Re: Exotic life-sustaining bio-energy-conversion mechanisms
From: William Morse (wdmorse_at_twcny.rr.com)
Date: 02/27/05
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Date: Sun, 27 Feb 2005 01:04:40 -0500 (EST)
"Gil Lawton" <gillawton@earthlink.net> wrote in news:cvqjih$2tuu$1
@darwin.ediacara.org:
(snip)
> Also, I am curious as to whether, and if so how, exotic opportunistic
> biological energy conversions might divided up the labors of such
> conversions between respiratory, on the one hand, and metabolic
> processes, on the other. Do distinctions between respiration and
> metabolism tend to disappear at diminishing microscopic levels,
> or do they persist in some sense, even there?
Respiratory functions in general have to do with producing energy, while
metabolic functions have to do with producing structure. On a cellular
machinery basis they share some features, but the distinctions remain at
all but the most fundamental levels. But if you really are interested in
this, you will be leaving the realm of evolution and entering that of
biochemistry.
> My reading on these issues has been casual up to now; but I am
> becoming interested in any more advanced information, if it
> can be accessed by me.
> Casual reading has led me to a vague understanding that heat
> energy is utilized directly where it is available, that sulphur is
> respirated by some organisms around deep sea thermal vents,
> that some organisms metabolize or respirate methane or other
> hydrocarbon compounds in some way... and, even, that
> organisms found inside rocks convert energy to life sustenance
> so slowly, and propagate so gradually, that "life" as, say, humans
> engage in it in fractions of seconds is measured out for them in
> centuries, or eons.
You need to understand that life on earth is built around high-energy
phosphate bonds. Any energy source that cannot drive the formation of a
phosphate bond (and heat energy in general cannot) will not be utilized
directly. Respiration requires an electron donor and an electron
receptor, with enough delta G (difference in energy) to create a
phosphate bond. The rate at which the reaction occurs is a different
question - and as you note the interesting thing about the microbes in
rocks is that they can maintain a minimum metabolism (keep their
structure intact) with extraordinarily low rates of respiration.
> I would guess that whatever studies may have been done in
> reference to examining life-sustaining-energy-conversion
> mechanisms have been, and are, of particular interest to those who
> design sample-taking and sample-preservation in pursuit of
> learning whether life, however exotic to us, may persist on foreign
> planets in our solar system.
If life on foreign planets uses some other main energy source than
phosphate bonds, then much of what we know about respiration on earth is
probably useless for extraterrestrial biology.
Yours,
Bill Morse
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