For many scientists in the origin-of-life field, those shadows had lifted two decades earlier with the discovery of ribozymes, enzyme-like substances made of RNA. A simple solution to the chicken-and-egg riddle now appeared to fall into place: Life began with the appearance of the first RNA molecule. In a germinal 1986 article, Nobel Laureate Walter Gilbert of Harvard University wrote in the journal Nature: "One can contemplate an RNA world, containing only RNA molecules that serve to catalyze the synthesis of themselves. & The first step of evolution proceeds then by RNA molecules performing the catalytic activities necessary to assemble themselves from a nucleotide soup." In this vision, the first self-replicating RNA that emerged from non-living matter carried out the functions now executed by RNA, DNA and proteins.
A number of additional clues seemed to support the idea that RNA appeared before proteins and DNA in the evolution of life. Many small molecules, called cofactors, play a necessary role in enzyme-catalyzed reactions. These cofactors often carry an attached RNA nucleotide with no obvious function. These structures have been considered "molecular fossils," relics descended from the time when RNA alone, without DNA or proteins, ruled the biochemical world. In addition, chemists have been able to synthesize new ribozymes that display a variety of enzyme-like activities. Many scientists found the idea of an organism that relied on ribozymes, rather than protein enzymes, very attractive.
The hypothesis that life began with RNA was presented as a likely reality, rather than a speculation, in journals, textbooks and the media. Yet the clues I have cited only support the weaker conclusion that RNA preceded DNA and proteins; they provide no information about the origin of life, which may have involved stages prior to the RNA world in which other living entities ruled supreme. Just the same, and despite the difficulties that I will discuss in the next section, perhaps two-thirds of scientists publishing in the origin-of life field (as judged by a count of papers published in 2006 in the journal Origins of Life and Evolution of the Biosphere) still support the idea that life began with the spontaneous formation of RNA or a related self-copying molecule. Confusingly, researchers use the term "RNA World" to refer to both the strong and the weak claims about RNA's role prior to DNA and proteins. Here, I will use the term "RNA first" for the strong claim that RNA was involved in the origin of life.
The Soup Kettle is Empty
The attractive features of RNA World prompted Gerald Joyce of the Scripps Research Institute and Leslie Orgel of the Salk Institute to picture it as "the molecular biologist's dream" within a volume devoted to that topic. They also used the term "the prebiotic chemist's nightmare" to describe another part of the picture: How did that first self-replicating RNA arise? Enormous obstacles block Gilbert's picture of the origin of life, sufficient to provoke another Nobelist, Christian De Duve of Rockefeller University, to ask rhetorically, "Did God make RNA?"
RNA's building blocks, nucleotides, are complex substances as organic molecules go. They each contain a sugar, a phosphate and one of four nitrogen-containing bases as sub-subunits. Thus, each RNA nucleotide contains 9 or 10 carbon atoms, numerous nitrogen and oxygen atoms and the phosphate group, all connected in a precise three-dimensional pattern. Many alternative ways exist for making those connections, yielding thousands of plausible nucleotides that could readily join in place of the standard ones but that are not represented in RNA. That number is itself dwarfed by the hundreds of thousands to millions of stable organic molecules of similar size that are not nucleotides.
The RNA nucleotides are familiar to chemists because of their abundance in life and their resulting commercial availability. In a form of molecular vitalism, some scientists have presumed that nature has an innate tendency to produce life's building blocks preferentially, rather than the hordes of other molecules that can also be derived from the rules of organic chemistry. This idea drew inspiration from a well known experiment published in 1953 by Stanley Miller. He applied a spark discharge to a mixture of simple gases that were then thought to represent the atmosphere of the early Earth. Two amino acids of the set of 20 used to construct proteins were formed in significant quantities, with others from that set present in small amounts. (A description of the Miller experiment and the chemical structures of an amino acid and a nucleotide can be found in "The Origin of Life on the Earth," by L. E. Orgel; Scientific American, October 1994.) In addition, more than 80 different amino acids, some present and others absent from living systems, have been identified as components of the Murchison meteorite, which fell in Australia in 1969. Nature has apparently been generous in providing a supply of these particular building blocks. By extrapolation of these results, some writers have presumed that all of life's building could be formed with ease in Miller-type experiments and were present in meteorites and other extraterrestrial bodies. This is not the case.
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11 Comments
Add CommentHomeopatics as an Energy Network -
Reply | Report Abuse | Link to thisOne can conjecture that as in the human body just one germ can produce a large colony, also really
small quantities of homeopatic moleclules "reproduce" to larger amounts in cells and tissues (energy networks).
May be only just for small times but enough to induce health
benefits.
hope to hear your opinions
Marco Magagnini, Ph.D - Milan
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Edited by Marco Maga at 12/03/2007 11:05 AM
Do you see prions, which are arguably heritable material in the absence of nucleic acids, as supporting the theory of metabolism first?
Reply | Report Abuse | Link to thisThis is my opinion of life:
Reply | Report Abuse | Link to thisOur universe is like a rugby ball and v r just a dot moving across it from the starting point of the Big Bang n now it's moving towards the end of the universe at an accelerating pace (Dark forces). There is an evidence of the accelerating Dark Forces by some of the scientists' observation: the Milky Way Galaxy is getting apart from the nearest galaxy (Andromeda) at an increasing distance. But im not that agree wif this comment. The reason of our galaxy is getting further apart wif the other galaxy may be due to differences in masses. The Andromeda Galaxy may has a higher mass than our Milky Way n since both of the galaxy is moving in the vacuum condition, it will result in an increasing interval of distance.
(Assume there's a multiverse)
When the galaxies is moving toward the end of the universe, everything will move faster n faster in the vacuum condition n results in the speed of greater than light. When this occurs, an extremely high gravitivity forces created and then everything will move in a slow pace n crushed into a single point like a melting pot. Wat will happen next? A massive blackhole will be created n everything like our galaxy will be sucked into it and causes a new Big Bang in the other dimension of universe. There it goes, everything starts again in the new dimension of universe! If this is true, life is just like a cycle. We will bcome ourselves again for infinitive times!
My conclusion is: Life is not simply created for no reason so as the Big bang theory. Everything is not simply pop out or exist for no reason! If those DNA n RNA theories of origin of life r used to prove the creation of life, it may make sense. But it's still not enuf evidences to prove "why u r you, not me?" "why i am myself, not u?"... There's no such answer yet till now on the scientific aspect. If u r not convinced wif the above statement, be optimistic. If u r given life for being u now, there will be another time that u will be given life again to become other things else!
prions are know to assume the beta amyloid structure.......and they are NOT SELF Replicated.When there is pressure with normal proteins...the normal ones turn into the amyloid form.(Thats not what you call self..is it?)
Reply | Report Abuse | Link to thisI consider them as malformed proteins that did not get eliminated because of their ability to convert normal proteins to amyloid form.
Life's Manifest
Reply | Report Abuse | Link to thisRecapitulation of some earlier notes on
The Drive, Nature And Purpose Of Life: Scientific Comprehension
http://www.physforum.com/index.php?showtopic=14988&st=195&#entry330517
A. Uniqueness Of science among human artifacts
ALL aspects of our culture are, of course, anthropoartifacts, including science. Yet among those artifacts science has a distinct uniqueness for us.
During the recent several centuries in the course of human history humans have been developing science at an accelerating rate as a provider of convincing, ever closer approaching, approximate models of the real world.
B. The drive and nature of life
The drive of life and of its evolution is to enhance the functionality and survivability of the genes, in order to maintain and enhance Earth-biosphere's temporary constrained energy storage and to maintain it BIO as long as possible.
It is the genes, life's prime strata organisms, that evolve, and the evolution of genomes, the 2nd stratum of life, and of the 3rd life stratum cellular organisms, is an interenhancing consequence of their genes' evolution.
C. The nature of life
Earth Life: 1. a format of temporarily constrained energy, retained in temporary constrained genetic energy packages in forms of genes, genomes and organisms 2. a real virtual affair that pops in and out of existence in its matrix, which is the energy constrained in Earth's biosphere.
Earth organism: a temporary self-replicable constrained-energy genetic system that supports and maintains Earth's biosphere by maintenance of genes.
Gene: a primal Earth's organism. (1st stratum organism)
Genome: a multigenes organism consisting of a cooperative commune of its member genes. (2nd stratum organism)
Cellular organisms: mono- or multi-celled earth organisms. (3rd stratum organism)
D. Update of underlying life sciences conception is thus feasible
- First were independent individual genes, Earth's primal organisms.
- Genes aggregated cooperatively into genomes, multigenes organisms, with genomes' organs.
- Simultaneously or consequently genomes evolved protective and functional membranes, organs.
- Then followed cellular organisms, with a variety of outer-cell membrane shapes and
functionalities.
This conception is a scientific, NOT TECHNOLOGICAL, life-science innovation.
It is tomorrow's comprehension of life and of its evolution.
IT IS FRAUGHT WITH INTRIGUING DARWINIAN EVOLUTION IMPLICATIONS.
IT IS FRAUGHT WITH INTRIGUING TECHNOLOGICAL DEVELOPMENTS POTENTIALS.
E. The purpose of OUR, human, life
The purpose of OUR life and its promotion is ours to formulate and set. It derives solely from our cognition.
Suggesting,
Dov Henis
http://blog.360.yahoo.com/blog-P81pQcU1dLBbHgtjQjxG_Q--?cq=1
Very informative article when it comes down to understanding the way proteins are a functional unit in life.
Reply | Report Abuse | Link to thisSo far the best alternative hypothesis I've read on the topic of life's origins.
Reply | Report Abuse | Link to thisI have a suggestion for testing this hypothesis with experiments: it is probably safe to assume that our planet has been on a 24 hour cycle due to it's rotation and the distance from the sun probably hasn't changed much; the sun probably contributed to numerous UV or heat induced reactions on the Earth's surface. Most living things on this planet adhere to the 24 (+variation) hour cycle, the circadian rhythm (with the exception of some cyanobacteria and deep sea species, not sure about this). there are probably many slow-acting reactions, i.e., those with roughly a 24 hour cycle that can be tested in the lab for a cyclical pattern. In fact, they do not have to be 24 hours to test the stated hypothesis given that any cycle can lead to the development of an organized pattern. Given that this state of the planet's environment probably hasn't changed drastically (e.g., from a 100 hour day), it is probable that the earliest cycles were 24 hour based.
comments welcome.
MEch
-origin of life huh, i don't know but writing and assignment on this really helped me out to grasp the concepts of the requirements of life and the difference between "small molecules" that might have started life or "RNA first". Long article but got a point across....
Reply | Report Abuse | Link to thisI wonder how the history of the Solar System and the Earth/Moon pair could colour our understanding of this process.
Reply | Report Abuse | Link to thisI would expect the frequent, violent tides of hot water during the early life of the Earth,when the Moon was very close and the Earth was cool enough for water to condense and accumulate, would provide an vigorous environment for rapid evolution and distribution of the chemical building blocks for 'life'. But would the level of complexity that could develop at that time be constrained by these same conditions.
The latest theories seem to suggest that both the large, influential moon and the water arrived on the Earth by impact. What are the chances of this happening in such a way and at such a time that they were not absorbed or distributed, but remained localised enough to have the observed impact on the Earth.
Could the resulting conditions and their impact on 'life' be so rare as to be almost unique?
How would life have developed without the mixing & distribution possible in a large body of well-stirred, hot, volitile liquid? Could it have survived an "extinction-event" meteor impact, for example?
Unbelievable! Origin Of Life Pre-Metabolism?
Reply | Report Abuse | Link to thisThe Wheel has Just Been Reinvented!
Read All About It!
What Came First in the Origin of Life? New Study Contradicts the 'Metabolism First' Hypothesis
http://www.sciencedaily.com/releases/2010/01/100108101433.htm
Dov Henis
(Comments From The 22nd Century)
Updated Life's Manifest May 2009
http://www.the-scientist.com/community/posts/list/140/122.page#2321
28Dec09 Implications Of E=Total[m(1 + D)]
http://www.the-scientist.com/community/posts/list/184.page#4587
Cosmic Evolution Simplified
http://www.the-scientist.com/community/posts/list/240/122.page#4427
PS: Just reflect about sleep and chirality... DH
I am surprised that this research has not yet attracted a mass of religious zealots who are horrified that humans are trying to take over God's primary feat - the creation of life. This hubris can result in nothing less than what happened to those who constructed the Tower of Babel, stuff like that. Anyway, I hope I live to see my fellow humans achieve this goal. For now, I carry a card in my wallet that says: I am an atheist. In case for accident call a doctor
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