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Natural Science Forum / Physics / Research / October 2007Could human skin be photosynthetic?
I've always thought that, were it possible for biology to harness ionizing radiation for energy, some organism would already have done so. The ground contains vast fungal and bacterial communities, but also contains "light sources" in the form of uranium ore deposits. Well, it looks like my suspicions were correct: Inside the Chernobyl reactor: fungus feeds on radiation http://www.wtnrradio.com/news/story.php?story=262 But there's more... Apparently the fungus uses an unsuspected photosynthetic molecule: melanin. It's not green like light-loving plants, instead it's brown and eats gamma rays. What other organism deals with hard radiation and employs the melanin molecule? People? Expose caucasian skin to ionizing radiation (hard UV sunlight) and it ramps up melanin production. Melanin absorbs UV and acts as a shield. "Getting a sun tan." Or be of non-European ancestry and you're already shielded. But wait a minute. What if human skin was bright green. Would you think to yourself "ah, our skin contains a dye molecule which shields against visible light?" Or instead would you think "ah, skin contains an energy-harvesting molecule which uses visible light to synthesize it's own fuel?" In other words... if I have a dark tan, and I go sit in summer sunlight without eating, will avoid starvation longer than if I stayed indoors without eating? Maybe vitamin-D isn't the only thing made by human skin in sunlight. Another question: does human melanin production respond to ALL ionizing radiation? If I stick my hand under a high-power gamma ray source for a few minutes per day, will I receive a nice dark tan? (I'd be sure to start slowly so I don't get a bone-deep sunburn at the start.) And just how effective is melanin as a shielding material for high energy photons? (When compared to equal mass of, say, metallic lead?) ((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer beaty a chem washington edu UW Chem Dept, Bagley Hall RM74 billb a eskimo com Box 351700, Seattle, WA 98195-1700 ph425-222-5066 http://staff.washington.edu/wbeaty/ [ Mod. Note: Please restrict further comments to relevant physics. -ik ] > I've always thought that, were it possible for biology to harness > ionizing radiation for energy, some organism would already have done [quoted text clipped - 12 lines] > What other organism deals with hard radiation and employs the melanin > molecule? People? [snip] The cited article is sensationalist not technical. How will you couple incoming energy to biochemistry, specifically production of sugar or ATP? Chloroplasts are the best organelles from evolution, and they are limited in sugar fixation by RuBisCO. RuBisCO is possibly the worst enzyme on Earth - the slowest (~3 turnovers/sec) and least efficient (~1%; poisoned by oxygen). 30% of the soluble protein in leaves is RuBisCO. Optical membrane ion pumps giving direct charge separation are no improvement (e.g., purple bacteria). The "Green Revolution" is crap. 50 years of Mendelian breeding could be replaced by a year in MIT or Caltech gene-gineering labs. Site-specific mutagenesis of RuBisCO to raise its loathsome performance to still pitiful 50 turnovers/second and 10% efficency would increase farm productivity 16,600%. Now put *those* chloroplasts into soldiers and watch them lay naked in the sun feeding themselves. (The "Green Revolution" is crap anyway. 1970s' 0.1 wt-% mixed THC isomer marijuana was classically bred by stoners to 30 wt-% /_\-9 THC single isomer by the 1990s - Northern Lights 100% cloned female hydroponic boo. Where was the corresponding progress in corn, wheat, and rice by batallions of PhDs with high eight-figure annual budgets worlwide?)  SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 > [ Mod. Note: Please restrict further comments to relevant physics. -ik ] > [quoted text clipped - 17 lines] > > The cited article is sensationalist not technical. The original is available for comment at PLoS-One: <http://www.plosone.org/article/fetchArticle.action?articleURI=info:doi/10.1371/j ournal.pone.0000457> or <http://tinyurl.com/yp73eg> for the word-wrap happy news clients. > How will you couple incoming energy to biochemistry, specifically > production of sugar or ATP? >From their abstract: --------- Methodology/Principal Findings Ionizing irradiation changed the electron spin resonance (ESR) signal of melanin, consistent with changes in electronic structure. Irradiated melanin manifested a 4-fold increase in its capacity to reduce NADH relative to non-irradiated melanin. -----end snippet---------- I would quibble that NADH _is_ the reduced form of NAD. I assume they meant that the capacity to reduce NAD was enhanced. If you can reduce NAD, you can make sugar. SignatureDavid Winsemius David Winsemius wrote: > Uncle Al <UncleAl0@hate.spam.net> wrote in news:47067C65.28499B03@hate.spam.net: > [quoted text clipped - 44 lines] > meant that the capacity to reduce NAD was enhanced. If you can reduce > NAD, you can make sugar. Cut through the grantology, 1) What is the native capacity of melanin to reduce NAD that is now 4X increased? "the capacity to reduce NAD was enhanced" Didn't say it worked, or at what efficiency, or if more than one cycle was possible. 2) How much radiation need one absorb to *net* 2000 Cal/day metabolism? A rad is 100 ergs/gram. Human LD50 is ~500 rads or 50,000 ergs/gram deposited. 50,000 ergs is 1.2x10^(-6) Calories. 100 ergs = 2.39x10^(-9) food Calories. 2000 food Calories = 8.4x10^(11) ergs. Divide that by the overall conversion efficency for incident daily irradiation. Easier to eat a Twinkie. 3) Tell us how to power a photosynthetic animal without frying it outright at any frequency, microwave to visible to Co-60 gamma. SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 > David Winsemius wrote: >> [quoted text clipped - 3 lines] >> > [ Mod. Note: Please restrict further comments to relevant physics. >> > -ik ] snipped Bill's original >> > The cited article is sensationalist not technical. >> [quoted text clipped - 20 lines] >> meant that the capacity to reduce NAD was enhanced. If you can reduce >> NAD, you can make sugar. > 1) What is the native capacity of melanin to reduce NAD that is now > 4X increased? "the capacity to reduce NAD was enhanced" Didn't say > it worked, or at what efficiency, or if more than one cycle was > possible. Appears they showed only that irradiated melanin could act as catalytic enhancer of a coupled reaction between NADH (the energy source) and ferricyanide. Since they didn't reduce NAD with the irradiated melanin, I take back what I said about potential coupling to gluconeogenesis. > 3) Tell us how to power a photosynthetic animal without frying it > outright at any frequency, microwave to visible to Co-60 gamma. Talk to Bill. He is the science fiction writer. Put aside absorptive efficiency for the moment. I suspect that even the 661.65 keV gamma rays that did interact with melanin would not be absorbed, only scattered, and secondary radiation scatter would be almost as harmful to a complex organism as the incident radation. SignatureDavid Winsemius > 3) Tell us how to power a photosynthetic animal without frying it > outright at any frequency, microwave to visible to Co-60 gamma. It was stated elsewhere in the thread that the solar intensity is 1000 watts per square meter. I'm pretty sure that's only 100 watts per square meter. The mere fact that plants aren't mobile and (unlike Ents) don't walk should have settled the issue, even before getting to the detailed Physics. If there is a way, nature would have found it by now. In article <1191968604.918399.82150@50g2000hsm.googlegroups.com>, Rock Brentwood <markwh04@yahoo.com> writes: > It was stated elsewhere in the thread that the solar intensity is 1000 > watts per square meter. I'm pretty sure that's only 100 watts per > square meter. Wrong. 1.37 kW / m² is a standard value. This is above the atmosphere; below the atmosphere, it's about a kW per square meter. (Of course, the "solar constant" is not really constant, even above the atmosphere, due to the slight variability of the sun, but this is a small effect.) Two points: First, these days it is easy to check such values on the internet in a matter of seconds with a search engine. (Of course, not everything on the internet is true, but I don't detect a conspiracy to populate the internet with bogus values for the solar constant.) Second, think about it. Imagine yourself in a dark room with a 100-Watt light bulb positioned so that it illuminates a square meter. How does it feel? Now, go outside on a sunny day. It probably feels warmer. Or do the comparison with a solar-cell powered calculator or something and see which produces more current. > > 3) Tell us how to power a photosynthetic animal without frying it > > outright at any frequency, microwave to visible to Co-60 gamma. > It was stated elsewhere in the thread that the solar intensity is 1000 > watts per square meter. I'm pretty sure that's only 100 watts per > square meter. Physics Today March 2007 p37 "Solar energy conversion" states that the sun delivers a power of P = 1.2x10^5 TW to the earth; the radius of the earth is r = 6.37 Mm; so the area of the earth's disk is A = pi r^2 = 1.3x10^14 m^2. This gives an average intensity of P/A = 940 W/m^2. Signature---------------------------------+--------------------------------- Dr. Paul Kinsler Blackett Laboratory (QOLS) (ph) +44-20-759-47520 (fax) 47714 Imperial College London, Dr.Paul.Kinsler@physics.org SW7 2BW, United Kingdom. http://www.qols.ph.ic.ac.uk/~kinsle/ > 3) Tell us how to power a photosynthetic animal without frying it > outright at any frequency, microwave to visible to Co-60 gamma. Straw man. Why not also tell us how to create a complete eye from one mutation? My point being that to receive some incremental benefit, there's no need to power the entire animal (e.g. vitamin-D production exists, even though it doesn't power an entire animal.) If death by starvation is common among mammals, then those which receive even a fairly small energy gain via sunlight, might squeak by while their non-photosynthesizing competitors are selected out. Of course the benefit could be so insignificant that it would be too far down in the noise, and wouldn't be "noticed" and amplified by evolution. And why are all of us not already like Euglenas: both motile and green-skinned? On Oct 9, 8:16 pm, Rock Brentwood <markw...@yahoo.com> wrote: > It was stated elsewhere in the thread that the solar intensity is 1000 > watts per square meter. I'm pretty sure that's only 100 watts per > square meter. Nope, search on "solar constant. > If there is a way, nature would have found it by now. That's what *I* said. The melanin discovery looks interesting, and gives me an excuse for wild speculation about any other common melanin-using organisms. :) ((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer beaty a chem washington edu UW Chem Dept, Bagley Hall RM74 billb a eskimo com Box 351700, Seattle, WA 98195-1700 ph425-222-5066 http://staff.washington.edu/wbeaty/ |
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