From: Mike Lorrey (mlorrey@datamann.com)
Date: Sun Jan 27 2002 - 19:53:38 MST
Doug Jones wrote:
>
> Mike Lorrey wrote:
> >
> > Not really, Doug. The question to ask is WHY chlorophyll replaced
> > rhodopsin. The reason is that the early terran atmosphere density was 52
> > atmospheres, mostly made up of CO2. Thus, the type of light that early
> > life forms experienced was distinctly different from that of today.
> > Definitely much redder, ergo rhodopsin was a more efficient chemical for
> > transforming sunlight into chemical energy than chlorophyll, given that
> > spectral band. As the CO2 density in the atmosphere decreased as CO2 was
> > sequestered into limestone by those life forms, the spectrum that life
> > forms saw chaged to a much more yellow/blue dominated spectrum,
> > whereupon chlorophyll became the more efficient chemical.
> >
> > Chemistry and the laws of physics to not change from planet to planet,
> > so to expect that the most effective and efficient and easiest chemical
> > pathways to NOT be used in any environment given similar circumstances
> > is specious thinking in the extreme.
>
> I believe you're mistaken, Mike. Rhodopsin's absorbance peak is 496 nm,
> quite close to sunlight's peak radiation at 555 nm. Rhodopsin chemistry
> is centered on the sweet spot, while chlorophyl (which came later),
> *reflects* the majority of sunlight energy! Green algae originally were
> bottom dwellers, subsisting on the purplish light that filtered through
> the then-dominant rhodopsin forms- no accident that chlorophyl absorbs
> everything that rhodopsin does not.
>
> Chemistry and physics are the same, history need not repeat itself.
Yes, but this doesn't disprove my point. Is x amount of rhodopsin more
efficient at generating y amount of ATP than the same amount of
chlorophyll or not, and how does this relate to the energy cost of
producing rhodopsin and chlorophyll? Chlorophyll wouldn't have become
dominant if it were not, from an evolutionary standpoint, more
effective.
Furthermore, the peak absorption of each is really irrelevant. It is the
total absorption across all bands that matters, AND the band pattern of
sunlight at the earth's surface, not in space.
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