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Swift
2015-Mar-02, 03:44 PM
From R&D magazine (http://www.rdmag.com/news/2015/03/life-not-we-know-it-possible-saturns-moon-titan?et_cid=4440917&et_rid=54636800&location=top)


A new type of methane-based, oxygen-free life form that can metabolize and reproduce similar to life on Earth has been modeled by a team of Cornell Univ. researchers.

Taking a simultaneously imaginative and rigidly scientific view, chemical engineers and astronomers offer a template for life that could thrive in a harsh, cold world—specifically Titan, the giant moon of Saturn. A planetary body awash with seas not of water, but of liquid methane, Titan could harbor methane-based, oxygen-free cells.

Their theorized cell membrane, composed of small organic nitrogen compounds and capable of functioning in liquid methane temperatures of 292 degrees below zero, is published in Science Advances. The work is led by chemical molecular dynamics expert Paulette Clancy and first author James Stevenson, a graduate student in chemical engineering. The paper's co-author is Jonathan Lunine, director for Cornell's Center for Radiophysics and Space Research.

Lunine is an expert on Saturn's moons and an interdisciplinary scientist on the Cassini-Huygens mission that discovered methane-ethane seas on Titan. Intrigued by the possibilities of methane-based life on Titan, and armed with a grant from the Templeton Foundation to study non-aqueous life, Lunine sought assistance about a year ago from Cornell faculty with expertise in chemical modeling. Clancy, who had never met Lunine, offered to help.


Here is the article from Science Advances (http://advances.sciencemag.org/content/1/1/e1400067)

It looks like what they modeled was the membrane, not the entire organism. There doesn't appear to be any model for either a metabolic process or a genetic system.

Hypmotoad
2015-Mar-03, 05:45 AM
The documentary that I watched alluded to a lifeform we may have already detected before each commercial as a teaser. Finally they said that due to the detection of some signatory gas, I think they said methane, that bacterium as large as a dog might be fat and happy snorkeling through the lakes of Titan

Idk though, would be sweet to find such.

Noclevername
2015-Mar-03, 05:47 AM
The documentary that I watched alluded to a lifeform we may have already detected before each commercial as a teaser. Finally they said that due to the detection of some signatory gas, I think they said methane, that bacterium as large as a dog might be fat and happy snorkeling through the lakes of Titan

Idk though, would be sweet to find such.
It would, though detecting methane on Titan is like finding stink on a skunk. Titan literally has oceans of it.

Hypmotoad
2015-Mar-03, 06:35 AM
I would love to argue that it was amounts of gas detected and where but I can't because I really don't know. Was a good tease though and anything that sets me thinking about other things than which bill can I stall on this payday is a good thing.

Where is your sense of wonder, NCN? Why not a dog sized prokaryote, eh?

Skunks only stink sometimes in response to threat, other than that, they are great pets and are awesome in preventing women from having their way with me!

Noclevername
2015-Mar-03, 08:43 AM
Idk though, would be sweet to find such.


It would,


Where is your sense of wonder, NCN?

If agreeing that it would be an amazing find isn't wonder enough for you, what is ?

marsbug
2015-Mar-03, 05:37 PM
From R&D magazine (http://www.rdmag.com/news/2015/03/life-not-we-know-it-possible-saturns-moon-titan?et_cid=4440917&et_rid=54636800&location=top)



Here is the article from Science Advances (http://advances.sciencemag.org/content/1/1/e1400067)

It looks like what they modeled was the membrane, not the entire organism. There doesn't appear to be any model for either a metabolic process or a genetic system.

To me this looks like a model of the equivilent of the kind of protocells that form when lipid molecules from meteorites are mixed in water (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2890201/). EDIT: Lab made protocells (called lipid vesicles) of a similar kind..... end edit .... do show many life like qualities, the grow by taking up nutrients, they replicate (http://www.ncbi.nlm.nih.gov/pubmed/17425354), they can maintain homeostasis to an extent. They are not generally regarded as being alive, but are seen as being an important step on the road (http://www.nature.com/nchem/journal/v3/n10/abs/nchem.1127.html) from chemistry to life, so a titan viable equivilent is still very exciting.

Fiery Phoenix
2015-Mar-04, 02:12 AM
What does methane-based even mean, really? As in relies on methane as a replacement source for water/oxygen? Also, wouldn't such a lifeform be considered carbon-based owing to the fact that methane contains carbon?

Exciting news nonetheless. Always been fascinated by Titan and the potential behind it.

Noclevername
2015-Mar-04, 02:29 AM
What does methane-based even mean, really? As in relies on methane as a replacement source for water/oxygen? Also, wouldn't such a lifeform be considered carbon-based owing to the fact that methane contains carbon?

Exciting news nonetheless. Always been fascinated by Titan and the potential behind it.

It means using liquid methane as a solvent, just as water is the solvent for our biochemistry. And such life would be technically carbon based, but at such low temperatures it would have to use a different set of organic molecules to work with.

Colin Robinson
2015-Mar-04, 09:14 AM
From R&D magazine (http://www.rdmag.com/news/2015/03/life-not-we-know-it-possible-saturns-moon-titan?et_cid=4440917&et_rid=54636800&location=top)



Here is the article from Science Advances (http://advances.sciencemag.org/content/1/1/e1400067)

It looks like what they modeled was the membrane, not the entire organism. There doesn't appear to be any model for either a metabolic process or a genetic system.

Thank you for calling attention to this exciting work. Yes, it is clear that their model is about a composition for a cell membrane that could be viable in Titan conditions. Regarding metabolism on Titan, thermodynamically viable inputs and outputs have been identified, but not (as far as I know) a specific pathway from the inputs to the outputs. Regarding a genetic system, S.A.Benner suggested (http://www.lpi.usra.edu/meetings/abscicon2010/pdf/5097.pdf) that a polyether could do this job. However, NASA people found (https://astrobiology.nasa.gov/nai/reports/annual-reports/2013/jpl-titan/task-351-titan-as-a-prebiotic-chemical-system/) that polyethers are not sufficiently soluble in liquid methane.

Conceivably Titan may turn out to have concentrations of organic molecules enclosed in membranes, with catalysts breaking stuff down and building stuff up, and the whole system catalysing copies of itself (thus reproducing) but without a genetic system comparable to DNA... Not sure whether we humans would classify that as life or not, but either way it might help us understand a little more about the relation between life and non-life in the universe, and the path from one to the other.

Colin Robinson
2015-Mar-04, 09:28 AM
I would love to argue that it was amounts of gas detected and where but I can't because I really don't know.

Things that suggest the possibility of life of Titan include acetylene levels, ethane levels and hydrogen levels. These three substances are all present, but in lower amounts that expected (based on what was known of Titan's atmosphere). They are all known to be generated from methane and solar energy in the upper atmosphere, so the question is why they haven't built up more? A possible answer is that they're getting decomposed (with release of energy) as fast as they are being generated. That is exactly what microbes are good at doing — decomposing stuff, and getting energy out of it... But there could conceivably be a process of chemical "decay" occurring without microbes.


Where is your sense of wonder, NCN? Why not a dog sized prokaryote, eh?

If life is found on Titan, dog-sized or not, it will be a tremendous breakthrough.

marsbug
2015-Mar-04, 11:03 PM
I try hard to be conservative about such things, but... I'm going to go out on a limb and admit I think the potential for complex chemistry and complex structures, the presence of chemical energy sources, and the presence of liquid solvants to mediate and concentrate things will have allowed something with life like properties to arise, if not something undeniably alive (albeit in a very alien way). But that's a personal opinion, not an evidence backed conclusion (although it is inspired by the evidence to had wrt Titans environment).

If I'm wroing then that's also very interesting!

Colin Robinson
2015-Mar-05, 09:07 AM
I try hard to be conservative about such things, but... I'm going to go out on a limb and admit I think the potential for complex chemistry and complex structures, the presence of chemical energy sources, and the presence of liquid solvants to mediate and concentrate things will have allowed something with life like properties to arise, if not something undeniably alive (albeit in a very alien way). But that's a personal opinion, not an evidence backed conclusion (although it is inspired by the evidence to had wrt Titans environment).

If I'm wroing then that's also very interesting!

My personal opinion is similar to yours. However, we won't actually know until a robot lander designed for an extended mission is sent to Titan.

The modelling of possible compositions of cell membranes doesn't prove that cells or even membranes actually exist there. However, it does strengthen the case that the next lander should have a microscope to look for structures, as well as devices such mass spectrometers to study chemical composition.

malaidas
2015-Mar-05, 11:35 AM
Thank you for calling attention to this exciting work. Yes, it is clear that their model is about a composition for a cell membrane that could be viable in Titan conditions. Regarding metabolism on Titan, thermodynamically viable inputs and outputs have been identified, but not (as far as I know) a specific pathway from the inputs to the outputs. Regarding a genetic system, S.A.Benner suggested (http://www.lpi.usra.edu/meetings/abscicon2010/pdf/5097.pdf) that a polyether could do this job. However, NASA people found (https://astrobiology.nasa.gov/nai/reports/annual-reports/2013/jpl-titan/task-351-titan-as-a-prebiotic-chemical-system/) that polyethers are not sufficiently soluble in liquid methane.

Conceivably Titan may turn out to have concentrations of organic molecules enclosed in membranes, with catalysts breaking stuff down and building stuff up, and the whole system catalysing copies of itself (thus reproducing) but without a genetic system comparable to DNA... Not sure whether we humans would classify that as life or not, but either way it might help us understand a little more about the relation between life and non-life in the universe, and the path from one to the other.

The point of what classifies as life is being argued elsewhere, but basically what classes as life depends upon how you want to see it. The original MRS GREN, which is widely still held, has no requirement for DNA though, only that is performs all of the functions within the acronym. Sure this throws up problems when considering the likes of viruses though, hence viruses are sometimes designated as quasi lifeforms.

swampyankee
2015-Mar-05, 05:16 PM
I think one of the objections being raised against life on TItan, or life using liquids other than water as a solvent, was that a cell membrane was impossible.

Since the study seems to show that a cell membrane is possible while using methane as a solvent, this objection is likely void. Finding life is still non-trivial. Since we've found life in all sorts of unlikely places, like micro-fractures in rocks 10 km below the surface, we may be able to find Titan life if we can ever get there.

Titan would be a great place to explore: we could use aircraft (buoyantly or dynamically supported), boats, amphibious vehicles, etc. There would be some clever design required, but it would not require the type of development that getting something to Europa's sub-surface oceans would demand.

Colin Robinson
2015-Mar-09, 08:08 PM
To me this looks like a model of the equivilent of the kind of protocells that form when lipid molecules from meteorites are mixed in water (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2890201/). These do show many life like qualities, the grow by taking up nutrients, they replicate (http://www.ncbi.nlm.nih.gov/pubmed/17425354), they can maintain homeostasis to an extent. They are not generally regarded as being alive, but are seen as being an important step on the road (http://www.nature.com/nchem/journal/v3/n10/abs/nchem.1127.html) from chemistry to life, so a titan viable equivilent is still very exciting.

Is it really possible to get a protocell which takes up nutrients, maintains homeostasis and replicates by simply taking lipid molecules from meteorites and mixing them with water?

I followed the three links you've given, but I cannot see where they substantiate what you've said.

marsbug
2015-Mar-09, 10:23 PM
Well I'm 99% sure the papers I've linked show that lipid vesicles can do all those things, but it's 10pm here so I'll wait to re-read them until a bit later in the week. I'm also 99% sure that at least 1 of the papers states that such vesicles have been formed by material from the murchison meteorite being mixed in water. I vaugely recall the material was heated either before introduction to the water or once in solution I'll re-read the material when I get a chance. I don't think the vesicles formed from the murchison material were shown to do the things lipid vesicles whipped up in the lab will do, and I'm sorry if that wasn't clear - now I re-read my post I can see I could have worded it better.

publiusr
2015-Mar-14, 08:32 PM
Well if we can't find one, maybe we can make one and set it to use on Titan.

Colin Robinson
2015-Mar-15, 04:51 AM
Well I'm 99% sure the papers I've linked show that lipid vesicles can do all those things, but it's 10pm here so I'll wait to re-read them until a bit later in the week. I'm also 99% sure that at least 1 of the papers states that such vesicles have been formed by material from the murchison meteorite being mixed in water. I vaugely recall the material was heated either before introduction to the water or once in solution I'll re-read the material when I get a chance. I don't think the vesicles formed from the murchison material were shown to do the things lipid vesicles whipped up in the lab will do, and I'm sorry if that wasn't clear - now I re-read my post I can see I could have worded it better.

There are theoretical models of protocells (https://en.wikipedia.org/wiki/Protocell) consisting of various sorts of lipids, water and not much else which are still able to grow, reproduce and evolve. The Lipid World hypothesis posits that such protocells happened earlier than protein-based metabolism or nucleic acid genes.

To what extent has this process been duplicated in laboratories? I know there have been experiments on the way various sorts of lipids can self-organise in water into structures such as liposomes, and interact with other organic compounds. But I am not aware that a fully functioning lipid protocell has actually been synthesised yet.

Short description of a recent experiment (http://pandasthumb.org/archives/2013/12/new-szostak-pro.html) with lipid membranes, magnesium ion, citrate and RNA.The RNA makes copies of itself inside the vesicle without help of enzymes; but that doesn't mean the system as a whole can reproduce itself. It is exciting, but it isn't yet a fully functioning protobiont.

marsbug
2015-Mar-15, 10:40 PM
Firstly apologies for taking my sweet time replying, real life is pressing down hard at the moment.

I've been quite unclear here, and we're veering off topic towards another mobius loop 'what is life' argument. I've used the term protocell, and this seems to have been taken to mean a fully functioning but simple life form, which is not how I meant it. I'll stick to the term vesicle from now on.

I'm not putting forwards that anything like a fully functional cell can be made by simply adding fatty acids to water. However a DNA less vesicle that grows and self reproduces? It seems fairly clear to my non specialist eye, from a very brief googling, that a lot of papers in the field....

Autopoietic reproduction of fatty acid vesicles (http://pubs.acs.org/doi/abs/10.1021/ja00105a004)


"Conditions are described under which vesicles made of caprylic a acid and oleic acid in water are able to undergo autopoiec reproduction...."

Achievements and open questions in the self-reproduction of vesicles and synthetic minimal cells (http://pubs.rsc.org/en/content/articlelanding/2010/cc/b913997d#!divAbstract)


"Supramolecular chemistry was enriched, about twenty years ago, by the discovery of the self-reproduction of micelles and vesicles. The dynamic aspects and complexity of these systems makes them good models for biological compartments......."

A Novel System of Self-Reproducing Giant Vesicles (http://pubs.acs.org/doi/abs/10.1021/ja029379a)

Building artificial cells and protocell models: Experimental approaches with lipid vesicles


"Lipid vesicles are often used as compartment structures for preparing cell-like systems and models of protocells, the hypothetical precursor structures of the first cells at the origin of life. Although the various artificially made vesicle systems are already remarkably complex, they are still very different from and much simpler than any known living cell. Nevertheless, the preparation and study of the structure and the dynamics of functionalized vesicle systems may contribute to a better understanding of biological cells, in particular of the essential features of a living cell that are not found in the non-living form of matter. ..."

...regard it as widely accepted that lipid vesicles can grow by absorbing lipid molecules in the environment around them, and will reproduce under the right conditions, and will keep a different set of internal conditions than their environment, although ONLY as there is a physical barrier between the inside and outside of the vesicle - in my opinion that isn't homeostasis, I'm happy to admit I remembered wrong there.

Note, I havn't mentioned DNA or RNA. No idea where that comes in, except that it would have to for us to have a true cell instead of a vesicle, in order to provide a means of inheritable information. However it seems to me, from the little bit of reading I've done, that lipid vesicles are widely regarded as being capable of growth and reproduction under the right conditions - namely those they are put under in a lab to make them grow and reproduce, and so provide useful models for protocells.

I could be totally wrong, and misinterpreting, as this is definately not my field.

Let's say I am. The point I originally wished to make, generally, is that many systems are capable of some of the behavoirs of a living system (crystals in supersaturated solution, simple self replicating molecules (http://news.discovery.com/tech/biotechnology/scientists-buil-self-replicating-molecule-111014.htm), or even hurricanes for example). To have a few life like qualities is not a special acolade these days, although it was once thought to be special.

However some such systems are thought to represent a step along the road of chemical progression from life to non life. It is (in my opinion only) concievable that the nitrogen based 'cell membrane' mentioned in the OP might be one such system, but representing a potential step along the road to liquid methane cryo-life. And, incidentally, by the by, it's not significant in any meaningful way, the grAphic of the methanogenic membrane looks a bit like some of the images I've seen of lipid vesicles too. Which is, pretty obviously, the only real link between lipid vesicles and this, unless the nitrogen based 'cell membrane' proves to have similar properties to vesicles at some point.

Colin Robinson
2015-Mar-16, 01:50 AM
Firstly apologies for taking my sweet time replying, real life is pressing down hard at the moment.

I've been quite unclear here, and we're veering off topic towards another mobius loop 'what is life' argument. I've used the term protocell, and this seems to have been taken to mean a fully functioning but simple life form, which is not how I meant it. I'll stick to the term vesicle from now on.

I'm not putting forwards that anything like a fully functional cell can be made by simply adding fatty acids to water. However a DNA less vesicle that grows and self reproduces? It seems fairly clear to my non specialist eye, from a very brief googling, that a lot of papers in the field....

Autopoietic reproduction of fatty acid vesicles (http://pubs.acs.org/doi/abs/10.1021/ja00105a004)


Achievements and open questions in the self-reproduction of vesicles and synthetic minimal cells (http://pubs.rsc.org/en/content/articlelanding/2010/cc/b913997d#!divAbstract)



A Novel System of Self-Reproducing Giant Vesicles (http://pubs.acs.org/doi/abs/10.1021/ja029379a)

Building artificial cells and protocell models: Experimental approaches with lipid vesicles


...regard it as widely accepted that lipid vesicles can grow by absorbing lipid molecules in the environment around them, and will reproduce under the right conditions, and will keep a different set of internal conditions than their environment, although ONLY as there is a physical barrier between the inside and outside of the vesicle - in my opinion that isn't homeostasis, I'm happy to admit I remembered wrong there.

Note, I havn't mentioned DNA or RNA. No idea where that comes in, except that it would have to for us to have a true cell instead of a vesicle, in order to provide a means of inheritable information. However it seems to me, from the little bit of reading I've done, that lipid vesicles are widely regarded as being capable of growth and reproduction under the right conditions - namely those they are put under in a lab to make them grow and reproduce, and so provide useful models for protocells.

Thank you very much for the links. (The "Building artificial cells..." link didn't work for me, but I found the paper by googling its title.) Looking at the material you've mentioned, I agree that it's been established that lipid vesicles with quite simple composition can not only grow but also reproduce in suitable conditions.


I could be totally wrong, and misinterpreting, as this is definately not my field.

I don't have specialist knowledge in this field either, but I feel pretty sure that you're not misinterpreting.


The point I originally wished to make, generally, is that many systems are capable of some of the behavoirs of a living system (crystals in supersaturated solution, simple self replicating molecules (http://news.discovery.com/tech/biotechnology/scientists-buil-self-replicating-molecule-111014.htm), or even hurricanes for example). To have a few life like qualities is not a special acolade these days, although it was once thought to be special.

I agree that something can have a few life-like qualities without actually being a living thing...

This also suggests that the emergence of life on a planet is a gradual process, rather than the lucky moment some have supposed. The much-used term "chemical evolution" is not quite right either, because if membrane formation was one of the earliest steps, then the process was one of emerging structures not only of emerging molecules (chemical compounds).


However some such systems are thought to represent a step along the road of chemical progression from life to non life. It is (in my opinion only) concievable that the nitrogen based 'cell membrane' mentioned in the OP might be one such system, but representing a potential step along the road to liquid methane cryo-life. And, incidentally, by the by, it's not significant in any meaningful way, the grAphic of the methanogenic membrane looks a bit like some of the images I've seen of lipid vesicles too.

I think the similarity is because in both cases there is a hollow ball of molecules, and in both cases the molecules are imaged as clusters of smaller balls (atoms).


Which is, pretty obviously, the only real link between lipid vesicles and this, unless the nitrogen based 'cell membrane' proves to have similar properties to vesicles at some point.

Stevenson, Lunine and Clancy, who did the computer modelling mentioned in the OP, are saying that nitrogen-containing acrylonitrile membranes would have similar properties (in Titan conditions), to lipid membranes (in Earth conditions), in at least two respects: stability and flexibility.

Colin Robinson
2015-Mar-16, 03:49 AM
Some time ago I looked at a paper about Titan which used the term "sterile nitriles" — described as compounds formed in absence of water and oxygen, which are not in themselves biologically interesting. I've just googled and re-found this paper at

A surface science paradigm for a post-Huygens Titan Mission (http://hdl.handle.net/2014/41760)

It turns out that one of the authors is none other than Jonathan Lunine — co-author of the recent paper about biological possibilities of acrylonitriles, which are a subnet of the nitriles. It is an interesting change of mind.

Eclogite
2015-Mar-16, 07:20 AM
This also suggests that the emergence of life on a planet is a gradual process, rather than the lucky moment some have supposed. I shall concede that Darwin expressed something close to such a view in his letter to Joseph Hooker (the warm little pond), but I doubt that any researcher engaged in abiogenesis research today thinks a single, simple step from life to non-life is reality.

Colin Robinson
2015-Mar-16, 11:28 AM
I shall concede that Darwin expressed something close to such a view in his letter to Joseph Hooker (the warm little pond), but I doubt that any researcher engaged in abiogenesis research today thinks a single, simple step from life to non-life is reality.

Later than Darwin, though now almost half a century ago, the French biochemist Jacques Monod wrote (in a book called Chance and Necessity): "The universe was not pregnant with life nor the biosphere with man. Our number came up in the Monte Carlo game." ...

I agree that a lot of recent modelling about abiogenesis suggests that Monod was wrong. However it is still conceivable that the emergence of life on Earth involved a step whose prior probability was so low that life in any form is extremely rare in the universe. (Or perhaps a couple of steps whose combined probability was so low...)

That scenario will cease to be conceivable if exotic microbial life is found on Titan. We will then know that the universe actually was and is (metaphorically speaking) "pregnant with life", although not necessarily with human-like life...

Eclogite
2015-Mar-16, 03:49 PM
You have reminded me that I need to get a copy of Monod's book.

Monod, a Nobel prize winner declares that life will be incredibly rare, perhaps unique to Earth. At the other end of the spectrum of opinion, Christian de Duve, a Nobel prize winner, declares that life is inevitable and common. I'm not a Nobel prize winner, so perhaps am not even entitled to an opinion, but I view any assessment of the likelihood of life is presumptuous when working with a sample size of one.

That said, I don't think Monod was claiming that we won everything in a single spin of the roulette wheel. I believe he and most (all) current researchers think it took several spins of the wheel to get to what we would call life. The debate is over whether we were betting on red, or 23, 18, 22, 4, 31, etc in that order.

swampyankee
2015-Mar-16, 08:56 PM
You have reminded me that I need to get a copy of Monod's book.

Monod, a Nobel prize winner declares that life will be incredibly rare, perhaps unique to Earth. At the other end of the spectrum of opinion, Christian de Duve, a Nobel prize winner, declares that life is inevitable and common. I'm not a Nobel prize winner, so perhaps am not even entitled to an opinion, but I view any assessment of the likelihood of life is presumptuous when working with a sample size of one.

That said, I don't think Monod was claiming that we won everything in a single spin of the roulette wheel. I believe he and most (all) current researchers think it took several spins of the wheel to get to what we would call life. The debate is over whether we were betting on red, or 23, 18, 22, 4, 31, etc in that order.


Of course you're entitled to an opinion; it's intuitively obvious to the most casual of observers that nobody has a clue about the existence of life off Earth. Right now, the Nobel laureates are demonstrating that they're willing to speculate with minimal data.

Colin Robinson
2015-Mar-16, 10:07 PM
You have reminded me that I need to get a copy of Monod's book.

Monod, a Nobel prize winner declares that life will be incredibly rare, perhaps unique to Earth. At the other end of the spectrum of opinion, Christian de Duve, a Nobel prize winner, declares that life is inevitable and common. I'm not a Nobel prize winner, so perhaps am not even entitled to an opinion, but I view any assessment of the likelihood of life is presumptuous when working with a sample size of one.

That said, I don't think Monod was claiming that we won everything in a single spin of the roulette wheel. I believe he and most (all) current researchers think it took several spins of the wheel to get to what we would call life. The debate is over whether we were betting on red, or 23, 18, 22, 4, 31, etc in that order.

The finding mentioned in the OP — that acrylonitriles in liquid methane could form membranous structures like those formed by lipids in liquid water — seems consistent with the idea that there are many winning combinations for life.

marsbug
2015-Mar-16, 11:58 PM
Of course you're entitled to an opinion; it's intuitively obvious to the most casual of observers that nobody has a clue about the existence of life off Earth. Right now, the Nobel laureates are demonstrating that they're willing to speculate with minikal data.

... plus speculating on minimal data can be a lot more fun than having to actually back your ideas up with evidence. It's a favorite passtime in the pub my university lecturers frequented :D :D :D

swampyankee
2015-Mar-17, 02:40 AM
... plus speculating on minimal data can be a lot more fun than having to actually back your ideas up with evidence. It's a favorite passtime in the pub my university lecturers frequented :D :D :D

Some fraction of that speculation results in useful ideas for research.

Eclogite
2015-Mar-17, 10:18 AM
Of course you're entitled to an opinion; Well, yes. I was just pretending to be humble.


it's intuitively obvious to the most casual of observers that nobody has a clue about the existence of life off Earth. If only this were true. Across the spectrum, from forums such as this, to paper's published in the top research journals*, we see claims for this, or that probability of life. I agree with you that we cannot, currently, do more than speculate - and a lot of speculation is idle speculation.

I think we shall, eventually, be able to define with some precision the steps by which life arose and assign quite tight probabilities to each, as well as identifying alternative routes that could have delivered the same functional result. I think we are still several decades away and will not see that in my lifetime. (Of course, I'm not 100% confident I'll see another Wimbledon in my lifetime. :))


Right now, the Nobel laureates are demonstrating that they're willing to speculate with minimal data.I am quite comfortable with that, as long as we say "if these assumptions are true this will follow", rather than "I think these are good assumptions and this follows from them".

Colin Robinson
2015-Mar-18, 12:38 AM
Some fraction of that speculation results in useful ideas for research.

Yes. There is a relation between speculation and experiment, which is summed up in Karl Popper's phrase "conjectures and refutations". Making educated guesses and developing ways to test them is an important part of scientific method.

Colin Robinson
2015-May-25, 11:30 PM
One way of looking at this "azotosome" model.

Over the last few decades, organic molecules — often called "building blocks of life" — have been found in quite a few places beyond Earth, such as meteors and interstellar clouds. What we haven't yet found, is a place beyond Earth where such "building blocks" have assembled themselves into a microbe-sized "wall".

Now we have a computer model suggesting that in Titan conditions, molecules of acetonitrile may indeed self-assemble into membranes. Whether or not the reality on Titan matches the model remains to be seen — there could be some other factor there that prevents membrane formation. However, if we do find such micro "walls" on Titan, it will be a scientific breakthrough, even if they turn out NOT to be part of a functioning "house" or "workshop".

marsbug
2015-Jun-23, 02:35 PM
Firstly apologies for taking my sweet time replying, real life is pressing down hard at the moment.

I've been quite unclear here, and we're veering off topic towards another mobius loop 'what is life' argument. I've used the term protocell, and this seems to have been taken to mean a fully functioning but simple life form, which is not how I meant it. I'll stick to the term vesicle from now on.

I'm not putting forwards that anything like a fully functional cell can be made by simply adding fatty acids to water. However a DNA less vesicle that grows and self reproduces? It seems fairly clear to my non specialist eye, from a very brief googling, that a lot of papers in the field....

Autopoietic reproduction of fatty acid vesicles (http://pubs.acs.org/doi/abs/10.1021/ja00105a004)


Achievements and open questions in the self-reproduction of vesicles and synthetic minimal cells (http://pubs.rsc.org/en/content/articlelanding/2010/cc/b913997d#!divAbstract)



A Novel System of Self-Reproducing Giant Vesicles (http://pubs.acs.org/doi/abs/10.1021/ja029379a)

Building artificial cells and protocell models: Experimental approaches with lipid vesicles


...regard it as widely accepted that lipid vesicles can grow by absorbing lipid molecules in the environment around them, and will reproduce under the right conditions, and will keep a different set of internal conditions than their environment, although ONLY as there is a physical barrier between the inside and outside of the vesicle - in my opinion that isn't homeostasis, I'm happy to admit I remembered wrong there.

Note, I havn't mentioned DNA or RNA. No idea where that comes in, except that it would have to for us to have a true cell instead of a vesicle, in order to provide a means of inheritable information. However it seems to me, from the little bit of reading I've done, that lipid vesicles are widely regarded as being capable of growth and reproduction under the right conditions - namely those they are put under in a lab to make them grow and reproduce, and so provide useful models for protocells.

I could be totally wrong, and misinterpreting, as this is definately not my field.

Let's say I am. The point I originally wished to make, generally, is that many systems are capable of some of the behavoirs of a living system (crystals in supersaturated solution, simple self replicating molecules (http://news.discovery.com/tech/biotechnology/scientists-buil-self-replicating-molecule-111014.htm), or even hurricanes for example). To have a few life like qualities is not a special acolade these days, although it was once thought to be special.

However some such systems are thought to represent a step along the road of chemical progression from life to non life. It is (in my opinion only) concievable that the nitrogen based 'cell membrane' mentioned in the OP might be one such system, but representing a potential step along the road to liquid methane cryo-life. And, incidentally, by the by, it's not significant in any meaningful way, the grAphic of the methanogenic membrane looks a bit like some of the images I've seen of lipid vesicles too. Which is, pretty obviously, the only real link between lipid vesicles and this, unless the nitrogen based 'cell membrane' proves to have similar properties to vesicles at some point.

Sorry for the thread necromancy, but now I can add to the above this: http://ucsdnews.ucsd.edu/pressrelease/scientists_create_synthetic_membranes_that_grow_li ke_living_cells

Quote from the materials:


“The membranes we created, though completely synthetic, mimic several features of more complex living organisms, such as the ability to adapt their composition in response to environmental cues,” said Neal Devaraj, an assistant professor of chemistry and biochemistry at UC San Diego who headed the research team, which included scientists from the campus’ BioCircuits Institute.

“Many other scientists have exploited the ability of lipids to self-assemble into bilayer vesicles with properties reminiscent of cellular membranes, but until now no one has been able to mimic nature’s ability to support persistent phospholipid membrane formation,”

Colin Robinson
2015-Jun-24, 11:37 PM
Sorry for the thread necromancy, but now I can add to the above this: http://ucsdnews.ucsd.edu/pressrelease/scientists_create_synthetic_membranes_that_grow_li ke_living_cells

Quote from the materials:

A synthetic lipid membrane that grows continually by means of a single autocatalyst... Very interesting experiment!

marsbug
2015-Jul-27, 02:51 PM
I'm thread necromacny-ing again, but I've got question that I hope someone on the forum might be able to help me wih: the azatosome model works (as far as I understand it) because of the attraction of the polar heads of the acrylonitrile molecules, immersed in the non-polar methane. I've been reading about the putative nitrogen geysers of Triton, and wondred, would this work in liquid N2, or in any non-polar cryogenic solvent? I can't think why not but my chemistry isn't up to answering this myself.

Colin Robinson
2016-Feb-21, 07:09 AM
I'm thread necromacny-ing again, but I've got question that I hope someone on the forum might be able to help me wih: the azatosome model works (as far as I understand it) because of the attraction of the polar heads of the acrylonitrile molecules, immersed in the non-polar methane. I've been reading about the putative nitrogen geysers of Triton, and wondred, would this work in liquid N2, or in any non-polar cryogenic solvent? I can't think why not but my chemistry isn't up to answering this myself.

Just found this interesting question. I don't think you can count on a different solvent at a different temperature working the same way, even if both solvents are non-polar. The British astrobiologist William Bains has done some lab work to find out what liquid nitrogen can and can't dissolve. He established that one group of compounds it can dissolve are polysilanols, which are the silicon equivalent of sugars. There is a non-technical account (http://www.williambains.co.uk/astrobiology/life2.html) of this on his website. Don't know whether or not he or anyone else has tested how liquid nitrogen interacts with acrylonitrile.