An efficient prebiotic synthesis of cytosine and uracil
Keywords Prebiotic evolution . Self replicating-catalyzing systems. Equilibrium. Inhomogeniety
Introduction Some facts about the origin of life are well understood, others are still the subject of current research. The first living things on earth were the single celled prokaryotes, which appeared just a few hundred million years after the formation of the Earth. Many theories emerged in the early nineteenth century to explain the mysterious origin of life on earth and in so doing, serialize the events that led to it.Haldane and Oparin: The Primordial Soup TheoryNo new notable research or theory on the subject of life and its origin appeared until 1924, when Oparin suggested that a primeval soup of organic molecules might have been created in the presence of external factors such as the sunlight and the atmosphere. Later, the molecules in this broth might have combined in an ever-more complex manner to form special composites called the Coacervate droplets. These globules would have then expanded by fusing with other drops, and replicated via fission into daughter droplets. Simultaneously, J.B.S Haldane came up with his theory, according to which, the earth had prebiotic oceans, unlike their present day equivalents, which were the reservoirs for the generation of building blocks of life. Many theories that followed were more or less based on the Haldane-Oparin theory.The Enigma of life:A. The Equilibrium Hypothesis.Many theories that have evolved to explicate the origin of life, and most of them come up with a distinct concept to enlighten either a particular event during the origin of life or reconstructing the entire process in totality. Nonetheless, an appropriate cause for the origin remains unexplained; why did life originate in the first instance? And was it predetermined or just an accidental phenomenon? The following section will make an effort to answer this with the idea called, Equilibrium. Equilibrium or stability is a term that has its significance, from the
atomic level to the macro, in our universe. The ultimate aim of any process (reaction, sequence or phenomena) is nothing but attainment of stability, something which in turn accounts for its (process) subsistence. If we look at the earth and its past we see that it underwent many progressive transformations, some of which have been summarized below:From a cloud of fiery swirling gases to a cooled liquid, the reason for this change being that molecules at the gaseous phase are more in number and disordered, more in partial pressure and volume, hence the equilibrium is shifted in a direction that reduces randomness, number of molecules and volume (volume of vapour > volume of water) i.e. to a liquid state. During the cooling, lighter constituents were raised up which latter formed the hard rocky crust thereby encircling a hot turbulent liquid at the nucleus, solidification further decreased the internal temperature, pressure and randomness, which accounted for the added stabilization of the earth's state. The seething liquid beneath searched out weak spots in the crust and poured out as molten lava, this helped in harmonizing the internal temperature with the surrounding and the crust. Simultaneous hardening added an extra undermining weight to the outside, causing the crust to sink but this was poised by folding surfaces elsewhere into mountains, valleys etc. consequently achieving an equilibrium again. After few years of its cooling, there occurred a transformation from a reducing atmosphere to an oxidizing one, but what was the need when we had chemoheterotrophs thriving in an anaerobic milieu and were utilizing organic compounds from the "primordial soup"? Well what appears to be the answer is that early chemoheterotrophs metabolized organic-comp. to CO2, as a result the concentration of this gas increased thereby decreasing the amount of stored organic compounds mainly hydrocarbons, this unsteadiness was accompanied with continuous exposure of sun's light energy on the dark earth, because of heavy raining, which caused the thinning of the clouds in the atmosphere, thus the extra addition of light energy also had to be counterbalanced. The evolutionary event, leading to the synthesis of pigments that could absorb sun's light along with the utilization of the superfluous CO2 to give O2 as a metabolic waste, was called photosynthesis.
Further the unevenness due to few photosynthesizing organisms amid many chemoheterotrophs was defused when O2, a poison to the anaerobes at that time, bent an evolutionary pressure (Oxygen-Holocaust) instigating some microbial lineages to give aerobic generations and this was one of the prime turning points. B. The Inhomogeneity Hypothesis - a clue to the exobiotic life, if existent.Inhomogeneity, 10-43seconds after the ‘Big Bang' would have clumped matter much earlier than that led to the fruition of earth 4.5 billion years ago. Evolution probably started much before we learned.10-43seconds after the Big Bang, refers to the time when the universe was being formed. Now during this rapid inflation of the universe, all the matter spurt far apart, that too very uniformly according to the ‘Big-Bang' theory, this theory nevertheless fails to explain the non uniformity observed in the universe on smaller scales i.e. clumping of galaxies, clusters of galaxies and super clusters of clusters. It has been recently brought to light those during10-43 seconds after the ‘Big Bang', incipient clumps of matter started developing due to gravitational self-attraction. So an alternate presumption that can be made is the likelihood of any one of these untimely clumping that would have started evolving with a similar set of phases that our planet underwent during its maturity and may well be harboring life much before the seeds of first beings were sown here. ConclusionHence to sum up, it was not a conscious premeditated endeavor by nature to make this parched lifeless planet, before 4.5 billion years ago, as viable as it appears now or to have sown the seeds of life thereafter, a particular environmental change demanded a reconstruction to stabilize, until a perfect equilibrium was achieved, and life being the end result, or one may say, Life evolved.
References1. Wilde SA, Valley JW, Peck WH, Graham CM. Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago. Nature 409 (6817):175-8, 2001.2. Archer, Corey; Vance, Derek. Coupled Fe and S isotope evidence for Archean microbial Fe(III) and sulfate reduction. Geology 34 (3):153-156, 2006.3. Cavalier-Smith, Thomas; Brasier, Martin;Embley, T. Martin. Introduction: how and when did microbes change the world?. Phil. Trans. R. Soc. B 361 (1470): 845-850, 2006.4. Summons, Roger E.; et al. . "Steroids, triterpenoids and molecular oxygen". Phil. Trans. R. Soc.B 361 (1470):95-168, 2006.
5. Balme DM. Development of Biology in Aristotle and Theophrastus: Theory of Spontaneous Generation. Phronesis.7 (1-2): 91-104. Dobell C. New York (EUA);1960.6. Oparin AI. Origin of Life. Dover Publications, New York; 1953. 7. Oparin, A I. The Origin of Life. Dover Publications .New York; 1952.
8. Bryson B. A Short History of Nearly Everything. pp. 300-302; 2003.9. Morse JW, MacKenzie FT. Hadean Ocean Carbonate chemistry. Aquatic Geochemistry. 4:301-319, 1998. 10. Sleep NH et al. Annihilation of ecosystems by large asteroid impacts on earlyEarth. Nature. 342: 139-142,1989. 11. Maher, Kevin A.; Stephenson DJ. Impactfrustration of the origin of life. Nature. 331 (6157):612-614,1988. 12. Orgel, Leslie E. Prebiotic adenine revisited: Eutectics and photochemistry. Origins of Life and Evolution of Biospheres 34: 361-369, 2004.13. Robertson MP, Miller SL. An efficient prebiotic synthesis of cytosine and uracil. Nature. 375 (6534):772-774,1995.14. Bada JL, Bigham C, Miller SL. Impact Melting of Frozen Oceans on the Early Earth:Implications for the Origin of Life. PNAS .91 (4):1248-1250, 1994.15. MojzisSJ et al. Evidence for life on earth before 3,800 million years ago. Nature. 384 (6604):55-59,1996. 16. LazcanoA, Miller SL. How long did it take for life to begin and evolve tocyanobacteria? Journal of Molecular Evolution. 39: 546-554,
1994.17. Miller SL. Production of Amino Acids Under Possible Prim itive Earth conditions. Science. 117:528-529, 1953.
An efficient prebiotic synthesis of cytosine and uracil - …
An efficient prebiotic synthesis of cytosine and uracil.
AB - Numerous problems exist with the current thinking of RNA as the first genetic material. No plausible prebiotic processes have yet been demonstrated to produce the nucleosides or nucleotides or for efficient two-way nonenzymatic replication. Peptide nucleic acid (PNA) is a promising precursor to RNA, consisting of N-(2-aminoethyl)glycine (AEG) and the adenine, uracil, guanine, and cytosine-N-acetic acids. However, PNA has not yet been demonstrated to be prebiotic. We show here that AEG is produced directly in electric discharge reactions from CH4, N2, NH3, and H2O. Electric discharges also produce ethylenediamine, as do NH4CN polymerizations. AEG is produced from the robust Strecker synthesis with ethylenediamine. The NH4CN polymerization in the presence of glycine leads to the adenine and guanine- N9-acetic acids, and the cytosine and uracil-N1-acetic acids are produced in high yield from the reaction of cyanoacetaldehyde with hydantoic acid, rather than urea. Preliminary experiments suggest that AEG may polymerize rapidly at 100°C to give the polypeptide backbone of PNA. The ease of synthesis of the components of PNA and possibility of polymerization of AEG reinforce the possibility that PNA may have been the first genetic material.
An efficient prebiotic synthesis of cytosine?
The efficient prebiotic synthesis of cytosine from urea and cyanoacetaldehyde (CA) has recently been claimed to be invalid on the basis of possible side reactions of the starting materials and the inapplicability of prebiotic syntheses using drying beach conditions. We therefore have investigated the synthesis of cytosine and uracil from urea and cyanoacetaldehyde at 100 °C under dry-down conditions, and in solution at 4 °C and -20 °C. We find that cytosine is produced from the low temperature experiments more efficiently than calculated from the Arrhenius extrapolation from higher temperatures, i.e., 60-120 °C. In addition, we find that CA dimer is as efficient as the monomer in cytosine synthesis. We also studied whether evaporating very dilute solutions of nonvolatile organic compounds will concentrate according to theory. Solutions as dilute as 10-4 M concentrate from pure water approximately according to theory. Similar solutions in 0.5 M NaCl have less than theoretical concentrations due to absorption, but concentrations near dryness were very high.