Loncat ke navigasi Loncat ke pencarian Biogenesis adalah produksi kehidupan organisme atau organel baru. Hukum biogenesis, dianggap dicetuskan oleh Louis Pasteur , observasi bahwa benda hidup hanya dapat dihasilkan dari benda hidup yang lain, dengan reproduksi misalnya lalat bertelur, yang menetas menjadi lalat-lalat. Jadi, kehidupan tidak dihasilkan dari benda mati, yaitu teori yang disebut "pembentukan spontan" spontaneous generation. Juga "Omne vivum ex ovo, omne ovum ex vivo" "semua kehidupan berasal dari telur, semua telur berasal dari kehidupan".
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Andrei Kursanov and Alexander Oparin right in No new notable research or hypothesis on the subject appeared until , when Alexander Oparin reasoned that atmospheric oxygen prevents the synthesis of certain organic compounds that are necessary building blocks for life.
In his book The Origin of Life,   he proposed echoing Darwin that the "spontaneous generation of life" that had been attacked by Louis Pasteur did in fact occur once, but was now impossible because the conditions found on the early Earth had changed, and preexisting organisms would immediately consume any spontaneously generated organism. Oparin argued that a "primeval soup" of organic molecules could be created in an oxygenless atmosphere through the action of sunlight.
These would combine in ever more complex ways until they formed coacervate droplets. These droplets would " grow " by fusion with other droplets, and " reproduce " through fission into daughter droplets, and so have a primitive metabolism in which factors that promote "cell integrity" survive, and those that do not become extinct.
Robert Shapiro has summarized the "primordial soup" theory of Oparin and J. Haldane in its "mature form" as follows:  The early Earth had a chemically reducing atmosphere. This atmosphere, exposed to energy in various forms, produced simple organic compounds " monomers ".
These compounds accumulated in a "soup" that may have concentrated at various locations shorelines, oceanic vents etc.
By further transformation, more complex organic polymers —and ultimately life—developed in the soup. Bernal called this idea biopoiesis or biopoesis, the process of living matter evolving from self-replicating but non-living molecules,   and proposed that biopoiesis passes through a number of intermediate stages.
One of the most important pieces of experimental support for the "soup" theory came in Stanley L. Miller and Harold C. 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 reducing mixture of gases— methane , ammonia , and hydrogen , as well as water vapour —to form simple organic monomers such as amino acids. This provided direct experimental support for the second point of the "soup" theory, and it is around the remaining two points of the theory that much of the debate now centres.
Bernal showed that based upon this and subsequent work there is no difficulty in principle in forming most of the molecules we recognize as the necessary molecules for life from their inorganic precursors. The underlying hypothesis held by Oparin, Haldane, Bernal, Miller and Urey, for instance, was that multiple conditions on the primeval Earth favoured chemical reactions that synthesized the same set of complex organic compounds from such simple precursors.
A reanalysis of the saved vials containing the original extracts that resulted from the Miller and Urey experiments, using current and more advanced analytical equipment and technology, has uncovered more biochemicals than originally discovered in the s. One of the more important findings was 23 amino acids, far more than the five originally found. In one of his experiments, he allowed amino acids to dry out as if puddled in a warm, dry spot in prebiotic conditions.
He found that, as they dried, the amino acids formed long, often cross-linked, thread-like, submicroscopic polypeptide molecules now named " proteinoid microspheres ". He placed lumps of lava over amino acids derived from methane, ammonia and water, sterilized all materials, and baked the lava over the amino acids for a few hours in a glass oven.
A brown, sticky substance formed over the surface, and when the lava was drenched in sterilized water, a thick, brown liquid leached out. The amino acids had combined to form proteinoids , and the proteinoids had combined to form small globules that Fox called "microspheres". His proteinoids were not cells, although they formed clumps and chains reminiscent of cyanobacteria , but they contained no functional nucleic acids or any encoded information.
Based upon such experiments, Colin S. Pittendrigh stated in December that "laboratories will be creating a living cell within ten years," a remark that reflected the typical contemporary naivety about the complexity of cell structures.
Scientists have proposed several plausible hypotheses, which share some common elements. While differing in the details, these hypotheses are based on the framework laid out by Alexander Oparin in and by J. Haldane in , that the first molecules constituting the earliest cells "were synthesized under natural conditions by a slow process of molecular evolution, and these molecules then organized into the first molecular system with properties with biological order".
According to later models, the atmosphere in the late Hadean period consisted largely of nitrogen N2 and carbon dioxide, with smaller amounts of carbon monoxide, hydrogen H2 , and sulfur compounds;  while it did lack molecular oxygen and ozone,  it was not as chemically reducing as Oparin and Haldane supposed. Bernal coined the term biopoiesis in to refer to the origin of life. Modern work on the way that cell membranes self-assemble, and the work on micropores in various substrates, may be a key step towards understanding the development of independent free-living cells.
Both Manfred Eigen and Sol Spiegelman demonstrated that evolution, including replication, variation, and natural selection , can occur in populations of molecules as well as in organisms. Without such a proof-of-principle, explanations have tended to focus on chemosynthesis. Others have argued that a " top-down approach " is more feasible.
Spiegelman took advantage of natural selection to synthesize the Spiegelman Monster , which had a genome with just nucleotide bases, having deconstructively evolved from a base bacterial RNA. Craig Venter Institute engineered existing prokaryotic cells with progressively fewer genes, attempting to discern at which point the most minimal requirements for life are reached.
The advent of polymers that could replicate, store genetic information, and exhibit properties subject to selection likely was a critical step in the emergence of prebiotic chemical evolution. Based on recent computer model studies , the complex organic molecules necessary for life may have formed in the protoplanetary disk of dust grains surrounding the Sun before the formation of the Earth.
Also see Extraterrestrial organic molecules. Estimates of the production of organics from these sources suggest that the Late Heavy Bombardment before 3.
Simulations of geothermically heated oceanic crust yield far more organics than those found in the Miller-Urey experiments. In the deep hydrothermal vents , Everett Shock has found "there is an enormous thermodynamic drive to form organic compounds, as seawater and hydrothermal fluids, which are far from equilibrium, mix and move towards a more stable state. Stan Palasek suggested based on a theoretical model that self-assembly of ribonucleic acid RNA molecules can occur spontaneously due to physical factors in hydrothermal vents.
For example, heat such as from geothermal processes is a standard energy source for chemistry. Other examples include sunlight and electrical discharges lightning , among others.
For example, this was probably important for carbon fixation the conversion of carbon from its inorganic form to an organic one. Iron-sulfur surfaces, which are abundant near hydrothermal vents, are also capable of producing small amounts of amino acids and other biological metabolites. In particular, experiments by Butlerov the formose reaction showed that tetroses, pentoses, and hexoses are produced when formaldehyde is heated under basic conditions with divalent metal ions like calcium.
The reaction was scrutinized and subsequently proposed to be autocatalytic by Breslow in Similar experiments see below demonstrate that nucleobases like guanine and adenine could be synthesized from simple carbon and nitrogen sources like hydrogen cyanide and ammonia. Formamide produces all four ribonucleotides and other biological molecules when warmed in the presence of various terrestrial minerals.
Formamide is ubiquitous in the Universe, produced by the reaction of water and hydrogen cyanide HCN. It has several advantages as a biotic precursor, including the ability to easily become concentrated through the evaporation of water. It can play roles in other chemical processes as well, such as the synthesis of the amino acid glycine.
Orgel and colleagues have shown that freezing temperatures are advantageous for the synthesis of purines, due to the concentrating effect for key precursors such as hydrogen cyanide. Miller and colleagues suggested that while adenine and guanine require freezing conditions for synthesis, cytosine and uracil may require boiling temperatures.
As an ice crystal forms, it stays pure: only molecules of water join the growing crystal, while impurities like salt or cyanide are excluded. These impurities become crowded in microscopic pockets of liquid within the ice, and this crowding causes the molecules to collide more often.
Mechanistic exploration using quantum chemical methods provide a more detailed understanding of some of the chemical processes involved in chemical evolution, and a partial answer to the fundamental question of molecular biogenesis. However, current scientific consensus describes the primitive atmosphere as either weakly reducing or neutral   see also Oxygen Catastrophe. Such an atmosphere would diminish both the amount and variety of amino acids that could be produced, although studies that include iron and carbonate.
Spontaneous generation and its disproof[ edit ] Main article: Spontaneous generation The Ancient Greeks believed that living things could spontaneously come into being from nonliving matter, and that the goddess Gaia could make life arise spontaneously from stones — a process known as Generatio spontanea. Aristotle disagreed, but he still believed that creatures could arise from dissimilar organisms or from soil. Variations of this concept of spontaneous generation still existed as late as the 17th century, but towards the end of the 17th century, a series of observations and arguments began that eventually discredited such ideas. This advance in scientific understanding was met with much opposition, with personal beliefs and individual prejudices often obscuring the facts. William Harvey — was an early proponent of all life beginning from an egg, omne vivum ex ovo. Francesco Redi , an Italian physician, proved as early as that higher forms of life did not originate spontaneously by demonstrating that maggots come from eggs of flies. Attempts to disprove the spontaneous generation of life from non-life continued in the early 19th century with observations and experiments by Franz Schulze and Theodor Schwann.
Difference Between Abiogenesis and Biogenesis
Andrei Kursanov and Alexander Oparin right in No new notable research or hypothesis on the subject appeared until , when Alexander Oparin reasoned that atmospheric oxygen prevents the synthesis of certain organic compounds that are necessary building blocks for life. In his book The Origin of Life,   he proposed echoing Darwin that the "spontaneous generation of life" that had been attacked by Louis Pasteur did in fact occur once, but was now impossible because the conditions found on the early Earth had changed, and preexisting organisms would immediately consume any spontaneously generated organism. Oparin argued that a "primeval soup" of organic molecules could be created in an oxygenless atmosphere through the action of sunlight. These would combine in ever more complex ways until they formed coacervate droplets. These droplets would " grow " by fusion with other droplets, and " reproduce " through fission into daughter droplets, and so have a primitive metabolism in which factors that promote "cell integrity" survive, and those that do not become extinct. Robert Shapiro has summarized the "primordial soup" theory of Oparin and J. Haldane in its "mature form" as follows:  The early Earth had a chemically reducing atmosphere.
Apakah perbedaan Abiogenesis dan Biogenesis? Asal usul kehidupan adalah topik yang kontroversial dan juga memiliki sejarah panjang. Orang kuno percaya bahwa asal usul kehidupan adalah mekanisme spontan dan terjadi karena zat tak hidup. Abiogenesis Abiogenesis adalah kepercayaan kuno tentang asal usul kehidupan. Hal ini juga dikenal sebagai teori generasi spontan kehidupan. Teori abiogenesis menyatakan bahwa asal-usul makhluk hidup adalah karena zat tak hidup, atau itu adalah insiden spontan. Namun, sampai sekarang para ilmuwan telah mampu mencapai teori ini dengan eksperimen.
Perbedaan antara Abiogenesis dan Biogenesis
The atmospheric gases of the primitive earth were induced by lightning and other sources of energy to react with each other, forming simple organic compounds monomers. Subsequent self-assembling of these simple organic compounds formed the complex organic compounds polymers such as carbohydrates and proteins. These, in turn, might organize into living cells by themselves. Figure 1: Alexander Oparin right in his lab Miller-Urey Experiment Stanley Miller and Harold Urey conducted an experiment, attempting to simulate the conditions of the primitive earth atmosphere. At the bottom of a flask, water was boiled into vapor, and then the vapor was passed through an apparatus, combining with hydrogen , ammonia , and methane gases.