Evolution and the second law of thermodynamics
RUMYM at BGEARN.ACAD.BG
Mon Mar 30 11:09:51 EST 1998
Ingvald Straume <ingvald at nordi.no> wrote:>>>>>>>>>
2) "Evolution contradicts the second law of thermodynamics."
Please, somone, help me! Give me some good scientiffic arguments that
will prove to the contrary these allegations . <<<<<<<<<<<<<<<<
I would reply to this question only as it has a "molecular" answer.
Unfortunately my argument is not against but rather in favour of the
allegation. The second law states that, under isothermal conditions, heat
cannot be converted into work by a system at equilibrium.
In biochemical terms, heat cannot be
converted into and stored as chemical energy, e.g. that of the
terminal-phosphate bonds of ATP. This is certainly not the case - the
chemiosmotic mechanism by which the transmembrane pH gradient produces ATP,
most probably operated first in equilibrium systems. Here is one such system:
A membrane (of some primordial vesicle) consists of two sectors - one
permeable to H+ only, and the other impermeable at all. It separates two
solutions at different pH. At equilibrium, H+ tends to diffuse down the
concentration gradient but is not allowed to go far from the membrane since
the counterion cannot pass and holds it close to the membrane. As a result,
a capacitor-like electric double-layer is formed at the permeable sector,
with the membrane sandwiched between the plates of the capacitor. This is
an almost classical physical picture - the transmembrane potential difference
is called Donnan potential.
What seems to be problematic is whether this potential difference is
preserved for points distant from the permeable sector - e.g. where the
ATP synthase is situated. If, at that place, there is no transmembrane
potential difference, a sudden opening of ion channels there would allow a
portion of H+ to cross the membrane and, accordingly, some ATP could be
synthesized. As the working system is initially at equilibrium, this ATP
synthesis would be a violation of the second law.
However many scientists would claim that, even for points distant from
the permeable sector, the potential difference is preserved. If so, opening
of H+ channels of the ATPsynthase would cause no transmembrane H+ flux since
the concentration difference would be neutralised by the potential difference.
So the crucial problem is whether or not the potential difference is preserved
for points distant from the permeable sector. The answer is negative, but
the explanation is electrochemical and perhaps not very suitable for discussion
on this forum.
According to this model, primordial vesicles for which there was pH difference
with the surroundings were able to produce osmotic work and obtain chemical
energy by incidental openings of H+ channels at spots generally impermeable.
Of course, the yield was too low and the whole cycle too slow, so further
improvement consisted in capturing and using external energy to accelerate a
segment of the cycle - e.g. transport of H+ out of the vesicle. The point
is that external energy can only be superimposed on some preexisting
mechanisms - otherwise it could only be destructive.
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