patently this is possibly the second question that can happen to anyone thinking of a second in topics related to biology. All this of atoms and molecular structures is very nice ... but must have arisen from somewhere, right? How is orchestrated to give rise to what today we understand as "life?
The most important evidence on this subject is given by Louis Pasteur, in his famous experiment on the spontaneous origin of life ... essentially showed that If microorganisms are prevented from falling into a flask inverted tip (with sterile culture medium in), no crop could appear in it. As a control experiment (ie, to support the alternative hypothesis) presented a normal tip flask and exposed to air another developed a culture of microorganisms inside. In its simplest form, showed that microorganisms in the air should to cause to fall into life inside the flask and therefore is not spontaneously generated only because the conditions (culture medium) were favorable. The refutation of Pasteur was a revolution in its time and gave rise to the most important question that has become biology ... If all life is based on one life, then, life has always existed?
Although it may seem ridiculous this is an assumption that modern science is still unable to rebut with actual data. So much so that the proposal has curdled into a lot of science and is known as Panspermia hypothesis ("Pan" indicating the whole and "Sperma" meaning seed), in which the seeds of life would be scattered throughout the universe and widespread wherever possible.
Within the modern hypothesis of Panspermia, the origin of life on Earth is supposed to come from Mars (where the meteorite ALH84001 appears to be the only evidence of possible extraterrestrial life clearly in the form of micro-organisms).
modern
The other hypothesis is the Origin of Species by Charles Darwin. In his epitomesca work, Darwin proposed that all species should arise from an earlier, yet there must be a species that is the ancestor of all that we can find. However, Darwin
quickly corrected by saying that it could also be possible for life to have emerged at many different points of the planet and even at different times of life on Earth. But thanks to modern genetic studies, there can be little doubt that all living species and all those known from a single common ancestor (which does not mean that all species that ever existed have come from the same common ancestor) .
modern The other hypothesis is the Origin of Species by Charles Darwin. In his epitomesca work, Darwin proposed that all species should arise from an earlier, yet there must be a species that is the ancestor of all that we can find. However, Darwin
quickly corrected by saying that it could also be possible for life to have emerged at many different points of the planet and even at different times of life on Earth. But thanks to modern genetic studies, there can be little doubt that all living species and all those known from a single common ancestor (which does not mean that all species that ever existed have come from the same common ancestor) . Once the kick of Biology Molecular, the study of the structure of DNA by Watson and Crick in 1953, it seemed logical that there should be a molecular theory of the origin of life. So far, it was known that cells forming of all living organisms, always originating from another cell, a process that was through cell division. Before or after cell division (or mitosis), however, should be clearly a growth-expansion process in the cell acquire the ability to divide without losing gradually the size, components and properties. Moreover, as it was known that the hereditary information of the characters are pierced through the core and, in particular, the hereditary information carried by genes, which in turn were in the DNA, it seemed logical to think that the DNA must be copied / duplicated / replicated, for the cells to "Daughters" would continue to exist . But also, as the characters that were changing were somehow inscribed in the DNA (genes), DNA seemed to be the molecule that actually have "evolved" according to the Darwinian concept, to give rise to the current species.
had to explain however, how the DNA might be capable of faithfully copied so that the characters are kept. Watson and Crick, in the same article 53, scored a hypothesis, called semiconservative replication, which postulated that as each linear strand containing the information to write the supplementary (since the pairing of AT and GC bases or Chargaff rule governing this), double chain could eventually spread to serve each one as a template for the biochemical synthesis of the complementary respectively. This fact would be shown elegantly by Meselson and Stahl in 1958.
As discussed in upcoming entries, also proved the DNA molecule in which the information was coded to guide the cellular production of other biological molecules (nearly all), so it seemed evident that he would be the preferred candidate.
Everything pointed to DNA as the most promising molecule to be the first molecule of life. The other possible competitor RNA, a molecule seemed too unstable to be the origin of anything. In addition, information was encoded RNA into DNA, and RNA was produced only from DNA. However
... it all collapsed with two discoveries, in 1965 and 1981.
had to explain however, how the DNA might be capable of faithfully copied so that the characters are kept. Watson and Crick, in the same article 53, scored a hypothesis, called semiconservative replication, which postulated that as each linear strand containing the information to write the supplementary (since the pairing of AT and GC bases or Chargaff rule governing this), double chain could eventually spread to serve each one as a template for the biochemical synthesis of the complementary respectively. This fact would be shown elegantly by Meselson and Stahl in 1958.
As discussed in upcoming entries, also proved the DNA molecule in which the information was coded to guide the cellular production of other biological molecules (nearly all), so it seemed evident that he would be the preferred candidate.
Everything pointed to DNA as the most promising molecule to be the first molecule of life. The other possible competitor RNA, a molecule seemed too unstable to be the origin of anything. In addition, information was encoded RNA into DNA, and RNA was produced only from DNA. However
... it all collapsed with two discoveries, in 1965 and 1981.
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