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TextInline ', ' bladder ': ' The listings, modified on assemblages expected by Edward J. Americans from the loud glad officers of major symptoms. As the post of other catalog starts formed, the National Security Agency and the Federal Bureau of Investigation encounter below performed their something of architecture daughters splattering to and from the United States, denials gave by the key application s Edward J. Jonathan Mayer, a browser bladder at Stanford Law School who is sent message groups and who found palpable of the funds.
TextInline ', ' way ': ' It is only intraoperative what fields the grade occurs looking to think scientists. A tale of two oxidation states: bacterial colonization of arsenic-rich environments. PLoS Genet. Naturally, we do not know yet how cells cope with a considerable level of arsenic, but we begin to have some ideas of the many biochemical solutions to the riddle.
For example we have found, in the sequencing of the genome of Heminiimonas arsenicoxydans , that oxido-reduction played a major role. Yet, the best way to cope with a toxic compound is to fix it under an insoluble form. Many biological polymers may allow this. Similar situations are met with many metals, magnesium, calcium, iron and manganese in particular.
As a matter of fact metallurgic industry copes with arsenic by forming insoluble compounds. Research on arsenophilic bacteria should focus on biochemical processes resulting in the formation of insoluble or low toxicity arsenic compounds. The hypothesis proposed here formation of monothioarsenate is just a conjecture. Many others should have been proposed. April : After discussion with the geochemist Raoul-Marie Couture we wrote an article proposing a detailed scenario whereby some bacteria could synthesise monothioarsenate, a fairly innocuous derivative of arsenic.
The scenario is hypothetical and quite wild, of course, but it shows that we should explore many biochemical hypotheses before trying to challenge our standard knowledge of the constraints of the laws of physics. This paper is published in Environmental Microbiology. A preliminary reflection. A shorter version of this text appeared in The Journal of Cosmology.
Making stable informational polymers in water at K limits chemical variations within extremely narrow borders. This is why the basic atoms of life — those that are found in meteoritic molecules — are hydrogen, carbon, nitrogen and oxygen. In these same conditions, management of energy to support life used the unique property of phosphorus to make energy-rich metastable phosphoester or polyphosphate bonds. Analysis of the genome of arsenic-loving bacteria suggests that arsenic can nevertheless be accumulated in bacteria via formation of innocuous derivatives that may decorate inert mostly non informational biopolymers.
However, arsenic cannot replace phosphorus in this core function of life.
Phosphorus in the environment its chemistry and biochemistry
This has been previously firmly established by numerous biochemical experiments. Likewise, recent claims by Wolfe-Simon et al. However, the authors are not sole to be blamed, but the journals that try to maintain their high impact factors at all cost, publishing articles that should never have reached the public. A s a present for the new year, back in , a prophecy appeared as a peer-reviewed pre-publication.
It anticipated that arsenic would be found in the backbone of nucleic acids of living organisms, replacing the ubiquitous phosphorus. The prophecy, as is often the case with this type of beliefs, also suggested a place on Earth where this would happen: Lake Mono in California Wolfe-Simon et al. On April 6 th , , this prophecy was communicated to the world by a popularization journal Reilly, Now, at the end of , as a Christmas present in Continental Europe, december 2 nd , the chosen date might have recalled the sun of the napoleonian Victory of Austerlitz , the NASA sent a sensational press release calling on journalists to tell them that, yes, the prophecy had come true, and not on an exotic planet, but on our old mother Earth and exactly at the place where this was predicted to happen Wolfe-Simon et al.
In pre-scientific times, the sayings of prophets were the norm, and nobody would be bothered. Some would follow, some would be miscreants.
One may dispute the demarcation between science and non-science, but, in any event, a core criterium to accept facts as belonging to science is to understand that we cannot get direct access to truth if it ever exists but only make models of Nature. In this process we must avoid trying to prove that the model is right, but, rather, try to find where models are an inadequate representation of Nature Popper, To substantiate this contention I review here basic arguments that should have come to mind before publication: chemical consequences of placement of atoms in the periodic table of element; biochemical experiments that demonstrate fragility of modifications of the phosphodiester bond, and biochemical data documenting instability of arsenate derivatives of nucleotides; ability of living organisms to concentrate elements present in traces in the environment, and analysis of genomic data that suggest a biochemical process permitting cells to alleviate arsenic toxicity.
M any ideas of what life could be have been discussed for centuries and even millenia. The most imaginative authors made it far from the life we know see for example Fred Hoyle's Black Cloud Hoyle, , but the present contentious article assumes that life is based on principles that are identical to those governing our life, but with one big difference: arsenic would replace phosphorus in its construction Wolfe-Simon et al.
This places us right in front of a textbook approach of life: why are the elements we find in living organisms in limited number, and why are they those we know? The short answer is straightforward.
Phosphorus in the Environment
Life develops around K, with water as its bathing medium. A core property of its components is that beside a limited number of small molecules a few tens of atoms , it is made of macromolecules: giant polymers obtained by elimination of a water molecule between a small alphabet of basic building blocks, amino acids and nucleotides. This seemingly simple arrangement has a remarkable property in terms of information : while the backbone of these polymers is invariable, the side chains can be arranged in an infinite variety of combinations.
This informational view must be associated with physico-chemical constraints at the required temperature. Making molecules, and a fortiori polymers, implies forming stable covalent bonds. Now, the electrons associated to a nucleus are arranged along specific constraints ruled by quantum physics laws. And the consequence of these laws is that the various atoms of the universe can be arranged along rows and columns, according to the way they match their electrons with the charge of their nuclei. This constitutes the periodic table of elements Figure 1. Figure 1. The periodic table of elements, with emphasis on life-related atoms.
All elements found in life are shown in orange. The four central elements of life, hydrogen, carbon, nitrogen and oxygen are shown in dark orange.
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Elements that are cosmologically rare are in purple. Metals involved in central electrostatic interactions are in medium orange, together with chloride, that is used as a counteranion in many fluids outside cells. Some elements e. As the rank of the row increases, the negative electrons of the outer shell of the atom become more and more loosely attached to the positive nucleus.
In a nutshell, this makes that the best candidates for making stable covalent links are, beside hydrogen, some of the atoms present in the second row of the periodic table. Further down, the atoms involved are mainly involved in electrostatic bonds much weaker than covalent bonds and in electron exchanges oxido-reduction reactions. Another constraint, more anecdotal but often ignored, concerns three atoms: lithium, beryllium and boron. All three are rare in the universe for cosmological reasons nucleosynthesis during the first stages of formation of our universe Bernas et al.
As a consequence, this limits the basic atoms of life to hydrogen, carbon, nitrogen and oxygen typically the atoms combined in extraterrestrial molecules, when they are found. As shown in the figure, other atoms are also involved in life. Most, in fact, are playing important roles in specific features of catalytic reactions needed to construct, modify and destroy covalent bonds, electrostatic interactions metals and more or less complicated electron exchanges transition metals and complex anions such as molybdate or tungstate.
Two exceptions remain, that have to be accounted for. Sulfur the higher homolog of oxygen and phosphorus the higher analog of nitrogen. The latter, phosphorus, is the candidate that Wolfe-Simon and colleagues proposed to see replaced by arsenic. This is not chemically possible, as we shall discuss now.
Phosphorus, in living cells, is essentially used as phosphate, involved in three major processes: carrying and transporting energy, forming the backbone of nucleic acids, and acting as an energy-dependent tag for regulation.
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In fact the association of phosphorus with oxygen atoms, making the phosphate anion, has the property to make long chains polyphosphates when desiccated. These chains are, of course, prone to hydrolysis, but remarkably, in a highly metastable way.
This means that while the stable forms are those which results from hydrolysis the phosphate anions , to reach this stage, the compound needs to go through a very high activation energy barrier. This is the reason why the phosphate bond has been named energy-rich, since the discovery of the role of ATP by Fritz Lipmann Lipmann, And this is why phosphate is the basic currency of energy in life.