vano_t
| QUOTE | | რეპლიკაციის მოდელი რა შუაშია? კითხვას რომ ვერ იგებ, უნდა დაანებო იქ კამათს თავი |
მე ვერ ვიგებ? როგორ არის წარმოსადგენიო და ა ბატონო:
| QUOTE | Current models
There is no truly "standard model" of the origin of life. Most currently accepted models draw at least some elements from the framework layed out by the Oparin-Haldane hypothesis. Under that umbrella, however, are a wide array of disparate discoveries and conjectures such as the following, listed in a rough order of postulated emergence:
1. Some theorists suggest that the atmosphere of the early Earth may have been chemically reducing in nature, composed primary of Methane (CH4), Ammonia (NH3), Water (H2O), Hydrogen sulfide (H2S), Carbon dioxide (CO2) or carbon monoxide (CO), and Phosphate (PO43-), with molecular oxygen (O2) and ozone (O3) either rare or absent.
2. In such a reducing atmosphere, electrical activity can catalyze the creation of certain basic small molecules (monomers) of life, such as amino acids. This was demonstrated in the Miller-Urey experiment by Stanley L. Miller and Harold C. Urey in 1953.
3. Phospholipids (of an appropriate length) can spontaneously form lipid bilayers, a basic component of the cell membrane.
4. A fundamental question is about the nature of the first self-replicating molecule. Since replication is accomplished in modern cells through the cooperative action of protiens and nucleic acids, the major schools of thought about how the process originated can be broadly classified as "proteins first" and "nucleic acids first".
5. The principal thrust of the "nucleic acids first" argument is as follows:
1. The polymerization of nucleotides into random RNA molecules might have resulted in self-replicating ribozymes (RNA world hypothesis)
2. Selection pressures for catalytic efficiency and diversity might have resulted in ribozymes which catalyse peptidyl transfer (hence formation of small proteins), since oligopeptides complex with RNA to form better catalysts. The first ribosome might have been created by such a process, resulting in more prevаlent protein synthesis.
3. Synthesized proteins might then outcompete ribozymes in catalytic ability, and therefore become the dominant biopolymer, relegating nucleic acids to their modern use, predominantly as a carrier of genomic information.
As of 2008, no one has yet synthesized a "protocell" using basic components which would have the necessary properties of life (the so-called "bottom-up-approach"). Without such a proof-of-principle, explanations have tended to be short on specifics. However, some researchers are working in this field, notably Steen Rasmussen at Los Alamos National Laboratory and Jack Szostak at Harvard University. Others have argued that a "top-down approach" is more feasible. One such approach, attempted by Craig Venter and others at The Institute for Genomic Research, involves engineering existing prokaryotic cells with progressively fewer genes, attempting to discern at which point the most minimal requirements for life were reached. The biologist John Desmond Bernal, coined the term Biopoesis for this process, and suggested that there were a number of clearly defined "stages" that could be recognised in explaining the origin of life.
* Stage 1: The origin of biological monomers
* Stage 2: The origin of biological polymers
* Stage 3: The evolution from molecules to cell
Bernal suggested that evolution may have commenced early, some time between Stage 1 and 2.
Origin of organic molecules
There are two possible sources of organic molecules on the early Earth:
1. Terrestrial origins - organic synthesis driven by impact shocks or by other energy sources (such as ultraviolet light or electrical discharges) (eg.Miller's experiments)
2. Extraterrestrial origins - delivery by objects (eg carbonaceous chondrites) or gravitational attraction of organic molecules or primitive life-forms from space
Recently estimates of these sources suggest that the heavy bombardment before 3.5 Gyr ago within the early atmosphere made available quantities of organics comparable to those produced by other energy sources.[25]
"Soup" theory today: Miller's experiment and subsequent work
Biochemist Robert Shapiro has summarized the "Primordial Soup" theory of Oparin and Haldane in its "mature form" as follows[26]:
1. The early Earth had a chemically reducing atmosphere, as discussed above.
2. This atmosphere, exposed to energy in various forms, produced simple organic compounds ("monomers").
3. These compounds accumulated in a "soup".
4. By further transformation, more complex organic polymers— and ultimately life— developed in the soup.
Regarding the reducing atmosphere
Whether the mixture of gases used in the Miller-Urey experiment truly reflects the atmospheric content of early Earth is a controversial topic. Other less reducing gases produce a lower yield and variety. It was once thought that appreciable amounts of molecular oxygen were present in the prebiotic atmosphere, which would have essentially prevented the formation of organic molecules; however, the current scientific consensus is that such was not the case. (See Oxygen Catastrophe).
Regarding monomer formation
Main article: Miller experiment
One of the most important pieces of experimental support for the "soup" theory came in 1953. A graduate student, Stanley Miller, and his professor, Harold Urey, performed an experiment that demonstrated how organic molecules could have spontaneously formed from inorganic precursors, under conditions like those posited by the Oparin-Haldane Hypothesis. The now-famous "Miller-Urey experiment" used a highly reduced mixture of gases – methane, ammonia and hydrogen – to form basic organic monomers, such as amino acids.[27] This provided direct experimental support for the second point of the "soup" theory as described above, and it is around the remaining three points of the theory that much of the debate now centers.
Apart from the Miller-Urey experiment, described above, the next most important step in research on prebiotic organic synthesis was the demonstration by John Oró that the nucleic acid purine base, adenine, was formed by heating aqueous ammonium cyanide solutions.[28]
Regarding monomer accumulation
The "soup" theory relies on the assumption proposed by Darwin (see above) that in an environment with no pre-existing life, organic molecules may have accumulated and provided an environment for chemical evolution.
Regarding further transformation
The spontaneous formation of complex polymers from abiotically generated monomers under the conditions posited by the "soup" theory is not at all a straightforward process. Besides the necessary basic organic monomers, compounds that would have prohibited the formation of polymers were formed in high concentration during the Miller-Urey and Oró experiments. The Miller experiment, for example, produces many substances that would undergo cross-reactions with the amino acids or terminate the peptide chain.
More fundamentally, it can be argued that the most crucial challenge unanswered by this theory is how the relatively simple organic building blocks polymerise and form more complex structures, interacting in consistent ways to form a protocell. For example, in an aqueous environment hydrolysis of oligomers/polymers into their constituent monomers would be favored over the condensation of individual monomers into polymers.
The deep sea vent theory
The deep sea vent, or hydrothermal vent, theory for the origin of life on Earth posits that life may have begun at submarine hydrothermal vents, where hydrogen-rich fluids emerge from below the sea floor and interface with carbon dioxide-rich ocean water. Sustained chemical energy in such systems is derived from redox reactions, in which electron donors, such as molecular hydrogen, react with electron acceptors, such as carbon dioxide (see iron-sulfur world theory).
Fox's experiments
In the 1950s and 1960s, Sidney W. Fox studied the spontaneous formation of peptide structures under conditions that might plausibly have existed early in Earth's history. He demonstrated that amino acids could spontaneously form small peptides. These amino acids and small peptides could be encouraged to form closed spherical membranes, called microspheres.[29]
Eigen's hypothesis
In the early 1970s the problem of the origin of life was approached by Manfred Eigen and Peter Schuster of the Max Planck Institute for Biophysical Chemistry. They examined the transient stages between the molecular chaos and a self-replicating hypercycle in a prebiotic soup.[30]
In a hypercycle, the information storing system (possibly RNA) produces an enzyme, which catalyzes the formation of another information system, in sequence until the product of the last aids in the formation of the first information system. Mathematically treated, hypercycles could create quasispecies, which through natural selection entered into a form of Darwinian evolution. A boost to hypercycle theory was the discovery that RNA, in certain circumstances forms itself into ribozymes, capable of catalyzing their own chemical reactions.[31] However, these reactions are limited to self-excisions (in which a longer RNA molecule becomes shorter), and much rarer small additions that are incapable of coding for any useful protein. The hypercycle theory is further degraded since the hypothetical RNA would require the existence of complex biochemicals such as nucleotides which are not formed under the conditions proposed by the Miller-Urey experiment.
Wächtershäuser's hypothesis
Main article: iron-sulfur world theory
Deep-sea black smoker
Another possible answer to this polymerization conundrum was provided in 1980s by Günter Wächtershäuser, in his iron-sulfur world theory. In this theory, he postulated the evolution of (bio)chemical pathways as fundamentals of the evolution of life. Moreover, he presented a consistent system of tracing today's biochemistry back to ancestral reactions that provide alternative pathways to the synthesis of organic building blocks from simple gaseous compounds.
In contrast to the classical Miller experiments, which depend on external sources of energy (such as simulated lightning or UV irradiation), "Wächtershäuser systems" come with a built-in source of energy, sulfides of iron and other minerals (e.g. pyrite). The energy released from redox reactions of these metal sulfides is not only available for the synthesis of organic molecules, but also for the formation of oligomers and polymers. It is therefore hypothesized that such systems may be able to evolve into autocatalytic sets of self-replicating, metabolically active entities that would predate the life forms known today.
The experiment produced a relatively small yield of dipeptides (0.4% to 12.4%) and a smaller yield of tripeptides (0.10%) but the authors also noted that: "under these same conditions dipeptides hydrolysed rapidly."[32]
Radioactive beach hypothesis
Zachary Adam[33] at the University of Washington, Seattle, claims that stronger tidal processes from a much closer moon may have concentrated grains of uranium and other radioactive elements at the high water mark on primordial beaches where they may have been responsible for generating life's building blocks. According to computer models reported in Astrobiology, vol 7 p 852, a deposit of such radioactive materials could show the same self-sustaining nuclear reaction as that found in the Oklo uranium ore seam in Gabon. Such radioactive beach sand provides sufficient energy to generate organic molecules, such as amino acids and sugars from acetonitrile in water. Radioactive monazite also releases soluble phosphate into regions between sand-grains, making it biologically "accessible". Thus amino acids, sugars and soluble phosphates can all be simultaneously produced, according to Adam. Radioactive actinides, then in greater concentrations, could have formed part of organo-metallic complexes. These complexes could have been important early catalysts to living processes.
John Parnell of the University of Aberdeen suggests that such a process could provide part of the "crucible of life" on any early wet rocky planet, so long as the planet is large enough to have generated a system of plate tectonics which brings radioactive minerals to the surface. As the early Earth is believed to have many smaller "platelets" it would provide a suitable environment for such processes.[34]
Models to explain homochirality
Main article: Homochirality
Some process in chemical evolution must account for the origin of homochirality, i.e. all building blocks in living organisms having the same "handedness" (amino acids being left-handed, nucleic acid sugars (ribose and deoxyribose) being right-handed, and chiral phosphoglycerides). Chiral molecules can be synthesized, but in the absence of a chiral source or a chiral catalyst are formed in a 50/50 mixture of both enantiomers. This is called a racemic mixture. Clark has suggested that homochirality may have started in space, as the studies of the amino acids on the Murchison meteorite showed L-alanine to be more than twice as frequent as its D form, and L-glutamic acid was more than 3 times prevаlent than its D counterpart. It is suggested that polarised light has the power to destroy one enantiomer within the proto-planetary disk. Noyes[35] showed that beta decay caused the breakdown of D-leucine, in a racemic mixture, and that the presence of 14C, present in larger amounts in organic chemicals in the early Earth environment, could have been the cause. Robert M. Hazen reports upon experiments conducted in which various chiral crystal surfaces act as sites for possible concentration and assembly of chiral monomer units into macromolecules[36]. Once established, chirality would be selected for.[37] Work with organic compounds found on meteorites tends to suggest that chirality is a characteristic of abiogenic synthesis, as amino acids show a left-handed bias, whereas sugars show a predominantly right-handed bias.[38]
Self-organization and replication
Main article: Self-organization
While features of self-organization and self-replication are often considered the hallmark of living systems, there are many instances of abiotic molecules exhibiting such characteristics under proper conditions. For example Martin and Russel show that physical compartmentation by cell membranes from the environment and self-organization of self-contained redox reactions are the most conserved attributes of living things, and they argue therefore that inorganic matter with such attributes would be life's most likely last common ancestor.[39]
Virus self-assembly within host cells has implications for the study of the origin of life,[40] as it lends further credence to the hypothesis that life could have started as self-assembling organic molecules.[41]
From organic molecules to protocells
The question "How do simple organic molecules form a protocell?" is largely unanswered but there are many hypotheses. Some of these postulate the early appearance of nucleic acids ("genes-first") whereas others postulate the evolution of biochemical reactions and pathways first ("metabolism-first"). Recently, trends are emerging to create hybrid models that combine aspects of both.
"Genes first" models: the RNA world
Main article: RNA world hypothesis
The RNA world hypothesis, which has gained wide acceptance, describes an early Earth with self-replicating and catalytic RNA but no DNA or proteins. This has spurred scientists to try to determine if relatively short RNA molecules could have spontaneously formed that were capable of catalyzing their own continuing replication.[42] A number of hypotheses of modes of formation have been put forward. Early cell membranes could have formed spontaneously from proteinoids, protein-like molecules that are produced when amino acid solutions are heated – when present at the correct concentration in aqueous solution, these form microspheres which are observed to behave similarly to membrane-enclosed compartments. Other possibilities include systems of chemical reactions taking place within clay substrates or on the surface of pyrite rocks. Factors supportive of an important role for RNA in early life include its ability to act both to store information and catalyse chemical reactions (as a ribozyme); its many important roles as an intermediate in the expression and maintenance of the genetic information (in the form of DNA) in modern organisms; and the ease of chemical synthesis of at least the components of the molecule under conditions approximating the early Earth. Relatively short RNA molecules which can duplicate others have been artificially produced in the lab.[43]
Researchers have pointed out difficulties for the abiotic synthesis of nucleotides from cytosine and uracil.[44] Cytosine has a half-life of 19 days at 100 °C and 17,000 years in freezing water.[45] Larralde et al, say that "the generally accepted prebiotic synthesis of ribose, the formose reaction, yields numerous sugars without any selectivity."[46] and they conclude that their "results suggest that the backbone of the first genetic material could not have contained ribose or other sugars because of their instability." The ester linkage of ribose and phosphoric acid in RNA is known to be prone to hydrolysis.[47]
A slightly different version of this hypothesis is that a different type of nucleic acid, such as PNA, TNA or GNA, was the first one to emerge as a self-reproducing molecule, to be replaced by RNA only later.[48][49]
"Metabolism first" models: iron-sulfur world and others
Several models reject the idea of the self-replication of a "naked-gene" and postulate the emergence of a primitive metabolism which could provide an environment for the later emergence of RNA replication.
One of the earliest incarnations of this idea was put forward in 1924 with Aleksandr Ivanovich Oparin's notion of primitive self-replicating vesicles which predated the discovery of the structure of DNA. More recent variants in the 1980s and 1990s include Günter Wächtershäuser's iron-sulfur world theory and models introduced by Christian de Duve based on the chemistry of thioesters. More abstract and theoretical arguments for the plausibility of the emergence of metabolism without the presence of genes include a mathematical model introduced by Freeman Dyson in the early 1980s and Stuart Kauffman's notion of collectively autocatalytic sets, discussed later in that decade.
However, the idea that a closed metabolic cycle, such as the reductive citric acid cycle, could form spontaneously (proposed by Günter Wächtershäuser) remains debated. In an article entitled "Self-Organizing Biochemical Cycles",[50] the late Leslie Orgel summarized his analysis of the proposal by stating, "There is at present no reason to expect that multistep cycles such as the reductive citric acid cycle will self-organize on the surface of FeS/FeS2 or some other mineral." It is possible that another type of metabolic pathway was used at the beginning of life. For example, instead of the reductive citric acid cycle, the "open" acetyl-CoA pathway (another one of the five recognised ways of carbon dioxide fixation in nature today) would be compatible with the idea of self-organisation on a metal sulfide surface. The key enzyme of this pathway, carbon monoxide dehydrogenase/acetyl-CoA synthase harbours mixed nickel-iron-sulfur clusters in its reaction centers and catalyses the formation of acetyl-CoA (which may be regarded as a modern form of acetyl-thiol) in a single step.
Possible role of bubbles
Waves breaking on the shore create a delicate foam composed of bubbles. Winds sweeping across the ocean have a tendency to drive things to shore, much like driftwood collecting on the beach. It is possible that organic molecules were concentrated on the shorelines in much the same way. Shallow coastal waters also tend to be warmer, further concentrating the molecules through evaporation. While bubbles composed mostly of water burst quickly, water containing amphiphiles forms much more stable bubbles, lending more time to the particular bubble to perform these crucial reactions.
Amphiphiles are oily compounds containing a hydrophilic head on one or both ends of a hydrophobic molecule. Some amphiphiles have the tendency to spontaneously form membranes in water. A spherically closed membrane contains water and is a hypothetical precursor to the modern cell membrane. If a protein would increase the integrity of its parent bubble, that bubble had an advantage, and was placed at the top of the natural selection waiting list. Primitive reproduction can be envisioned when the bubbles burst, releasing the results of the 'experiment' into the surrounding medium. Once enough of the 'right stuff' was released into the medium, the development of the first prokaryotes, eukaryotes, and multicellular organisms could be achieved.[51]
Similarly, bubbles formed entirely out of protein-like molecules, called microspheres, will form spontaneously under the right conditions. But they are not a likely precursor to the modern cell membrane, as cell membranes are composed primarily of lipid compounds rather than amino-acid compounds (for types of membrane spheres associated with abiogenesis, see protobionts, micelle, coacervate).
A recent model by Fernando and Rowe[52] suggests that the enclosure of an autocatalytic non-enzymatic metabolism within protocells may have been one way of avoiding the side-reaction problem that is typical of metabolism first models.
Other models
Autocatalysis
British ethologist Richard Dawkins wrote about autocatalysis as a potential explanation for the origin of life in his 2004 book The Ancestor's Tale. Autocatalysts are substances which catalyze the production of themselves, and therefore have the property of being a simple molecular replicator. In his book, Dawkins cites experiments performed by Julius Rebek and his colleagues at the Scripps Research Institute in California in which they combined amino adenosine and pentafluorophenyl ester with the autocatalyst amino adenosine triacid ester (AATE). One system from the experiment contained variants of AATE which catalysed the synthesis of themselves. This experiment demonstrated the possibility that autocatalysts could exhibit competition within a population of entities with heredity, which could be interpreted as a rudimentary form of natural selection.
Clay theory
A model for the origin of life based on clay was forwarded by Dr A. Graham Cairns-Smith of the University of Glasgow in 1985 and adopted as a plausible illustration by several other scientists, including Richard Dawkins. Clay theory postulates that complex organic molecules arose gradually on a pre-existing, non-organic replication platform — silicate crystals in solution. Complexity in companion molecules developed as a function of selection pressures on types of clay crystal is then exapted to serve the replication of organic molecules independently of their silicate "launch stage".
Cairns-Smith is a staunch critic of other models of chemical evolution.[53] However, he admits, that like many models of the origin of life, his own also has its shortcomings (Horgan 1991).
In 2007, Kahr and colleagues reported their experiments to examine the idea that crystals can act as a source of transferable information, using crystals of potassium hydrogen phthalate. "Mother" crystals with imperfections were cleaved and used as seeds to grow "daughter" crystals from solution. They then examined the distribution of imperfections in the crystal system and found that the imperfections in the mother crystals were indeed reproduced in the daughters. The daughter crystals had many additional imperfections. For a gene-like behavior the additional imperfections should be much less than the parent ones, thus Kahr concludes that the crystals "were not faithful enough to store and transfer information form one generation to the next".[54][55]
Gold's "Deep-hot biosphere" model
In the 1970s, Thomas Gold proposed the theory that life first developed not on the surface of the Earth, but several kilometers below the surface. The discovery in the late 1990s of nanobes (filamental structures that are smaller than bacteria, but that may contain DNA in deep rocks) [56] might be seen as lending support to Gold's theory.
It is now reasonably well established that microbial life is plentiful at shallow depths in the Earth (up to five kilometers below the surface)[56] in the form of extremophile archaea, rather than the better-known eubacteria (which live in more accessible conditions). It is claimed that discovery of microbial life below the surface of another body in our solar system would lend significant credence to this theory. Thomas Gold also asserted that a trickle of food from a deep, unreachable, source is needed for survival because life arising in a puddle of organic material is likely to consume all of its food and become extinct. Gold's theory is that that flow of food is due to out-gassing of primordial methane from the Earth's mantle; more conventional explanations of the food supply of deep microbes (away from sedimentary carbon compounds) is that the organisms subsist on hydrogen released by an interaction between water and (reduced) iron compounds in rocks
"Primitive" extraterrestrial life
An alternative to Earthly abiogenesis is the hypothesis that primitive life may have originally formed extraterrestrially, either in space or on a nearby planet (Mars). (Note that exogenesis is related to, but not the same as, the notion of panspermia). A supporter of this theory was Francis Crick.
Organic compounds are relatively common in space, especially in the outer solar system where volatiles are not evaporated by solar heating. Comets are encrusted by outer layers of dark material, thought to be a tar-like substance composed of complex organic material formed from simple carbon compounds after reactions initiated mostly by irradiation by ultraviolet light. It is supposed that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth.
An alternative but related hypothesis, proposed to explain the presence of life on Earth so soon after the planet had cooled down, with apparently very little time for prebiotic evolution, is that life formed first on early Mars. Due to its smaller size Mars cooled before Earth (a difference of hundreds of millions of years), allowing prebiotic processes there while Earth was still too hot. Life was then transported to the cooled Earth when crustal material was blasted off Mars by asteroid and comet impacts. Mars continued to cool faster and eventually became hostile to the continued evolution or even existence of life (it lost its atmosphere due to low volcanism); Earth is following the same fate as Mars, but at a slower rate.
Neither hypothesis actually answers the question of how life first originated, but merely shifts it to another planet or a comet. However, the advantage of an extraterrestrial origin of primitive life is that life is not required to have evolved on each planet it occurs on, but rather in a single location, and then spread about the galaxy to other star systems via cometary and/or meteorite impact. Evidence to support the plausibility of the concept is scant, but it finds support in recent study of Martian meteorites found in Antarctica and in studies of extremophile microbes.[57] Additional support comes from a recent discovery of a bacterial ecosytem whose energy source is radioactivity.[58]
A recent experiment led by Jason Dworkin, subjected a frozen mixture of water, methanol, ammonia and carbon monoxide to UV radiation, mimicking conditions found in an extraterrestrial environment. This combination yielded large amounts of organic material that self-organised to form bubbles when immersed in water. Dworkin considered these bubbles to resemble cell membranes that enclose and concentrate the chemistry of life, separating their interior from the outside world.
The bubbles produced in these experiments were between 10 to 40 micrometers, or about the size of red blood cells. Remarkably, the bubbles fluoresced, or glowed, when exposed to UV light. Absorbing UV and converting it into visible light in this way was considered one possible way of providing energy to a primitive cell. If such bubbles played a role in the origin of life, the fluorescence could have been a precursor to primitive photosynthesis. Such fluorescence also provides the benefit of acting as a sunscreen, diffusing any damage that otherwise would be inflicted by UV radiation. Such a protective function would have been vital for life on the early Earth, since the ozone layer, which blocks out the sun's most destructive UV rays, did not form until after photosynthetic life began to produce oxygen.[59]
Lipid World
This theory postulates that the first self-replicating object was lipid-like.[60] It is known that phospholipids form bilayers in water while under agitation– the same structure as in cell membranes. These molecules were not present on early earth, however other amphiphilic long chain molecules also form membranes. Furthermore, these bodies may expand (by insertion of additional lipids), and under excessive expansion may undergo spontaneous splitting which preserves the same size and composition of lipids in the two progenies. The main idea in this theory is that the molecular composition of the lipid bodies is the preliminary way for information storage, and evolution led to the appearance of polymer entities such as RNA or DNA that may store information favorably. Still, no biochemical mechanism has been offered to support the Lipid World theory.
Polyphosphates
The problem with most scenarios of abiogenesis is that the thermodynamic equilibrium of amino acid versus peptides is in the direction of separate amino acids. What has been missing is some force that drives polymerization. The resolution of this problem may well be in the properties of polyphosphates.[61][62] Polyphosphates are formed by polymerization of ordinary monophosphate ions PO4−3. Several mechanisms for such polymerization have been suggested. Polyphosphates cause polymerization of amino acids into peptides. They are also logical precursors in the synthesis of such key biochemical compounds as ATP. A key issue seems to be that calcium reacts with soluble phosphate to form insoluble calcium phosphate (apatite), so some plausible mechanism must be found to keep calcium ions from causing precipitation of phosphate. There has been much work on this topic over the years, but an interesting new idea is that meteorites may have introduced reactive phosphorus species on the early earth.[63]
PAH world hypothesis
Main article: PAH world hypothesis
Other sources of complex molecules have been postulated, including extraterrestrial stellar or interstellar origin. For example, from spectral analyses, organic molecules are known to be present in comets and meteorites. In 2004, a team detected traces of polycyclic aromatic hydrocarbons (PAH's) in a nebula.[64] Those are the most complex molecules so far found in space. The use of PAH's has also been proposed as a precursor to the RNA world in the PAH world hypothesis.[65] The Spitzer Space Telescope has recently detected a star, HH 46-IR, which is forming by a process similar to that by which the sun formed. In the disk of material surrounding the star, there is a very large range of molecules, including cyanide compounds, hydrocarbons, and carbon monoxide. PAHs have also been found all over the surface of galaxy M81, which is 12 million light years away from the Earth, confirming their widespread distribution in space.[66]
Multiple genesis
Different forms of life may have appeared quasi-simultaneously in the early history of Earth.[67] The other forms may be extinct, leaving distinctive fossils through their different biochemistry (e.g., using arsenic instead of phosphorus), survive as extremophiles, or simply be unnoticed through their being analogous to organisms of the current life tree. Hartman[68] for example combines a number of theories together, by proposing that:
The first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic and other dicarboxylic acids. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hotspring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids. If biosynthesis recapitulates biopoesis, then the synthesis of amino acids preceded the synthesis of the purine and pyrimidine bases. Furthermore the polymerization of the amino acid thioesters into polypeptides preceded the directed polymerization of amino acid esters by polynucleotides.
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აი ასეა წარმოსადგენი, ახლა შენ თუ საკუთარი კითხვები გაბნევს ეგ შენი პრობლემაა.
| QUOTE | | უკაცრავად, შენთვის გასაგები ენა არ ყოფილა. ტყუილად არცხვენ ნიკს ჯერ ერთი, პროცესორი ინფორმაციას არ ატარებს. პროცესორი ამუშავებს ბინარულ (ანუ ორობით) 0 და 1 საგან შემდგარ კოდს. ყოველ პროცესორს ესმის მხოლოდ თავისი ენა. როცა იქმნება პოცესორი, მასთან ერთად იქმნება ბრძანებების სია რომელიც ზუსტად ამ პროცესორისთვის არის განკუთვნილი. ორივე ერთად იქმნება, გეიგევი შენე? თუ შექმენი რაღაც პროცესორი და სულ სხვა ენა, არც პროცესორი იმუშავებს და არც მოცემულ ენას ექნება რეალიზაცია. |
თუ იცი რომ პროცესორი არ ატარებს ინფორმაციას რატომ ადარებ გენომს?
ყოველ პროცესორს ესმის ბინარული კოდი, სწორედ ეს არის მისი ენა, ნებისმიერი პროგრამული ენის ბრძანება დადის 0 იანებზე და 1 იანებზე და ის საერთოა როგორც AMD სთვის ისე Pentium თუ Dual Core სთვის! ასე რომ არ იყოს ნებისმიერი პროგრამის ცალკე დაწერა იქნებოდა საჭირო ყველა პროცესორისთვის!
ასე რომ იმ სფეროს გაანებე თავი სადაც დილეტანტი ხარ და რამე უფრო ნორმალური ანალოგია მოიყვანე.
| QUOTE | | ასევეა ცოცხალ უჯრედშიც: უჯრედის დნმ-ს წარმოქმნასთან ერთად უნდა შეიქმნას უამრავი ზუსტად ის ცილა, რაც ამ გენშია კოდირებული და რაც გენის საბოლოო რეპლიკაციას, ტრანსკრიპციას და ტრანსლაციას განაპირობებს. თუ უჯრედში მოათავსებ ერთი სახის გენებს და ამას აურევ ისეთ ცილებს რაც ამ გენის კოდში არ წერია და რაც ვერ ემსახურება მის რეპლიკაციას, ტრანსკრიპციას და ტრნსლაციას, მორჩა მომავალი თაობა-ფაფუ, აღარ იქნება. ასევე მორჩა ასეთი უჯრედის არსებობა მეორე წამს. ხოდა, ზუსტად ეს კითხვა დაგისვი მე: როგორ უნდა მოხდეს შემთხვევითი პროცესის წყალობით ასეთი რამე თქო? როგორ შეიძლება შემთხვევით წრმოიქმნას გენიც და მასთან ერთად ზუსტად ის ცილაც რაც ამ გენში წერია? რა თეორიები არსებობს ამის შესახებ თქო? შენ კიდევ მეტრანახევრიან ლინკებს დებ და უმოწყალოდ მთხოვ მაგ სისულელეების წაკითხვას. მასეთი სისულელე ბევრი მაქვს წაკითხული. ამიტომ, შენ რასაც თვლი რომ მაგ ლინკიდან ჩემს კითხვას პასუხობს, ეგ ციტატა ამოიღე, დადე და ვნახოთ რა არის მართალი და რა არა. |
სამწუხაროდ მოგიწევს ყველა თეორიის წაკითხვა თუკი გაინტერესებს მაგ კითხვაზე პასუხი, თუ კითხვა არ გიყვარს - ეგ შენი პრობლემაა.
| QUOTE | | ფიფქებს რაც შეეხება, მაგას ფიფქია აგზავნის როცა კაი ხასიათზეა. |
რაო არ არის პასუხი ხო? მე მესმის რომ ძალიან გინდა ყველაფერი შენს სურვილებს ესალბუნებოდეს, მაგრამ არ არის მასე  |
იმას ამბობს, რომ დღემდე ცხიმოვანი მჟავების დამაკმაყოფილებელი სინთეზი არ მომხდარა.
ყველაზე კარგი იქნება შევთანხმდეთ იმაზე, რომ საერთოდ მაგის გარკვევა შეუძლებელია. და რაც ყველაზე მთავარია, დარვინიზმის უარყოფა, არ ნიშნავს იმას, რომ მე იმ აზრს ვიზიარებ თითქოს ღმერთის მიერ იყო შექმნილი ეს ყველაფერი, მერე კიდობანში ჩალაგებული და მერე მიმოფანტული ამ დუნიაზე 
და რატომღაც სრულად სინთეტიკურ პოლიომიელიტზე რო არ იღებს ხმას https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1490301/
არაფერი ახალი და განსაკუთრებული მოკლედ. 
