The RNA World hypothesis got a big boost in 2009.
and Eric Smith have written up a very nice summary of the Metabolism First hypothesis for ..
The first hypothesis for the origin of life was invented in ..
The RNA world hypothesis, for example, suggests that short molecules could have spontaneously formed that would then catalyze their own continuing replication. Early cell membranes could have formed spontaneously from , protein-like molecules that are produced when amino acid solutions are heated. Other possibilities include systems of chemical reactions taking place within substrates or on the surface of rocks. At this time however, these various hypotheses have incomplete evidence supporting them. Many of them can be simulated and tested in the lab, but a lack of undisturbed sedimentary rock from that early in Earth's history leaves few opportunities to determine what may have actually happened in reality.
It is generally assumed that life had a single origin — or, at least, that all extant life descended from a 'universal common ancestor' (UCA) — although this view has been called into question by evidence for extensive horizontal gene transfer. Here, the UCA view is framed as a formal hypothesis and tested (crucially, without assuming that genetic similarity reflects genetic kinship). The UCA view triumphs: a single origin of life is overwhelmingly more likely than any competing hypothesis.
The first hypothesis for the origin of life was ..
As described above, the GADV hypothesis reasonably explains how the genetic system was created on the primitive Earth. In contrast, it is impossible to find a reasonable explanation for the establishment of the genetic code and creation of genes from the standpoint of the RNA world hypothesis. The reasons are as follows. In addition to frequently stressed weak points that it is quite difficult to synthesize nucleotides, oligonucleotides and RNA under prebiotic conditions, there are a number of other, probably fatal, weak points in the RNA world hypothesis. First, self-replication of RNA is principally impossible, because the replication requires RNA as a template without three-dimensional structure and simultaneously requires RNA with three-dimensional structure for catalytic function. Second, genetic information would never be formed from self-replicated RNA, since the genetic sequence has been always composed of triplet codons, which is never created by random joining of nucleotides one by one. Third, even if the genetic function were created with RNA, the function could not be expressed in the absence of the genetic code. This means that the genetic code must always precede the formation of genetic RNA. Forth, catalytic function of a three-dimensional RNA or ribozyme is never transferred to amino acid sequence of protein with the same function. So, I consider that life never emerged according to the RNA-world prebiotic scenario.
RNA world hypothesis is widely accepted still now, as an idea by which the origin of life might be explained. But, there are many weak points in the hypothesis. In contrast, I have proposed a more reasonable [GADV]-protein world hypothesis or GADV hypothesis, suggesting that life originated from the protein world, which was formed by pseudo-replication of [GADV]-proteins. In this communication, I will discuss about the origin of life from the point of view of the GADV hypothesis.
Metabolism-first hypothesis of the origin of life
By 3.6 to 3.8 billion years ago all of these events had come to pass; the RNA world had fallen and the DNA/protein world had risen in its place.But other researchers see evidence for prokaryotic cells in the first 100 million years, maybe even immediately.
An alternative to Earthly abiogenesis is the hypothesis that primitive life may have originally formed extraterrestrially (note that is related to, but is not the same as the notion of ). Organic compounds are relatively common in space, especially in the outer solar system where volatiles are not evaporated by solar heating. are encrusted by outer layers of dark material, thought to be a -like substance composed of complex organic material formed from simple carbon compounds after reactions initiated mostly by irradiation by light. It is supposed that a rain of cometary material on the early Earth could have brought significant quantities of complex organic molecules, and that it is possible that primitive life itself may have formed in space was brought to the surface along with it. A related hypothesis holds that life may have formed first on early , and been transported to Earth when crustal material was blasted off of Mars by asteroid and comet impacts to later fall to Earth's surface. Both of these hypotheses are even more difficult to find evidence for, and may have to wait for samples to be taken from comets and Mars for study.
The RNA World and other origin-of-life theories. by Brig Klyce
There are plenty of ideas, but few clear facts
and Eric Smith have written up a very nice summary of the Metabolism First hypothesis ..
Origin of Life Theories: Metabolism-first vs
and the one which supports metabolism first is the Protein world hypothesis.
What was the proteins first hypothesis? | Yahoo Answers
RNA world hypothesis, ..
Sandwalk: Metabolism First and the Origin of Life
As the question how organic molecules form a protocell is largely unanswered, there are many different hypotheses regarding the path that might have been taken from simple organic molecules to protocells, cells, and metabolism. Some of these postulate early appearance of nucleic acids ("-first"), whereas the evolution of biochemical reactions and pathways is regarded as moving force of early evolution ("-first"). Recently, trends are emerging to create hybrid models that combine aspects of both.
Metabolism First and the Origin of Life ..
A hypothesis for the origin of life based on was forwarded by Dr A. of in and adopted as a plausible illustration by just a handful of other scientists (including ). postulates complex organic molecules arising 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 to serve the replication of organic molecules independently of their silicate "launch stage".
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