Re: Planet Densities (actually not, but who cares anyway)

Eugene Leitl (
Thu, 14 Nov 1996 17:07:12 +0100 (MET)

On Wed, 13 Nov 1996, James Rogers wrote:

> At 10:32 PM 11/12/96 -0500, you wrote:
> >James Rogers wrote:
> >> Ice isn't conducive to life and
> >> very hot water/steam is extremely destructive to organic compounds.
> >>
> >
> >Actually, this is not true. Organic compounds used to living at our
> >pressure and temp are very sensitive, but only because of the elements
> >their proteins use to bind themselves together with. A protein molecule


> >is like a messed up ball of yarn, with energy bonds wherever the strands
> >cross. TO do its work as a protein, it must have a certain amount of

So you are refering to the folded state of the protein, vs. molten

> >springiness to it to stay in solution, and must be able to be broken
> >apart with little energy input. Too much energy input, and the molecule
> >will break apart and precipitate out of solution, which is how egg

Well, it is not "breaking", it is a simple, sharp phase transition from
the precisely defined point in state (=conformation space, form follows
function (aka mapping (folding) of a linear polymer (string), a
precisely defined, intricate 3-shape, which maps to the task space of
that particular protein in a wet context)) to a wide variety (a very
large region of energetically accessible state space) of denaturated
structures. This phase transition is large-scale property, where lots of
uniquely arranged amino acids in a protein chain "don't show their face".
(A somewhat contraintuitive insight, since usually we're not expecting
such simple behaviour from an archetypally complex system ;)

It might be irreversible, it might not. Proteins are molecular machines,
their folding pathways and kinetics have been careful optimized by the
Darwinian evolution generator process. Even so, the stuff sometime
misfolds, and has either be marked for destruction, or carefully massaged
(annealed) by the chaperonine chaps, i.e. hsps.

Predicting the tertiary structure of a protein from its primary structure
(sequence string) is _the_ Holy Grail of computational biology. Protein
engineering, de novo design and thus soft nanotech are the next logical
steps, then.

> >whites get white when you boil them. Using different elements at the
> >energy bond points than is used for normal temp organisms allows for
> >much higher temperature tolerance, as the bonds are much tighter, and

I can assure you, extreme thermophiles bugs use exactly the same amino
acids as the rest of us, just in a different sequence. A single point
mutation can increase the stability of a protein dramatically.

> >require higher energy input to break them apart, however this makes for
> >a very tightly bound molecule that only does its chemical work at a
> >higher temperature. For example, a common protein in bacteria which uses
> >iron in its makeup, has a corollary protein in hyperthermophilic
> >bacteria (bacteria that can live above boiling) that uses tungsten
> >instead.

Ok, so you're refering to the cofactors. But this is fringe adaptation,
the rest of the beastie is still conventional. (You're not referring ;)
to Cytochrome C, do you? Do they actually use tungsten instead of iron?)

> >These bacteria have been recovered from deep sea volcanic vents, deep
> >oil wells, and deep geothermal systems, and have exhibitied preference
> >for temperatures above 180 degrees F (about 90 C) up to as much as 275 F
> >(about 130 C). As more varieties are recovered, the upper limit seems to
> >creep higher, especially as specimens are recovered from deeper and
> >deeper sites.
> >
> True, there are some organisms who can thrive in this environment, but their
> makeup is significantly different than surface dwelling organisms. The

Molecular structure or plain morphology? They're archae, they're sure
simple bugs. Can you specify what you mean by makeup?

> pressure where they live allows liquid water reactions to continue to occur.
> Even then, there is a soft limit somewhere around 150-170 C for most
> organics. The absolute hard limit on any planet is somewhere around 375 C

Certainly for proteins, for aquathermal water is a fierce solute. There
are lots of organic compounds which can survive hefty temperatures,
however. NASA uses polymers capable of withstanding 1500 deg C for short
periods, noticeably lower temps for indefinite time.

> since this is where water goes supercritical, although very few organics

Uh oh, this is a seriously bad customer. Whether sand or gold, it
dissolves about anything. Many minerals are of geohydrothermal origin.
Quartz crystals (which are used for computer and clock xtals) are grown
in autoclaves by a hydrothermal process (specifically: a transport
reaction in a temperature gradient).

> would survive even to this point (except maybe some halides and a few
> proteins). Cells require a pretty broad spectrum of organic compounds to

I beg to differ, only the biopolymer stuff. I doubt steroids will notice
much of it. Just remember the hopanes in microfossils.

> operate, and the number of options decreases rapidly as the temperature
> increases.
> Sub-zero lifeforms are not that unusual, although it is unusual for higher
> lifeforms to exist in these environments. In an environment that is

Arctic fishes can exist in contiguous (slightly) subzero habitats.
They've developed a paraphernalia of methods to cope with this harsh
environments, particularly advanced cryprotectives, basically
poisoning ice nucleation. They are also using lots of slime in sensitive
(gill) areas to prevent ice microcrystals from crossing over into the

For more, have a look at:

> perpetually subzero, I would expect to find either very primitive nervous
> systems, or nervous systems that operated in a different fashion than ours.

Well, they don't use saltatory spike propagation, but everything else is
canonical. Ok, their lipide bilayer composition is significantly more
fluid, to prevent phase transitions to a 2d crystal, which is not
exactly something desirable. Membrane fluidity is dynamically adjusted,
by expression of the right genes at the right time in the right

> The nervous systems found on this planet don't operate well in cold
> environments, since they rely on ion/molecule transport. This is why
> mammals found in cold climates on this planet require immense quantities of
> insulation.

It ain't only the CNS, the entire metabolism requires a precisely defined
point in parameter space. Each reaction shows different response to
change in parameters, so if you're too much off-key, you're dead. (A
toast of deuterium oxide to that).


> -James Rogers

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