What other elements could the molecules of life systems be based on?

[raeleen]

Hi everyone! First time poster!

 

I am an undergraduate student studying molecular biology. I am certain you have all heard NASA's recent announcement wherein they discovered lifeforms which can utilize arsenic in lieu of phosphorous as a fundamental component of their genome.

 

I've always wondered what possible elements life systems can consist of, and when I say life systems, I don't just mean the ones that exist on earth, but POTENTIAL life systems anywhere in the cosmos.

 

I have never felt that life is limited to the compounds of us earth-based creatures, and that somewhere out there, elsewhere in the universe, are creatures with a TOTALLY UNIQUE biochemistry which looks nothing like the earth-based lifeforms we are familiar with.

 

NASA has proven that life is not limited to the compounds that we're familiar with. What other possible combinations of elements could be involved in life systems???

[Greippi]

Silicon, as opposed to carbon. However, this is unfeasible on our planet as it takes too much energy to make double/triple bonds between silicon atoms - which are pretty much essential for metabolism. Also, it can't make bonds with as diverse a range of atoms as carbon can. There are other reasons too.

 

Chlorine could also hypothetically be used instead of oxygen.

Edited December 4, 2010 by Greippi

[CharonY]

What I have to add is that the bacterium did not have a totally altered phsyiology per se. It is just able to withstand enormous concentrations of As and incorporate it into its chemistry and still survive that. I have only skimmed the paper but from the data it appeared to me that they generally just measured the proportion of P to As (and P was not 0), indirectly suggesting a gradual replacement, rather than full utilization of As. However, I would to find a quiet minute to read it more thoroughly.

[Moontanman]

If the truth be told the presence of a bacterium that uses arsenic isn't exactly unique. Other organisms, bacteria, algae and fungus use arsenic is various ways in their metabolisms instead of phosphorus.

 

http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry

 

Arsenic as an alternative to phosphorus

 

Arsenic, which is chemically similar to phosphorus, while poisonous for most Earth life, is incorporated into the biochemistry of some organisms.[10] Some marine algae incorporate arsenic into complex organic molecules such as arsenosugars and arsenobetaines. Fungi and bacteria can produce volatile methylated arsenic compounds. Arsenate reduction and arsenite oxidation have been observed in microbes (Chrysiogenes arsenatis).[11] Additionally, some prokaryotes can use arsenate as a terminal electron acceptor during anaerobic growth and some can utilize arsenite as an electron donor to generate energy.

 

It has been speculated that the earliest life on Earth may have used arsenic in place of phosphorus in the backbone of its DNA.[12] A common objection to this scenario is that arsenate esters are so much less stable to hydrolysis than corresponding phosphate esters that arsenic would not be suitable for this function.[13] However, a geomicrobiology study released by NASA has revealed that a bacterium named GFAJ-1, collected in the sediments of Mono Lake in eastern California, appears to employ such 'arsenic DNA' when cultured without phosphorus.[14][15][16][17][18] The bacterium may employ high levels of poly-β-hydroxybutyrate to stabilize its arsenate esters.[16]

 

 

Other exotic element-based biochemistries

 

Boron's chemistry is possibly even more variable than that of carbon, since it has the ability to form polyhedral clusters and three-center two-electron bonds. Boranes are dangerously explosive in Earth's atmosphere, but would be more stable in a reducing environment. However, boron's low cosmic abundance makes it less likely as a base for life than carbon.

Various metals, together with oxygen, can form very complex and thermally stable structures rivaling those of organic compounds; the heteropoly acids are one such family. Some metal oxides are also similar to carbon in their ability to form both nanotube structures and diamond-like crystals (such as cubic zirconia). Titanium, aluminum, magnesium and iron are all more abundant in the Earth's crust than carbon. Metal oxide-based life could therefore be a possibility under certain conditions, including those (such as high temperatures) at which carbon-based life would be unlikely.

Sulfur is also able to form long-chain molecules, but suffers from the same high reactivity problems as phosphorus and silanes. The biological use of sulfur as an alternative to carbon is purely theoretical, especially since sulfur usually forms only linear chains rather than branched ones. (The biological use of sulfur as an electron acceptor is widespread and can be traced back 3.5 billion years on Earth, thus predating the use of molecular oxygen.[9] Sulfur-reducing bacteria can utilize elemental sulfur instead of oxygen, reducing sulfur to hydrogen sulfide.)

 

More on boron life.

 

http://www.daviddarling.info/encyclopedia/B/boron-based_life.html

 

Boron is one of the few elements that seems to offer a plausible alternative to carbon as a basis for life elsewhere in the universe. Like carbon and silicon, boron has a strong tendency to form covalent molecular compounds. Being a group III element, however, it has one less valence electron than the number of valence orbitals, which makes its chemistry noticeably different from that of carbon.

 

There are no direct analogs to hydrocarbons in boron chemistry because, although boron forms a lot of different structural varieties of hydride, in these the boron atoms are linked indirectly through hydrogen bridges. Boron forms bonds with nitrogen that are somewhat like the carbon-carbon bond two electrons from the nitrogen being donated in addition to the covalent electron sharing. Boron-nitrogen compounds largely match the chemical and physical properties of alkanes (such as methane and ethane) and aromatic hydrocarbons (such as benzene) but with higher melting and boiling points. Borazole especially is both chemically and physically similar to benzene. However, the fact that borazole and its derivatives are more reactive than their benzene counterparts would make any boron-based biochemistry more feasible within the lower temperatures at which ammonia is a liquid solvent since the reactions would then be more controllable. Interestingly, boron has an affinity ammonia as a solvent, which would suit a low-temperature biological scheme.

 

One of the biggest drawbacks to boron as a basis for life it is scarcity. On Earth, its abundance in the continental crust is only about 10 parts per million, so that any biology would seem to depend on their being present some mechanism for bringing about greater local concentrations of the element.

 

Then there are the clouds...

 

http://www.npr.org/blogs/krulwich/2010/12/03/131783352/arsenic-life-is-nice-living-clouds-are-nicer

Edited December 5, 2010 by Moontanman

[raeleen]

If the truth be told the presence of a bacterium that uses arsenic isn't exactly unique. Other organisms, bacteria, algae and fungus use arsenic is various ways in their metabolisms instead of phosphorus.

 

 

Yes but in this case the arsenic is in their nucleotides and a unit of heredity! That's far more significant than incorporating arsenic into your metabolism.

 

My professor discussed the potential of silicon based life but said it was unlikely for the reasons already given and because carbon is so prevalent in the universe.

 

I REALLY wonder, I don't know about astronomy much, but when they are looking for plants that potentially harbor life, although we could never check except by going, if they are being too specific. I have always wondered if life on Earth is remotely similar to life on other planets. Does evolution converge upon the elements that we are made out of? Does it converge on quadrupeds as land-goers? Does it converge on humanoids as the sentient species? Or is Earth just a fluke?

Very interesting questions, at least to me

[Moontanman]

Yes but in this case the arsenic is in their nucleotides and a unit of heredity! That's far more significant than incorporating arsenic into your metabolism.

 

My professor discussed the potential of silicon based life but said it was unlikely for the reasons already given and because carbon is so prevalent in the universe.

 

I REALLY wonder, I don't know about astronomy much, but when they are looking for plants that potentially harbor life, although we could never check except by going, if they are being too specific. I have always wondered if life on Earth is remotely similar to life on other planets. Does evolution converge upon the elements that we are made out of? Does it converge on quadrupeds as land-goers? Does it converge on humanoids as the sentient species? Or is Earth just a fluke?

Very interesting questions, at least to me

 

 

Have you ever read "Wonderful Life"? http://en.wikipedia.org/wiki/Wonderful_Life_(book)

[steevey]

A very very weird one I heard was using xenon tetra-fluoride, because when fluorine de-attaches from xenon, that process is exothermic, and the fluorine can easily re-attach to the xenon in an endothermic process. It's a bit like how plants use ATP for photosynthesis. One end of the ADP forms, and with some energy carried from the sun by cells, becomes ATP. Then when the plant cells want to do something, the end of ATP de-attaches and releases that energy again.

Edited December 8, 2010 by steevey

[CharonY]

Before we go off into too much speculations check this out My link. I still have not found the time to read the paper in more detail, but she picks out and elaborates a few things that I have noticed by skimming, as well as things that I have missed.

[steevey]

Before we go off into too much speculations check this out My link. I still have not found the time to read the paper in more detail, but she picks out and elaborates a few things that I have noticed by skimming, as well as things that I have missed.

 

It does increase the chances for places life can exist, but can't I take almost any element that makes up our DNA and replace it with another element in the same group? It might not be as efficient, but if those were the only materials for life to evolve around, I bet life could use any other group element.

Edited December 14, 2010 by steevey

[Greippi]

Yes but in this case the arsenic is in their nucleotides and a unit of heredity! That's far more significant than incorporating arsenic into your metabolism.

 

 

The proof for incorporation of arsenic into nucleotides/proteins etc is not very convincing in this study.

[pioneer]

The most abundant molecules in the universe are H2 and H2O. That just so happens to be the energy range limit for life on earth; food/energy (<H2) and a final product (H2O). It would make sense that life would become part of that universal energy economy.

 

In the diagram below one can see H, O, C, Fe, N, Mg, Ca, etc as being way up there in abundance. It is not coincidental that chlorophyl and hemoglobin use central atoms taken the top ten of the universe. Life is simply an extension of the universe. P or phosphorus is a bit down the line, with As or arsenic even further down the line. These may not be as critical for exchanging, although the abundance of P compared to As would make it more likely.

 

[raeleen]

The proof for incorporation of arsenic into nucleotides/proteins etc is not very convincing in this study.

 

I can't see what is wrong right off the bat. Can you please quote what you think isn't convincing in the study so we can talk about it?

 

So is Silicon the only other life element that people think could possibly exist?

[steevey]

The most abundant molecules in the universe are H2 and H2O. That just so happens to be the energy range limit for life on earth; food/energy (<H2) and a final product (H2O). It would make sense that life would become part of that universal energy economy.

 

In the diagram below one can see H, O, C, Fe, N, Mg, Ca, etc as being way up there in abundance. It is not coincidental that chlorophyl and hemoglobin use central atoms taken the top ten of the universe. Life is simply an extension of the universe. P or phosphorus is a bit down the line, with As or arsenic even further down the line. These may not be as critical for exchanging, although the abundance of P compared to As would make it more likely.

 

 

Of course its not accidental. Heavier elements are more complex and take more time for stars to reach a point to where those elements can be formed, so it only makes complete perfect sense anyway. But what increases the possibility for life like us, is what appears to be a pattern of elements lower in a group being able to replace elements higher in the a group.

 

It would be like the reverse of fluorine replacing chlorine, except the cause of it would be just a lack if fluorine, so life would just have to use what it has, whether its the most efficient or not. Because as you get into heavier elements, there's also less energy released from bonds, and on top of that, the charge from the nucleus becomes weaker as the required distance from the nucleus increases as you add more electrons.

Edited December 15, 2010 by steevey

[Greippi]

The first thing that jumped out at me was this:

The DNA purification doesn't look too rigorous. I'm not convinced the arsenic found isn't contamination. If you're going to come to conclusions as groundbreaking as this, the experimental procedure has to be extremely rigorous.

 

But I've discussed it with a number of other people and we've picked so many more holes in the research.

[CharonY]

As mentioned elsewhere, the paper mostly demonstrated high resilience of an organism to As, rather than living off it.

[mississippichem]

The first thing that jumped out at me was this:

The DNA purification doesn't look too rigorous. I'm not convinced the arsenic found isn't contamination. If you're going to come to conclusions as groundbreaking as this, the experimental procedure has to be extremely rigorous.

 

But I've discussed it with a number of other people and we've picked so many more holes in the research.

 

I agree. I would like to see [ce] ^{75}As[/ce] NMR of the proposed anomalous DNA before I can believe that phosphate has been replaced by arsenate. The As-O and As=O bonds are too easily hydrolyzed which makes me hesitant to buy this one.

[granpa]

Hi everyone! First time poster!

 

I am an undergraduate student studying molecular biology. I am certain you have all heard NASA's recent announcement wherein they discovered lifeforms which can utilize arsenic in lieu of phosphorous as a fundamental component of their genome.

 

I've always wondered what possible elements life systems can consist of, and when I say life systems, I don't just mean the ones that exist on earth, but POTENTIAL life systems anywhere in the cosmos.

 

I have never felt that life is limited to the compounds of us earth-based creatures, and that somewhere out there, elsewhere in the universe, are creatures with a TOTALLY UNIQUE biochemistry which looks nothing like the earth-based lifeforms we are familiar with.

 

NASA has proven that life is not limited to the compounds that we're familiar with. What other possible combinations of elements could be involved in life systems???

http://en.wikipedia.org/wiki/PAH_world_hypothesis

[CharonY]

If they gave me some samples I could run it through the MS for a few bucks.

[alpha2cen]

If they gave me some samples I could run it through the MS for a few bucks.

 

It might be a good paper to search for similar DNA structure organisms.

Doing the experiment again is also very good paper, too.

If these kind organisms were not existence in the Earth, it could be big problem.

That kind of difference is the same as the difference between virus and monkey.

DNA duplication, transcription, translation ,... every step should be changed.

And we have to rewrite bacteria evolutions. Its not related to prokaryotes, eukaryotes or archaea.

Biochemical difference is very very big.

Edited December 23, 2010 by alpha2cen