end of an obviously
incorrect litany of claims was the straw that snapped the Camel's
back.]




On Jun 29, 12:33 pm, "Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx>
wrote:
<Jeremy.Winfi...@xxxxxxxxx> wrote in messagenews:f5u870$2euo$1@xxxxxxxxxxxxxxxxxxxxxx

I feel it my duty as a biologist who has worked with hyperthermophilic
organisms to correct you on multiple points.

Thx for the informed response. But you should be aware that Tom, to
whom you responded, is not a scientist and has no ambition to become a
scientist. He is an amateur with a fascination for the problem of the
origin of life. Like myself (though I like to tell myself that I know
a bit more about chemical thermodynamics than Tom.)

You are about 71C off on your upper temperature limit of. The limit
for reproducible life, that is, a bug that divides and grows is
currently at 121C (http://www.sciencemag.org/cgi/content/citation/
301/5635/934), and biologists continue to probe this upper limit,
believing it can be expanded. Allow me to reemphasize, life not only
grows at this temperature, it *thrives.* Some Thermotoga microbes are
impossible to keep in culture because they lyse when brought to
normal mesophilic temperatures.

There is also strong evidence, as shown between the free energy of
binding between alpha and beta subunits of tryptophan synthase in
Thermus thermophilus (http://www.jbc.org/cgi/content/abstract/
M210893200v1), that the enthalpy of salt bridges helps to drive
folding rather than the entropy of hydrophobic collapse. This would
explain the bias of salt bridges in thermophilic proteins. The
knowledge base in which you are stating your broad hypothesis also
appears to lack a thorough understanding of thermodynamics and protein
folding.

Interesting. Is there also a structural feature common to thermophilic
structural RNAs? I've heard that they are more GC rich in their stems,
but I've also seen this disputed.

It is also a general consensus amongst biologists that the last common
ancestor was most likely a thermophile, since it is so deeply rooted
in the tree of life. Read the following for more detail: [URL snipped]

It is a fairly widespread belief, but I wouldn't call it a consensus.
And hyperthermophily (or not) of the LCA really tells us little about
the conditions for the origin of life.

It is also a general consensus that life evolved from spontaneous
events of polymerization from early protein-metal precursors around
volcanic vents. I would google "composomes" to find out more on this
([snip big URL]).

Interesting. I had never heard of this hypothesis. At least not the
part about spontaneous polymerization. Are the ideas of the Segre group
considered 'consensus' now. Personally, I like the slogan of a
'lipid world', but I'm pretty skeptical regarding their specifics.
Especially their lingering commitment to a heterotrophic origin.

[Snip invective against Tom. No doubt he deserves this abuse, but the
more common practice here is to either ignore him or humor him.]



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