Posted on 05/29/2003 4:35:41 PM PDT by StupidQuestions
UV light may have sparked life on Earth
18:18 28 May 03
NewScientist.com news service
Ultra-violet light, long thought to be an impediment to the early formation of long organic molecules, may in fact hold the key to the origin of life, according to a new study.
Intense UV rays from a young Sun bombarded the early Earth and were thought likely to destroy any exposed organic molecules. But a new mathematical model implies the radiation actually helped select out the molecular seeds of life.
The earliest life on Earth is widely thought to have been based on RNA, the chemical cousin of DNA. RNA is made of subunits called nucleotides, which link together to form long polymer chains.
Certain components of RNA absorb UV light and act as "protectors", thereby giving it a survival advantage over other molecules, says Armen Mulkidjanian. Mulkidjanian, a biophysicist at Osnabrück University in Germany, led the team that developed the theoretical model.
"Simple RNA molecules can evolve under certain conditions - this is a well-developed field. But the question left is: how do you get the first long enough RNA polymer?" says Mulkidjanian. "Our model offers some physically plausible explanation of how long RNA polymers could emerge."
"This paper is important because it attacks that crucial problem," says Michael Yarus, an RNA world expert at the University of Colorado at Boulder. "If this problem could really be solved in a way that people agreed on, the RNA world would become a fact rather than a speculation."
Peculiar properties
Life on Earth is thought to have evolved about 3.7 billion years ago, when there was no protective ozone layer encasing the planet and UV radiation was 100 times more intense than today.
The nucleotides that make up RNA have three components - a sugar, a phosphate and nitrogen-containing base. "And these bases have very peculiar properties of being extremely efficient at quenching UV light," says Mulkidjanian, protecting the sugar and phosphate components which form the spine of the chain.
The team fed data on the photochemistry of various organic molecules into a computer model designed to simulate the effects of UV light on stability. "The effect was very pronounced in RNA," he says. In the presence of strong UV light, RNA was much more likely to form long chains than other molecules. -more-
(Excerpt) Read more at newscientist.com ...
Perhaps ironically, this is not an unreasonable or wildly irrational hypothesis. There is nothing in math and science that disallows this, and the more we know the more plausible it actually appears.
I have a several thousand year old account of witnesses that assert a great many things, including something about the universe, an elephant, and a whole lot of turtles.
Old does not mean "correct" (indeed, there is a general inverse correlation), nor does concensus determine truth (fallacies of reasoning, one and all). So I'm not sure why you mentioned what you did.
It isn't just your opinion; they are unrelated. A lot of the people here who argue in favor of abiogenesis and evolution are looking at it strictly from a simple physical/chemical standpoint, the same as if you were talking about weather phenomena. For science guys, talking about this stuff is like some people talk about cars. God is kind of orthogonal to the whole issue.
Does this mean that all the tomes that pre-date the Bible (and there are quite a few), many of which supposedly contain eye-witness accounts of a great many things, trump the Bible? That does seem to be what you are saying. In the big religious writing scheme of things, the Bible is a young whippersnapper upstart.
I am willing to in faith to accept the Bible as truth. Its teachings have not been disproven. While it is also true that D's theory has not been scientifically disproven either, I do not accept it as truth as there exists no corroborating evidence/testimony to prove it. I was pinged back here and answered the pinger's question to the best of my ability. Now I think I will go back outside let the thinkers continue without my distractions. Thank you for the interest and courtesy of allowing me to respond.
No I don't. I believe in and worship the One Triune God. Maker of all that is seen and unseen. Yourself and anyone else that may disagree with me have been given free will to believe in and worship whomever/whatever you wish. In America I am still free to pray for your souls.
This does sound like it could be big, if true. See here for the original paper. Here are the main points:
From the Background section: Aluminosilicate clays have been shown to catalyze the formation of oligonucleotides of up to 50 units long, when supplied by preformed and pre-activated mononucleotides under optimized laboratory conditions [14- 16]. However, no oligonucleotide formation from pentose phosphates and nitrogenous bases has been reported so far under the supposedly primordial conditions where the formation of amino acids, nitrogenous bases and carbohydrates took place. Furthermore, the current understanding implies that the environmental conditions on the primeval Earth were unfavorable for the survival of oligonucleotide-like polymers. A particularly important factor is that, due to the absence of the ozone layer, the UV flux at the Earth surface must have been approximately 100 times larger than it is now [17,18], causing deterioration of most organic molecules. The existing theories consider the high UV level as a major obstacle and offer several different strategies for hiding the first life forms from it (see e.g. ref. [10,19,20]). Here we invoke an alternative possibility, i.e. that the UV irradiation played a positive role in the origin of life by serving as a principal selective factor in the formation of pre-biological structures. Moreover, the influx of energy into the system in the form of the UV irradiation could be seen as the driving force required for the gradual complication of the system [1]. These considerations prompted us to analyze the possible effects of the UV irradiation on oligonucleotide formation in primordial conditions.
From the Results section: In general terms, UV irradiation of first RNA-like polymers could be damaging for their nitrogenous bases, their pentose-phosphate backbone and for the bonds between the bases and the backbone. It is known that the ether bonds in monomeric sugar phosphates are much more susceptible to UV damage than monomeric nitrogenous bases.... However, numerous studies of modern nucleic acids revealed an interesting paradox: nitrogenous bases, both purines and pyrimidines, of DNA and RNA are much more sensitive to the UV illumination than the pentose-phosphate backbone. It appears therefore that nitrogenous bases protect the pentose-phosphate backbone from the UV damage. Indeed, nitrogenous bases emit the absorbed UV energy extremely fast. ... This extremely efficient deactivation of the UV quanta by nitrogenous bases allows them to protect the compounds to which they are attached from UV-induced breakage. ... Further factors, which might contribute to the backbone protection, are the effective shielding of the backbone from the UV-light by nitrogenous bases, the excitonic coupling between the latter, and the elevated capacity of polymeric compounds to dissipate the excessive thermal energy without undergoing a mechanical damage.
(Skipping the detailed description of the experiment)
From the Discussion section: Thus, the results of our Monte-Carlo simulation indicate that a mechanism of natural selection, similar to the one that has driven the subsequent biological evolution, could have been responsible for the primordial polymerization. It seems quite unlikely that the extremely effective UV-quenching by all five major nucleobases is just incidental. Accordingly, one can assume that these bases had been selected to perform the UVprotecting function before they became involved in the maintenance and transfer of genetic information. This assumption provides a physically plausible rationale for the primordial enrichment in oligonucleotide-like compounds and also sheds new light on the earliest steps of evolution.
It is worth noting the following points:
- (i) In the UV-illuminated primordial world the probability of a UV-breakage was more than real for any compound. Correspondingly, those that succeeded to bind (trap) a UVquencher got a selective advantage. In the case of nitrogenous bases, the photogenerated radicals of the latter could even provide the energy needed to bind the UVprotector.
- (ii) The oligomerization, most probably inorganic template-guided (see ref. [10] for a comprehensive consideration of this point), further increased the degree of the UVprotection because then each UV-trap could protect several neighbouring backbone bonds. The minerals considered as potential primordial templates (see ref. [10] for their survey) are characterized by meshes of positively charged metal ions, so that a prospective oligomer unit required a negatively charged template-binding group (phosphate was the natural choice [10]) and a spacer region needed to fit into the lattice of positively charges at the template. The pentose groups are apt spacers as long as aluminosilicate clays indeed catalyse the formation of long oligonucleotides [14-16].
- (iii) In this “sugar-phosphate-centric” world the nitrogenous bases served just as protecting units, so that the UV-quenching capacity but not their exact chemical nature was important. Accordingly, these service units were replaceable and variable. Exactly this variability could have paved the way to the variability of the future genomes.
- (iv) In general, the increase in the fraction of double-stranded regions elevates the resistance of RNA backbone to UV-damage [25], as well as to hydrolysis [26]. Correspondingly, an occasional formation of double-stranded segments in primordial RNA-like polymers elevated, as it has been already discussed [26], the probability of their survival. Hence the survival, apparently, depended on the ability of chosen UVprotectors to form pairs.
- (v) Replication, most probably also initially template-guided [10], could have evolved as a process that just selected for more photostable biopolymers. Indeed, the first replication event, i.e. formation of a polynucleotide strand using another one as a template, could not be driven by the reproduction needs (the chicken and egg paradox). Replication could be, however, promoted by the simple fact that the UV-resistance of two interacting polynucleotide strands was higher than that of single strands.
The suggested mechanism turns the high UV levels on primordial Earth from a perceived obstacle to the origin of life (see e.g. ref. [19]) into the selective factor that, in fact, might drive the whole process. Indeed, biochemical condensation reactions proceed with release of water, so that the presence of latter favors hydrolysis of biological polymers. Because of this feature, Bernal [27] and many researchers after him (as reviewed in ref. [10]) advanced the view that life has begun in tidal regions, so that condensation of primordial monomers proceeded under “fluctuating” conditions where the wet periods, enabling the exchange of reagents, alternated with dry ones, favoring the condensation reactions. The awareness of the potential danger of the UV damage, however, prompted other scientists to invoke a UV-protecting water layer (see e.g. ref. [19]), which apparently would impede the condensation reactions. More recently, several authors even moved the point of the life origin to the bottom of the ocean, where the reducing power of minerals and/or of hydrothermal vents was considered to be the energy source for the first condensation events [28,29]. It remained unexplained, though, how inorganic reductants could drive primordial condensation reactions in water in the absence of enzymes (see the discussion in refs. [30,31].
In a sense, the absence of a consensus on a plausible mechanism for the origin and accumulation of the first RNA-like molecules has significantly hurt the development in the whole field and stimulated proliferation of the Panspermia hypothesis, not to mention various kinds of creationist ideas. It appears that our consideration of the UV irradiation as a positive, selective factor in primordial evolution may suggest a way out of the dead end. This view allows to place the cradle of life onto the sun-illuminated (semi)dry surface of the ancient Earth, as originally considered by Bernal [27]. Indeed, no other known energy source could compete with the UV component of the solar irradiation either in ability to serve simultaneously as both selective and driving force, or in continuity, strength, and access to the whole surface of Earth.
We believe that the ideas discussed above could eventually be tested experimentally. On one hand, nucleotides could be formed from simpler compounds under conditions of UVirradiation [7,8]. On the other hand, the ability of aluminosilicate clays to catalyze their polymerization was demonstrated [14-16]. Thus it seems very promising to try obtaining oligonucleotides from simpler compounds in a reactor system, which (i) uses UVirradiation as a selective force and an energy source and (ii) contains aluminosilicate clays as a polymerization template.
Here's a question for you experts: The paper mentions the "five major nucleobases" being nitrogenous. How many possible bases are there? And how many of them are nitrogenous?
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