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Darwin · 6 juli 2003, 21:16

De aminozuren lijken in de ruimte synthetiseerd te worden en komen dan via meteoren en mereorieten op de planeten terecht.

NASA SCIENTISTS CREATE AMINO ACIDS IN DEEP-SPACE-LIKE ENVIRONMENT

NASA scientists today announced the creation of amino acids, critical for life, in an environment that mimics deep space. The research will be published in the March 28 issue of the journal Nature.

In a laboratory at NASA Ames Research Center in California’s Silicon Valley, the team of astrobiologists shone ultraviolet light on deep-space-like "ices," simulating conditions that are commonplace in interstellar space. Deep-space ice is common water ice laced with simple molecules. The team subsequently discovered amino acids, molecules present in, and essential for, life on Earth.

"This finding may shed light on the origin of life itself," said Dr. Max Bernstein, the first author and chemist at NASA Ames and the SETI Institute. "We found that amino acids can be made in the dense interstellar clouds where planetary systems and stars are made. Our experiments suggest that amino acids should be everywhere, wherever there are stars and planets."

The amino acids they detected (glycine, alanine and serine) are the basic parts of proteins from which all life is made. Proteins provide the structure for, and do all the work in, living things.

The amino acids produced in the NASA Ames lab are similar to those found previously in carbon-rich meteorites. Meteorites are pieces of asteroids or comets that have fallen to Earth. The chemical similarities may indicate that amino acids in meteorites were made in deep space, before the solar system formed, the scientists say.

"This finding suggests that Earth may have been seeded with amino acids from space in its earliest days," said Jason Dworkin of Ames and the SETI Institute. "And, since new stars and planets are formed within the same clouds in which new amino acids are being created, this increases the odds that life also evolved in places other than Earth."

"Taken in combination, these results suggest that interstellar chemistry may have played a significant part in supplying the Earth with some of the organic materials needed to jump-start life," Dworkin concluded.

To conduct their experiments, the research team simulated space-like conditions by freezing mixtures of molecules (such as wood alcohol and ammonia) that are abundant in interstellar clouds. They then exposed the resulting ice to ultraviolet light.

Previously, the team demonstrated that irradiating interstellar ice ‘look-alikes’ generated compounds called amphiphiles that can organize themselves to form membranes; and molecules called quinones that play important roles in the metabolism of all living organisms on Earth. The next step, they say, will be to tackle the issue of left- and right-handed amino acids. Both forms exist in space, but only the left-handed forms are used by life on Earth.

In addition to the principals, other scientists on the team included Drs. Louis Allamandola, George Cooper and Scott Sandford, all of Ames.Astrobiology is the multidisciplinary study of the origin, evolution, distribution and future of life in the universe. NASA Ames Research Center is the location of the central offices of the NASA Astrobiology Institute and serves as the agency’s lead center for astrobiology.

http://amesnews.arc.nasa.gov/releases/2002/02_33AR.html

Dan moet er een soort 'selectie' gebeurd zijn tussen linkse en rechtse geöriënteerde aminozuren, mogelijk op volgende wijze :

Possible Key Step In The Origin Of Life Identified

For a transition to occur from the pre-biological world of 4 billion years ago to the world we know today, amino acids--the building blocks of proteins in all living systems--had to link into chainlike molecules.
Now Robert Hazen and Timothy Filley of the Geophysical Laboratory of the Carnegie Institution of Washington, and Glenn Goodfriend of George Washington University have discovered what may be a key step in this process -- a step that has baffled researchers for more than a half a century.

Their work, supported by NASA's Astrobiology Institute and the Carnegie Institution, is reported in today's issue of the Proceedings of the National Academy of Sciences.

The molecular structure of all but one amino acid is an asymmetrical arrangement grouped around carbon. This arrangement means that there are two mirror-image forms of each amino acid; these forms are designated left-handed (L) and right-handed (D).

All of the chemistry of living systems is distinguished by its selective use of these (L) and (D), or chiral, molecules. Non-biological processes, on the other hand, do not usually distinguish between L and D variants.

For a transition to occur between the chemical and biological eras, some natural process had to separate and concentrate the left- and right-handed amino acids. This step, called chiral selection, is crucial to forming chainlike molecules of pure L amino acids.

Hazen and his collaborators performed a simple experiment. They immersed a fist-sized crystal of the common mineral calcite, which forms limestone and the hard parts of many sea animals, in a dilute solution of the amino acid aspartic acid and found that the left-and right-handed molecules adsorbed preferentially onto different faces of the calcite crystal.

Most minerals are centric, that is, their structures are not handed. However, some minerals display pairs of crystal surfaces that have a mirror relationship to each other. Calcite is one such mineral. It is common today, and was prevalent during the Archaean Era some 4 billion years ago when life first emerged.

This study suggests a plausible process by which the mixed D- and L-amino acids in the very dilute "primordial soup" could be both concentrated and selected on a readily-available mineral surface.

Hazen remarks, "Since the pioneering work of Stanley Miller in the 1950s, prebiotic synthesis of amino acids has been shown to be relatively easy. The real challenges now lie in selecting and concentrating L-amino acids, and then linking those molecules into chainlike proteins.

http://unisci.com/stories/20012/0501011.htm

Vandaar gaan we naar de autokatalyserende moleculen van de 'RNA-World'

An RNA Beginning?

All metabolism depends on enzymes and, until recently, every enzyme has turned out to be a protein. But proteins are synthesized from information encoded in DNA and translated into mRNA. So here is a chicken-and-egg dilemma. The synthesis of DNA and RNA requires proteins. So proteins cannot be made without nucleic acids and nucleic acids cannot be made without proteins.
The discovery that certain RNA molecules have enzymatic activity provides a possible solution. These RNA molecules - called ribozymes - incorporate both the features required of life:
- storage of information
- the ability to act as catalysts

While no ribozyme in nature has yet been found that can replicate itself, ribozymes have been synthesized in the laboratory that can catalyze the assembly of short oligonucleotides into exact complements of themselves. The ribozyme serves as both the template on which short lengths of RNA ("oligonucleotides" are assembled following the rules of base pairing and
the catalyst for covalently linking these oligonucleotides.

In principal, the minimal functions of life might have begun with RNA and only later did proteins take over the catalytic machinery of metabolism and DNA take over as the repository of the genetic code. Several other bits of evidence support this notion of an original "RNA world":

Many of the cofactors that play so many roles in life are based on ribose; for example:
- ATP
- NAD
- FAD
- coenzyme A
- cyclic AMP
- GTP

In the cell, all deoxyribonucleotides are synthesized from ribonucleotide precursors.

Many bacteria control the transcription and/or translation of certain genes with RNA molecules, not protein molecules.

http://users.rcn.com/jkimball.ma.ult...Synthesis.html

Enz. maar er blijft uiteraard nog heel veel uitgezocht te worden.

6 juli 2003, 21:16	#52
Darwin Banneling Geregistreerd: 14 augustus 2002 Berichten: 5.668	De aminozuren lijken in de ruimte synthetiseerd te worden en komen dan via meteoren en mereorieten op de planeten terecht. NASA SCIENTISTS CREATE AMINO ACIDS IN DEEP-SPACE-LIKE ENVIRONMENT NASA scientists today announced the creation of amino acids, critical for life, in an environment that mimics deep space. The research will be published in the March 28 issue of the journal Nature. In a laboratory at NASA Ames Research Center in California’s Silicon Valley, the team of astrobiologists shone ultraviolet light on deep-space-like "ices," simulating conditions that are commonplace in interstellar space. Deep-space ice is common water ice laced with simple molecules. The team subsequently discovered amino acids, molecules present in, and essential for, life on Earth. "This finding may shed light on the origin of life itself," said Dr. Max Bernstein, the first author and chemist at NASA Ames and the SETI Institute. "We found that amino acids can be made in the dense interstellar clouds where planetary systems and stars are made. Our experiments suggest that amino acids should be everywhere, wherever there are stars and planets." The amino acids they detected (glycine, alanine and serine) are the basic parts of proteins from which all life is made. Proteins provide the structure for, and do all the work in, living things. The amino acids produced in the NASA Ames lab are similar to those found previously in carbon-rich meteorites. Meteorites are pieces of asteroids or comets that have fallen to Earth. The chemical similarities may indicate that amino acids in meteorites were made in deep space, before the solar system formed, the scientists say. "This finding suggests that Earth may have been seeded with amino acids from space in its earliest days," said Jason Dworkin of Ames and the SETI Institute. "And, since new stars and planets are formed within the same clouds in which new amino acids are being created, this increases the odds that life also evolved in places other than Earth." "Taken in combination, these results suggest that interstellar chemistry may have played a significant part in supplying the Earth with some of the organic materials needed to jump-start life," Dworkin concluded. To conduct their experiments, the research team simulated space-like conditions by freezing mixtures of molecules (such as wood alcohol and ammonia) that are abundant in interstellar clouds. They then exposed the resulting ice to ultraviolet light. Previously, the team demonstrated that irradiating interstellar ice ‘look-alikes’ generated compounds called amphiphiles that can organize themselves to form membranes; and molecules called quinones that play important roles in the metabolism of all living organisms on Earth. The next step, they say, will be to tackle the issue of left- and right-handed amino acids. Both forms exist in space, but only the left-handed forms are used by life on Earth. In addition to the principals, other scientists on the team included Drs. Louis Allamandola, George Cooper and Scott Sandford, all of Ames.Astrobiology is the multidisciplinary study of the origin, evolution, distribution and future of life in the universe. NASA Ames Research Center is the location of the central offices of the NASA Astrobiology Institute and serves as the agency’s lead center for astrobiology. http://amesnews.arc.nasa.gov/releases/2002/02_33AR.html Dan moet er een soort 'selectie' gebeurd zijn tussen linkse en rechtse geöriënteerde aminozuren, mogelijk op volgende wijze : Possible Key Step In The Origin Of Life Identified For a transition to occur from the pre-biological world of 4 billion years ago to the world we know today, amino acids--the building blocks of proteins in all living systems--had to link into chainlike molecules. Now Robert Hazen and Timothy Filley of the Geophysical Laboratory of the Carnegie Institution of Washington, and Glenn Goodfriend of George Washington University have discovered what may be a key step in this process -- a step that has baffled researchers for more than a half a century. Their work, supported by NASA's Astrobiology Institute and the Carnegie Institution, is reported in today's issue of the Proceedings of the National Academy of Sciences. The molecular structure of all but one amino acid is an asymmetrical arrangement grouped around carbon. This arrangement means that there are two mirror-image forms of each amino acid; these forms are designated left-handed (L) and right-handed (D). All of the chemistry of living systems is distinguished by its selective use of these (L) and (D), or chiral, molecules. Non-biological processes, on the other hand, do not usually distinguish between L and D variants. For a transition to occur between the chemical and biological eras, some natural process had to separate and concentrate the left- and right-handed amino acids. This step, called chiral selection, is crucial to forming chainlike molecules of pure L amino acids. Hazen and his collaborators performed a simple experiment. They immersed a fist-sized crystal of the common mineral calcite, which forms limestone and the hard parts of many sea animals, in a dilute solution of the amino acid aspartic acid and found that the left-and right-handed molecules adsorbed preferentially onto different faces of the calcite crystal. Most minerals are centric, that is, their structures are not handed. However, some minerals display pairs of crystal surfaces that have a mirror relationship to each other. Calcite is one such mineral. It is common today, and was prevalent during the Archaean Era some 4 billion years ago when life first emerged. This study suggests a plausible process by which the mixed D- and L-amino acids in the very dilute "primordial soup" could be both concentrated and selected on a readily-available mineral surface. Hazen remarks, "Since the pioneering work of Stanley Miller in the 1950s, prebiotic synthesis of amino acids has been shown to be relatively easy. The real challenges now lie in selecting and concentrating L-amino acids, and then linking those molecules into chainlike proteins. http://unisci.com/stories/20012/0501011.htm Vandaar gaan we naar de autokatalyserende moleculen van de 'RNA-World' An RNA Beginning? All metabolism depends on enzymes and, until recently, every enzyme has turned out to be a protein. But proteins are synthesized from information encoded in DNA and translated into mRNA. So here is a chicken-and-egg dilemma. The synthesis of DNA and RNA requires proteins. So proteins cannot be made without nucleic acids and nucleic acids cannot be made without proteins. The discovery that certain RNA molecules have enzymatic activity provides a possible solution. These RNA molecules - called ribozymes - incorporate both the features required of life: - storage of information - the ability to act as catalysts While no ribozyme in nature has yet been found that can replicate itself, ribozymes have been synthesized in the laboratory that can catalyze the assembly of short oligonucleotides into exact complements of themselves. The ribozyme serves as both the template on which short lengths of RNA ("oligonucleotides" are assembled following the rules of base pairing and the catalyst for covalently linking these oligonucleotides. In principal, the minimal functions of life might have begun with RNA and only later did proteins take over the catalytic machinery of metabolism and DNA take over as the repository of the genetic code. Several other bits of evidence support this notion of an original "RNA world": Many of the cofactors that play so many roles in life are based on ribose; for example: - ATP - NAD - FAD - coenzyme A - cyclic AMP - GTP In the cell, all deoxyribonucleotides are synthesized from ribonucleotide precursors. Many bacteria control the transcription and/or translation of certain genes with RNA molecules, not protein molecules. http://users.rcn.com/jkimball.ma.ult...Synthesis.html Enz. maar er blijft uiteraard nog heel veel uitgezocht te worden.