New Szostak protocell is closest approximation to origin of life and Darwinian evolution so far

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by Gert Korthof

Origin of life researcher and Nobel Prize winner Jack Szostak has made an important step towards creating a prebiotically plausible protocell (prebiotic implies that it did not originate from pre-existing forms of life, but its components could have self-assembled from raw materials available under physical and chemical conditions of the early earth). The protocell is a fatty acid vesicle, which is a simpler form of a cell membrane, in which RNA replication occurs autonomously without the help of enzymes. The results have been published in Science Nov 29 2013.

This is the first time that nonenzymatic RNA copying succeeded inside a fatty acid vesicle. The big obstacle has always been that magnesium ion Mg2+ was necessary for RNA copying, but two negative side-effects of high Mg2+ levels frustrated success. Firstly, high Mg2+ levels break down the simple, fatty acid membranes that probably surrounded the first living cells. Secondly, Mg2+ catalyses degradation of single-stranded RNA. After a long trial-and-error process, Szostak et al. discovered that citrate removes these two side-effects. Citrate efficiently protects fatty acid membranes from the disruptive effects of high Mg2+ ion concentrations, while both allowing RNA copying and protecting single-stranded RNA from Mg2+-catalyzed degradation.

KorthofFig2.jpg

An illustration of a protocell, composed of a fatty acid membrane encapsulating RNA ribozymes. © Exploring Life’s Origins.

It would be easier to run a self-replicating RNA system (RNA replicase) in the lab without a cell membrane because the membrane is a barrier for transportation of raw materials. But the membrane is important because chemicals can be kept at high concentrations inside the cell. They are not diluted. The protocell is a unit which is spatially separated from its environment. It also is the beginning of a unit with its own internal environment. Furthermore, a unit could behave differently from other such units. For example, one unit could be more stable than another. Or it could divide more efficiently than others. So it is a good idea that the system has a primitive membrane. More advantages of a membrane will appear later.

The protocell is called a ‘protocell’ because it is very much simpler than the modern eukaryotic cell, and even simpler than a bacterium.

It would also be easier to have enzymes available, but then one would need a system that could produce enzymes, and that would require DNA and complex transcription and translation machinery. That machinery would not be available in the RNA-world. However, RNA combines the properties of an enzyme and an information carrier (ribozymes).

Why are replication and cell division important in the origin of life? The effect of RNA replication and cell division is that it produces more of the same. These processes lower the probability of accidental destruction of the whole line of protocells.

It is clear that RNA replication would benefit from the presence of a suitable membrane. But what would be the benefit for the membrane to have RNA molecules inside itself? Self-replicating RNA on its own does not make a difference for the cell. The Science publication did not mention what benefit that could be. However, in a previous publication (Szostak, 2012) Szostak suggested that “catalyzed phospholipid synthesis could confer such a selective advantage by driving protocell membrane growth through the adsorption of fatty acid molecules from surrounding vesicles.” So, if those RNA molecules were present in the protocell, we would have a system in which the components stabilize each other. The protocell would stop being an accidental, unstable combination of components. The two components would reinforce each other’s formation.

A crucial advantage of a membrane now becomes clear: the copies of RNA molecules are kept in the same compartment. After a successful cell division each daughter cell would inherit approximately the same RNA molecules and other chemicals (RNA building blocks, Mg2+, citrate, fatty acids) that contributed to the success. Therefore, the protocell would become more frequent in the population based on inherited properties. In other words: nothing less than Darwinian evolution by natural selection.

A requirement for Darwinian evolution of the protocells is that the RNA makes copying mistakes (mutations) and that these make a difference in fitness. That is certainly an easy requirement, since copying would be sloppy at first anyway. The error-prone copying would be the basis of natural selection of RNA-carrying protocells. The protocells would have the ability to improve themselves. This could be the start of life and evolution.

A working version of a complete protocell has not yet been achieved in a laboratory setting. Other problems need to be solved, such as the fact that citrate is not a plausible prebiotic component: it needs to be replaced by an alternative component. Finally, at a certain level of complexity, a third main component of the cell would be helpful: chemical energy (metabolism). Nevertheless, conceptually and practically, the Szostak protocell is the closest approximation so far to the origin of life forms which have the potential to evolve.

Sources

33 Comments

Well this would certainly seem to lend some credence to the RNA world hypothesis. As for metabolism, perhaps a type of self replicating RNA could be found that could metabolize some simple sugar molecules. Or maybe a peptidyl transferase RNA could be found that could synthesize some proteins that could serve as enzymes. It would be a start.

Of course the resident trolls will be along any minute in order to spout nonsense about “intelligent design”. You don’t think so? Well how about the guy who thought that the formation of ice under a vent was evidence for a young earth, cause that’s just like stuff in caves don’t ya know! Anyway, life can’t be that complicated if even humans can reproduce it from scratch. Not so much intelligence needed after all it seems.

Wonderful! And it is for this reason I so assiduously follow PT and the scientists enabling amateurs, like myself, to keep up to date with brand new research.

I must pop over to UD in about 10 days time when they have had time to realise, recoil, and react; however poorly and incompetantly.

What is Szostak and his team’s next hurdle? Once RNA can replicate within the cell without degradation of the cell wall, what next? Laboratory mitosis? Or am I several steps beyond?

This comment has been moved to The Bathroom Wall.

DS said:

Of course the resident trolls will be along any minute in order to spout nonsense about “intelligent design”. You don’t think so? Well how about the guy who thought that the formation of ice under a vent was evidence for a young earth, cause that’s just like stuff in caves don’t ya know!

5 hours - 19 minutes from your post. Close enough. Booby strikes again.

Takes more than a fruit fly to spoil our ointment!

Creationists love this artificial life stuff. If you can’t create life, then it’s too complex to have arisen naturally. If you can create life, it obviously required some intelligence to do so. It’s the perfect heads they win, tails you lose scenario. At least they seem to think so. In actuality of course it merely demonstrates the feasibility of an abiotic origin for replicating systems.

Perhaps they are just worried about the potential applications of such a powerful new technology. After all, fear of death is their primary motivator in all things.

Do follow the link under the picture (above). There are some really cool animations there.

For those of use who don’t stare through a microscope each day, it’s hard to remember that these are not “static” structures, like our skin or bones or organs, or like static pictures on a page. These are instead fairly loosely (or at least dynamically) held individual molecules, that are always in random thermally generated Brownian motion. Once you see the parts of the assemblage all wiggling about, it becomes much more plausible to imagine them interacting in some fashion.

When all we see are static pictures or drawings, explaining how this large molecule fits like a key into this other large molecule, it becomes reasonable to ask, “Well, how did the cell know to grab molecule “A” and stick it to molecule “B”?”. With only the static drawings, it looks like a well defined key in an unchanging lock. Even simple animations often just show the static “key” molecule approaching the static “lock” molecule, in a well controlled manner, turning the lock, and then moving on. Even animations of the assembly or copying of DNA or RNA typically show precise, “intentional” motions of the molecules in question.

But, looking at animations like these, it becomes more clear that we’re talking about relatively flexible structures all wiggling about, all bumping into each other, in relatively rapid and random ways, and that, occasionally, two of those flexible structures will stick together in certain ways. Given the nature of those structures, two molecules are more likely to stick together in one way than in another.

Looked at another way, we (the lay public) tend to imagine these molecular parts acting as we see desecrate objects acting around us in our daily lives. We don’t have the personal experience of parts (molecules) where the environment (water) is on the same scale as we are, and where the interactive forces between molecules bumping into each other is on the same order of energy as the forces holding the parts together.

It’s like the difference between walking from one exhibit to another in a relatively sparsely populated museum, and trying to move from one side of a densely populated train platform to another, where you are literally check to jowl with all the other people all constantly bumping into each other.

Detailed, dynamic animations like these are wonderful teaching tools to better show what is really going on.

Very interesting. In the book What is Life?, Addy Pross brings up two areas of inquiry about the origin of life. One is on its historical origins, which is where we ask ‘where’ and ‘when’ and exactly ‘how’ did life get started. We know very few things about the historical origin of life since the earth has changed a lot since then, and the geological record has not preserved the earliest events. The other area of inquiry is about the a-historical origins of life. Here is where we ask ‘how could life get started in principle’. The a-historical line of inquiry has progressed most handsomely, so much so that it is hard to sort out all the different ways in which life could have begun in principle. Szostok and others have given us a lot to think about, and it is heartening to learn of yet more progress in this area.

Scott F said:

Detailed, dynamic animations like these are wonderful teaching tools to better show what is really going on.

This year’s Nobel Prize in Chemistry went to Martin Karplus, Michael Levitt, and Arieh Warshel for “the development of multiscale models for complex chemical systems.”

There is also a nice article about the development and history of this work on pages 13 to 16 of the December 2013 issue of Physics Today.

The work goes back to 1967 and well before. As anyone can discover by picking up a statistical mechanics or a quantum mechanics textbook, chemical bonds are not all equal. One can even learn about chemical bonds in a high school chemistry course.

In stark contrast to what these researchers have done – and from what one can learn from textbooks – the ID/creationists calculate the probability of a complex molecular assembly as 1/NL, where N is the number of choices of molecule for each position in a string of length L.

As any high school physics/chemistry student can recognize, the ID/creationist “calculation” doesn’t even take into account the temperature. The ID/creationist “calculation” is complete gibberish based on the ID/creationist notion that the second law of thermodynamics says everything comes all apart unless intelligence intervenes; therefore no abiogenesis or evolution.

I’m still waiting for a god to be observed doing anything like it.

Or anything at all, for that matter.

Glen Davidson

Mike Elzinga said:

The ID/creationist “calculation” is complete gibberish based on the ID/creationist notion that the second law of thermodynamics says everything comes all apart unless intelligence intervenes; therefore no abiogenesis or evolution.

As an illustration of exactly what ID/creationists are trying to do, take a look at Sal Cordova’s latest screed out of a set of ongoing attempts to poo-poo abiogenesis and evolution. The contrast between pretend scientist, Cordova, and real scientists cannot be more starkly illustrated.

Its still just a cell.

robert van bakel said:

Wonderful! And it is for this reason I so assiduously follow PT and the scientists enabling amateurs, like myself, to keep up to date with brand new research.

I must pop over to UD in about 10 days time when they have had time to realise, recoil, and react; however poorly and incompetantly.

What is Szostak and his team’s next hurdle? Once RNA can replicate within the cell without degradation of the cell wall, what next? Laboratory mitosis? Or am I several steps beyond?

More than “several” steps - mitosis is a complex process of DNA based chromosomes, involving exquisite cell cycle timing and multiple enzymes. (We all know that now a creationist will start crowing the old “if it’s complicated it must have been created by magic” routine because I said this, I’m going to say it anyway and note in advance that this creationist response will be silly.)

However, this research is extremely exciting, not least of all because it involves an effort to model early MEMBRANES.

Modern cells are surrounded by membranes, as well as, for some organisms, cell walls. Among other things, the ionic concentrations of the intracellular milieu are usually quite different from the ionic concentrations outside the cell (it may be “always” not “usually” but I’ve been indefinite in case there are exceptions I’m not aware of). This actually creates a small electrical potential across the cell membrane. Contractility, among other things, depends on this. The cellular membrane is a crucial part of modern life.

As an interested amateur, I’ve sometimes voiced the critique that some abiogenesis hypotheses focused excessively on nucleic acid replication, without any attention to the need for a membrane. So this research is very interesting.

DS said:

Creationists love this artificial life stuff. … If you can create life, it obviously required some intelligence to do so.

But what it doesn’t require is divinity.

They can wiggle all they want, but there’s a big difference between “creating life requires a couple of grad students and a good lab” and “creating life requires a unique, divine, being who has the power to whip up an entire universe”.

The article indicates that amino acid components can cross the simple fatty acid membranes that they are describing. They also note in passing that “modern” cell membranes (the phospholipids) are more complex. I know that modern cells have various “valves” (if you will) that open and close to let various elements in or out and to control internal chemical concentrations. However, even without those “valves”, are the “modern” membranes still permeable to various molecules? Or does their relative complexity make them less permeable than the simple membranes described?

Thank you ‘harold’, I’ll stay tuned.

Scott F said:

The article indicates that amino acid components can cross the simple fatty acid membranes that they are describing. They also note in passing that “modern” cell membranes (the phospholipids) are more complex. I know that modern cells have various “valves” (if you will) that open and close to let various elements in or out and to control internal chemical concentrations. However, even without those “valves”, are the “modern” membranes still permeable to various molecules? Or does their relative complexity make them less permeable than the simple membranes described?

Well, it’s often called a “semi-permeable membrane,” but is rather impermeable (or at least it happens too slowly) to a number of things, apart from the channels and gates (for many of those channels) that let larger molecules and ions get through. Fat/oil soluble materials tend to pass rather better than do many other substances, for the simple reason that the membranes are made of lipids. Water tends to get across (bacteria keep from taking in too much water in freshwater environments simply by the cell wall preventing the expansion that would have to occur to do that), mainly because there’s a lot of it about, but sometimes channels are needed to let more move across than would normally.

“Selectively permeable” is probably more correct for today’s cell membranes, while “semi-permeable” seems to fit the “leaky” early hypothesized membranes better than current membranes.

Glen Davidson

stevaroni said:

DS said:

Creationists love this artificial life stuff. … If you can create life, it obviously required some intelligence to do so.

But what it doesn’t require is divinity.

They can wiggle all they want, but there’s a big difference between “creating life requires a couple of grad students and a good lab” and “creating life requires a unique, divine, being who has the power to whip up an entire universe”.

I see this was answered well already, but just to emphasize something -

The selective permeability of modern cell membranes, and their ability to keep the intracellular compartment chemically quite different from the extracellular compartment, is critical for modern life. Cell theory is one of the other major underpinning theories of biomedical science. When we study what we call life, we are studying cells, or things like viruses, which require cells for their own replication.

Models of abiogenesis are at an exciting but very early stage.

harold said:

stevaroni said:

DS said:

Creationists love this artificial life stuff. … If you can create life, it obviously required some intelligence to do so.

But what it doesn’t require is divinity.

They can wiggle all they want, but there’s a big difference between “creating life requires a couple of grad students and a good lab” and “creating life requires a unique, divine, being who has the power to whip up an entire universe”.

I see this was answered well already, but just to emphasize something -

The selective permeability of modern cell membranes, and their ability to keep the intracellular compartment chemically quite different from the extracellular compartment, is critical for modern life. Cell theory is one of the other major underpinning theories of biomedical science. When we study what we call life, we are studying cells, or things like viruses, which require cells for their own replication.

Models of abiogenesis are at an exciting but very early stage.

Oops, that was a reply to Scott F.

DS said:

Creationists love this artificial life stuff. If you can’t create life, then it’s too complex to have arisen naturally. If you can create life, it obviously required some intelligence to do so. It’s the perfect heads they win, tails you lose scenario. At least they seem to think so. In actuality of course it merely demonstrates the feasibility of an abiotic origin for replicating systems.

Perhaps they are just worried about the potential applications of such a powerful new technology. After all, fear of death is their primary motivator in all things.

If life (or the vertebrate eye, or the human body, or whatever) is “too complex” to have been “designed” by the smartest “intelligent designers” that we know of, then how can someone claim that that is evidence that it is “intelligently designed”? This is only an example of the advocates of “intelligent design” not thinking through what they are saying.

But I don’t think that “fear of death” is the primary motivator. I’d suggest “embarrassment at being physically related to monkeys”. The embarrassment being all the deeper because it is so obvious that we are related.

And it gets them tangled up in all sorts of problems. Or, rather, it would get them tangled up if they were to reflect a bit on what they are claiming. Just as with “too complex to be designed, therefore it must be designed”; so, too, in order to try to avoid being like a monkey, they end up with “purposefully designed to be like a monkey” (rather than that merely being a natural consequence of common descent).

TomS said:

DS said:

Creationists love this artificial life stuff. If you can’t create life, then it’s too complex to have arisen naturally. If you can create life, it obviously required some intelligence to do so. It’s the perfect heads they win, tails you lose scenario. At least they seem to think so. In actuality of course it merely demonstrates the feasibility of an abiotic origin for replicating systems.

Perhaps they are just worried about the potential applications of such a powerful new technology. After all, fear of death is their primary motivator in all things.

If life (or the vertebrate eye, or the human body, or whatever) is “too complex” to have been “designed” by the smartest “intelligent designers” that we know of, then how can someone claim that that is evidence that it is “intelligently designed”? This is only an example of the advocates of “intelligent design” not thinking through what they are saying.

But I don’t think that “fear of death” is the primary motivator. I’d suggest “embarrassment at being physically related to monkeys”. The embarrassment being all the deeper because it is so obvious that we are related.

And it gets them tangled up in all sorts of problems. Or, rather, it would get them tangled up if they were to reflect a bit on what they are claiming. Just as with “too complex to be designed, therefore it must be designed”; so, too, in order to try to avoid being like a monkey, they end up with “purposefully designed to be like a monkey” (rather than that merely being a natural consequence of common descent).

The right wing social/political ideology includes numerous ideas which are not considered acceptable to express, except secretly or anonymously, even by right wingers themselves.

Even the least controversial economic ideas aren’t quite openly expressed. For example, proposals to cut food stamps are usually made in language that implies that food stamps are the cause of the need for food stamps. “Such and such a number of people are on food stamps, this is bad, therefore we must cut food stamps”. The fact that some people will go hungry as a consequence is simply never expressed. The number of people who say “I know some people will go hungry but I don’t care” is very small. The number who actually feel this way but prefer to argue as if “cutting food stamps” is the same as “reducing the need for food stamps” is much greater. And this is one of the least controversial areas of right wing ideology.

Some ideas were highly acceptable to express in the recent past, but have become much less so - for example, homophobia and certain types of sexism.

Other ideas are implicitly endorsed, yet are simultaneously so taboo that they are denied even while being tacitly endorsed. Numerous right wing preferences, from really overt racism to the idea that we should be cavalier about dropping nuclear weapons on other countries, fit in this category.

Therefore, those who support this ideology have no choice but to communicate with coded language, often analogized as being similar to a dog whistle. Ideally, all the dogs start barking in approval, but no-one else quite understands what was said.

There are, of course, the John Derbyshires of the world, who rather overtly make statements that, say, Paul Ryan or even Dick Cheney would be inhibited to make, and who try to promote acceptance of scientific reality combined with blunt advocacy of harsh, racist, sexist authoritarian right wing politics.

Most post-modern authoritarian racist right wingers don’t want to do that. For whatever reason, they do NOT want the confrontation that would generate. They desperately prefer coded language. John Derbyshire is an eccentric, not well accepted by any group.

The major mechanism of coded language is to use rigid, movement-endorsed propaganda slogans, on less inflammatory topics, like creationist talking points. Everyone gets it. If you parrot creationist talking points and/or euphemistic right wing economic slogans, everyone understands perfectly well how you feel about more controversial issues surrounding race, gender, orientation, social welfare, international behavior, etc. But you didn’t say any of that more inflammatory stuff out loud, so you aren’t confronted for it.

I am not saying that this is a deliberate, conscious attempt to deceive. It is a contorted behavior provoked by a combination of fear, anger, widespread post-modern narcissistic self-absorption, total lack of self-awareness, confusion, shame, etc.

However, this MUST be understood to understand why creationists behave the way they do. The creationism is tied to a vast array of deeply ingrained misery-making yet superficially self-serving biases. To stop denying evolution is to question the whole thing. To give up evolution denial is to utterly change self-image, group identity, etc.

That’s a profound and, I think, accurate analysis, harold.

I suppose I could add that I believe that this group identity is actually what is driving creationism itself. I’m on a youtube thread - by the way, have you noticed that youtube has in effect increased the wordage limit on comments? - from the Pen and Teller “Bullshit” series, on creationism. It’s clear that the creationists there are completely incapable of telling fact from fiction, but also that the distinction doesn’t matter a jot to them. This isn’t about what is fact. It’s about who belongs to what group. Fascinating, and horrifying.

Anatole France said that it is his reasonable conversation which most frightens us in a madman.

John Derbyshire wrote Prime Obsession, the best book I’ve read about the Riemann hypothesis. It’s only the tiniest bit racist.

Dave Luckett said:

That’s a profound and, I think, accurate analysis, harold.

I suppose I could add that I believe that this group identity is actually what is driving creationism itself. I’m on a youtube thread - by the way, have you noticed that youtube has in effect increased the wordage limit on comments? - from the Pen and Teller “Bullshit” series, on creationism. It’s clear that the creationists there are completely incapable of telling fact from fiction, but also that the distinction doesn’t matter a jot to them. This isn’t about what is fact. It’s about who belongs to what group. Fascinating, and horrifying.

It is weirdly fascinating how it all is about the common enemy: science/evolution, and the corresponding big tent attitude. Facts are irrelevant when you are up against the greatest evil conceivable.

“A working version of a complete protocell has not yet been achieved in a laboratory setting. Other problems need to be solved, such as the fact that citrate is not a plausible prebiotic component: it needs to be replaced by an alternative component. Finally, at a certain level of complexity, a third main component of the cell would be helpful: chemical energy (metabolism). Nevertheless, conceptually and practically, the Szostak protocell is the closest approximation so far to the origin of life forms which have the potential to evolve”.

If these cells are to survive they have to be in a right environment and no substance added that would stop the process from developing (-and also to have an orange tree near by- : ). This protocell is unable to replicate without RNA. With the membrane and with RNA it can become pure and individual; otherwise it would be -iggelty pickelty-. I wonder what forms could come from the protocells development. It can only become what the elements allow, if it wants to have eyes it has to pick the right direction for that to happen unless that is all that is available to progress then it has no choice but to go that way. So the membrane is important to contain all the right ingredients to become what it’s going to be. I think it’s deeper than natural selection. I think it’s no choice but to become what the elements in the cell provide.

Just more vitalism nonsense and all mere assertion with completely no evidence.

Why do people think they can just ignore all of the discoveries in the past two hundred years and stick with outdated nonsense as if it had not been disproven already?

Marilyn said:

“A working version of a complete protocell has not yet been achieved in a laboratory setting. Other problems need to be solved, such as the fact that citrate is not a plausible prebiotic component: it needs to be replaced by an alternative component. Finally, at a certain level of complexity, a third main component of the cell would be helpful: chemical energy (metabolism). Nevertheless, conceptually and practically, the Szostak protocell is the closest approximation so far to the origin of life forms which have the potential to evolve”.

If these cells are to survive they have to be in a right environment and no substance added that would stop the process from developing (-and also to have an orange tree near by- : ). This protocell is unable to replicate without RNA. With the membrane and with RNA it can become pure and individual; otherwise it would be -iggelty pickelty-. I wonder what forms could come from the protocells development. It can only become what the elements allow, if it wants to have eyes it has to pick the right direction for that to happen unless that is all that is available to progress then it has no choice but to go that way. So the membrane is important to contain all the right ingredients to become what it’s going to be. I think it’s deeper than natural selection. I think it’s no choice but to become what the elements in the cell provide.

Since we don’t have time machines, we can’t go back in time to see how cellular life originated. The best we can do is model the process. This type of research is at a very early stage. The model discussed here is not intended to be perfectly complete. It’s a starting point, with some very intriguing features.

It’s something of an accident that we tend to think of RNA and DNA as the key to understanding the origin of life since you can make a pretty good case for metabolism or membranes as the critical factor. Oparin and Haldane, who were pioneers in abiogenesis research, emphasized the role of compartmentalization in life—c.f., Oparin’s coacervates; and Joseph Needham, who was an important biologist before he became more famous for his Science and Civilization in China project, thought that membranes were the central feature of life. It does seem to be true that the cell membrane is seldom if ever created de novo: all membranes from membranes seems as true as all cells from cells.

Think about the Maxwell’s demon meme: everybody focuses on the intelligence of the demon in allowing only high-energy particles to pass from one compartment to the other; but the demon would be out of luck if there weren’t a partition in the first place.

Jim said:

It’s something of an accident that we tend to think of RNA and DNA as the key to understanding the origin of life since you can make a pretty good case for metabolism or membranes as the critical factor. Oparin and Haldane, who were pioneers in abiogenesis research, emphasized the role of compartmentalization in life—c.f., Oparin’s coacervates; and Joseph Needham, who was an important biologist before he became more famous for his Science and Civilization in China project, thought that membranes were the central feature of life. It does seem to be true that the cell membrane is seldom if ever created de novo: all membranes from membranes seems as true as all cells from cells.

Think about the Maxwell’s demon meme: everybody focuses on the intelligence of the demon in allowing only high-energy particles to pass from one compartment to the other; but the demon would be out of luck if there weren’t a partition in the first place.

That’s an excellent point.

What we have in living cells now is roughly membrane-enclosed compartments of proteinaceous solution, with very different ionic composition from the extracellular environment, within which there are also nucleic acids. Nucleic acids are the key to replication, but the compartment replicates itself in parallel with them, so that when replication happens, the new nucleic acid sequences have an more or less identical highly specialized compartment of their own.

Nucleic acid sequences determine which proteins can be expressed, but signals from the extracellular and intracellular environment, ultimately, often at the end of long, redundant cascades, determine which amino acid sequences are transcribed or translated. It’s a feedback loop with no obvious “first” step.

However, there are also “lipid first” models. http://en.wikipedia.org/wiki/Gard_model

But a model of just nucleic acids replicating in solution isn’t terribly useful, even if it’s RNA that’s replicating. We all already know that RNA (or DNA) can form polymers and probably do a bit of self-replication in solution. We all already know that you can play with things like temperature and ions to affect that. It’s adding in the things like where membranes came from, where the relationship between nucleic acid sequences and protein sequences came from, where tRNA came from, etc, that will make models of abiogenesis especially interesting. Of course, just saying that doesn’t make it easy.

harold said:

Jim said:

It’s something of an accident that we tend to think of RNA and DNA as the key to understanding the origin of life since you can make a pretty good case for metabolism or membranes as the critical factor. Oparin and Haldane, who were pioneers in abiogenesis research, emphasized the role of compartmentalization in life—c.f., Oparin’s coacervates; and Joseph Needham, who was an important biologist before he became more famous for his Science and Civilization in China project, thought that membranes were the central feature of life. It does seem to be true that the cell membrane is seldom if ever created de novo: all membranes from membranes seems as true as all cells from cells.

Think about the Maxwell’s demon meme: everybody focuses on the intelligence of the demon in allowing only high-energy particles to pass from one compartment to the other; but the demon would be out of luck if there weren’t a partition in the first place.

That’s an excellent point.

What we have in living cells now is roughly membrane-enclosed compartments of proteinaceous solution, with very different ionic composition from the extracellular environment, within which there are also nucleic acids. Nucleic acids are the key to replication, but the compartment replicates itself in parallel with them, so that when replication happens, the new nucleic acid sequences have an more or less identical highly specialized compartment of their own.

Nucleic acid sequences determine which proteins can be expressed, but signals from the extracellular and intracellular environment, ultimately, often at the end of long, redundant cascades, determine which amino acid sequences are transcribed or translated. It’s a feedback loop with no obvious “first” step.

However, there are also “lipid first” models. http://en.wikipedia.org/wiki/Gard_model

But a model of just nucleic acids replicating in solution isn’t terribly useful, even if it’s RNA that’s replicating. We all already know that RNA (or DNA) can form polymers and probably do a bit of self-replication in solution. We all already know that you can play with things like temperature and ions to affect that. It’s adding in the things like where membranes came from, where the relationship between nucleic acid sequences and protein sequences came from, where tRNA came from, etc, that will make models of abiogenesis especially interesting. Of course, just saying that doesn’t make it easy.

My understanding, from brief past correspondence with Szostak, is that this is precisely what he’s working toward, even if he doesn’t live long enough to reach that stage himself. He’s seeking to establish not only that protocells of this sort can be bootstrapped from prebiotic chemistry without the involvement of an imaginary magic man, but that once thus bootstrapped, they can acquire these later features simply through the usual variation/selection process. As you say, we’re some way from that yet, but at least scientists such as Szostak are applying themselves diligently to the task, and putting in the research labour to answer the questions. Creationists would have us simply not bother, and simply accept blind mythological assertions as the “answer” for everything.

Give me “I don’t know the answer, but I’ll roll up my sleeves and do the experiments to find out” over “shut up and conform to doctrine” any day.

Scott F said:

… we see desecrate objects acting around us in our daily lives. …

You and I might, but those blessed by the Light of the Lamb (insert your choice of religio non-sequiturs here), by the power of their sheer presence, have mostly sacred objects around them, which act in much more divine ways.

That’s why only True Christians™ can do Real ScienceⓇ.

I am curious if we know of an abiotic source of citrate that seems to be necessary for this idea?

From the article: “The protocell is a fatty acid vesicle, which is a simpler form of a cell membrane, in which RNA replication occurs autonomously without the help of enzymes.”

This is a gross exaggeration of what Szostak achieved, as he would be the first to admit. RNA replication was not achieved without enzymes. What was achieved was RNA primer extension. It would be legitimate to also use the term ‘RNA Synthesis’. RNA replication clearly implies that you have a working system that will repeatedly make new RNA strands from a template. At least two template directed synthesis steps are required to reproduce one copy of the original, the bare minimum to legitimately be called replication.

This is the kind of exaggeration that both sides participate in to sway the argument. This is not splitting hairs, and from the comments on the message board it is clear that this exaggeration had the intended effect of making it seem like this protocell has a working nonenzymatic RNA replication system going in it.

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This page contains a single entry by Matt Young published on December 13, 2013 5:14 PM.

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