Rosa Lichtenstein
8th March 2011, 17:09
From the latest New Scientist:
Primordial Pac-Man: Oil droplet hints at life's origin
02 March 2011 by Michael Marshall
Simple oil drops show that if you get the conditions right, basic life may emerge almost fully formed
WHEN Stanley Miller and Harold Urey created amino acids by shooting sparks through a "primordial atmosphere" of methane, ammonia, hydrogen and water, biologists thought a full understanding of the origins of life was within reach. Almost 60 years on from the most famous origin-of-life experiment of them all, we're still waiting.
Could that be because biologists have been looking at the wrong part of the experiment? A fresh look at the tarry residue left behind in a Miller-Urey-style experiment has revealed something remarkable: when injected into a simple oil droplet, the gunk endows it with spookily lifelike behaviour - although crucially it cannot yet reproduce. Like Pac-Man, an oil droplet doped with tarry junk can sense and respond to its neighbours and move towards "food" sources.
Although the Miller-Urey set-up is best known for producing amino acids, its primary product is a complex hydrogen cyanide polymer that looks like black tar and has mostly been ignored. "For the most part, people filtered it off and threw it down the drain," says Bob Minard of Pennsylvania State University in University Park.
Martin Hanczyc at the University of Southern Denmark in Odense and his colleagues are being less dismissive. They previously showed that oil droplets doped with oleic anhydride have attributes generally associated with life, and now say that the overlooked gunk can imbue oil with the same properties.
Hanczyc spent four years experimenting with simple oil droplets. His earliest studies involved lacing drops of oily nitrobenzene with oleic anhydride before floating them in an alkaline aqueous solution. Immediately, the droplets began to jerk about, and moments later they shot off in straight lines.
Each droplet is powered by a simple chemical process. Oleic anhydride at the surface reacts with the surrounding water to create oleic acid, a surfactant that lowers the droplet's surface tension. By chance, the reaction is fastest at one point on the droplet's surface. As a result, this reactive hotspot draws oleic anhydride from within the droplet, setting up internal convection currents.
Meanwhile, the oleic acid skims across the droplet's surface to gather on the opposite side, setting up a pH gradient. This, along with the internal convection currents, is enough to force the droplet forwards through the aqueous solution (Journal of the American Chemical Society, vol 129, p 9386). Hanczyc compares the reactions happening in the hotspot to a metabolism, where fuel is broken down to produce the energy that drives the droplet forward.
Others have shown that similar reactions within oil droplets can help them do more than just move. They can travel along chemical gradients, a trick called chemotaxis which many bacteria use to find food and avoid threats. By doing so, one oil droplet has even managed to "solve" a complex maze (New Scientist, 23 January 2010, p 8).
Hanczyc's recent studies show that in addition to moving, his droplets "can sense and respond to the local environment", he says. When two droplets approach one another they change course to avoid colliding, or they circle each other like partners in a Viennese waltz.
More impressively still, it seems they even have a form of memory. Hanczyc videoed droplets stopping and starting, and measured the times between successive halts. He found that the decision to stop or go did not fit a random distribution. Instead, the droplets' behaviour at any one point was affected by the behaviour they had displayed previously. Like maze-solving, such crude memories have been observed in primitive life - amoebas, for example, are more likely to turn left if their previous turn was to the right.
Magic gunk
But it is Hanczyc's latest experiments that have attracted most interest from early-life researchers. He has ditched the oleic anhydride and is now injecting his droplets with the tar from a Miller-Urey-style experiment. The gunk has much the same effect on the droplets as the oleic anhydride does. Fuelled by the tar, the droplets still move through solutions and can still sense and respond to one another. Hanczyc plans to begin testing their "memories" soon, too.
The droplets are still enclosed in a thin layer of oleic acid to lower surface tension, but some of the tar reacts directly with the water outside the droplet to create an acidic product. This skims to the opposite side of the droplet and establishes a pH gradient. Just like what happens in the oleic acid experiments, the tar triggers internal convection currents, and the droplet is driven forward (see diagram).
If the oil droplets exhibit so many lifelike properties, and can be fuelled by the tarry residues of the kind thought to exist on the primordial Earth, could Hanczyc have arrived at something akin to an origin-of-life scenario? Last week he presented his work at the Royal Society's Chemical Origins of Life and its Early Evolution conference in London, providing an opportunity to test reactions among other early-life researchers.
It's a "lovely piece of work", says John Sutherland of the Medical Research Council's Laboratory of Molecular Biology in Cambridge, UK. Does that mean we are all descended from primordial oil droplets? Biologists remain to be convinced. To be candidates for the origin of life, such droplets must have been able to form and flourish on the primitive Earth, and although the droplets consume Miller-Urey tar, the nitrobenzene that forms their "bodies" probably did not exist back then. "Perhaps with tinkering they can be made more plausible," says Jason Dworkin of NASA's Goddard Space Flight Center in Greenbelt, Maryland.
Hanczyc concedes the point, and has begun repeating the experiments using mineral oil, which is more likely to have existed. "The movement is slower but it is there," he says.
Another issue for the droplets is that they have no genes. That's a serious problem, says Jeffrey Bada of the University of California, San Diego, who did his PhD under Stanley Miller. "The working definition of life is a self-reproducing system that makes imperfect copies of itself," he says. "If it doesn't evolve, then it isn't relevant." Hanczyc is working on making the droplets divide but that won't, of course, give them genes.
Sutherland retains a more open mind. Hanczyc's droplets are a useful proof of principle, he says, because they have not one but several properties of life. He thinks that origin-of-life research is overly concerned with creating individual components of life, like self-replication or metabolism. Because these elements depend on each other, the approach runs up against endless chicken-and-egg paradoxes. "We all look at little bits of the problem."
Instead, he reckons there is a "sweet spot": a chemical set-up that gives rise to a suite of lifelike properties all at once. Although the exact conditions will likely be complicated, Sutherland says they could rapidly give rise to something with many of the elements of life.
And that is precisely what Hanczyc has done. Even if his oil droplets don't represent the first flowering of life on Earth, they hint that if you get the starting conditions right, basic life may spring forth almost fully formed.
Links, diagrams and film here:
http://www.newscientist.com/article/mg20928023.900-primordial-pacman-oil-droplet-hints-at-lifes-origin.html?full=true
If you ignore the inappropriate metaphors, and the rather odd use of "memory", this looks promising.
Primordial Pac-Man: Oil droplet hints at life's origin
02 March 2011 by Michael Marshall
Simple oil drops show that if you get the conditions right, basic life may emerge almost fully formed
WHEN Stanley Miller and Harold Urey created amino acids by shooting sparks through a "primordial atmosphere" of methane, ammonia, hydrogen and water, biologists thought a full understanding of the origins of life was within reach. Almost 60 years on from the most famous origin-of-life experiment of them all, we're still waiting.
Could that be because biologists have been looking at the wrong part of the experiment? A fresh look at the tarry residue left behind in a Miller-Urey-style experiment has revealed something remarkable: when injected into a simple oil droplet, the gunk endows it with spookily lifelike behaviour - although crucially it cannot yet reproduce. Like Pac-Man, an oil droplet doped with tarry junk can sense and respond to its neighbours and move towards "food" sources.
Although the Miller-Urey set-up is best known for producing amino acids, its primary product is a complex hydrogen cyanide polymer that looks like black tar and has mostly been ignored. "For the most part, people filtered it off and threw it down the drain," says Bob Minard of Pennsylvania State University in University Park.
Martin Hanczyc at the University of Southern Denmark in Odense and his colleagues are being less dismissive. They previously showed that oil droplets doped with oleic anhydride have attributes generally associated with life, and now say that the overlooked gunk can imbue oil with the same properties.
Hanczyc spent four years experimenting with simple oil droplets. His earliest studies involved lacing drops of oily nitrobenzene with oleic anhydride before floating them in an alkaline aqueous solution. Immediately, the droplets began to jerk about, and moments later they shot off in straight lines.
Each droplet is powered by a simple chemical process. Oleic anhydride at the surface reacts with the surrounding water to create oleic acid, a surfactant that lowers the droplet's surface tension. By chance, the reaction is fastest at one point on the droplet's surface. As a result, this reactive hotspot draws oleic anhydride from within the droplet, setting up internal convection currents.
Meanwhile, the oleic acid skims across the droplet's surface to gather on the opposite side, setting up a pH gradient. This, along with the internal convection currents, is enough to force the droplet forwards through the aqueous solution (Journal of the American Chemical Society, vol 129, p 9386). Hanczyc compares the reactions happening in the hotspot to a metabolism, where fuel is broken down to produce the energy that drives the droplet forward.
Others have shown that similar reactions within oil droplets can help them do more than just move. They can travel along chemical gradients, a trick called chemotaxis which many bacteria use to find food and avoid threats. By doing so, one oil droplet has even managed to "solve" a complex maze (New Scientist, 23 January 2010, p 8).
Hanczyc's recent studies show that in addition to moving, his droplets "can sense and respond to the local environment", he says. When two droplets approach one another they change course to avoid colliding, or they circle each other like partners in a Viennese waltz.
More impressively still, it seems they even have a form of memory. Hanczyc videoed droplets stopping and starting, and measured the times between successive halts. He found that the decision to stop or go did not fit a random distribution. Instead, the droplets' behaviour at any one point was affected by the behaviour they had displayed previously. Like maze-solving, such crude memories have been observed in primitive life - amoebas, for example, are more likely to turn left if their previous turn was to the right.
Magic gunk
But it is Hanczyc's latest experiments that have attracted most interest from early-life researchers. He has ditched the oleic anhydride and is now injecting his droplets with the tar from a Miller-Urey-style experiment. The gunk has much the same effect on the droplets as the oleic anhydride does. Fuelled by the tar, the droplets still move through solutions and can still sense and respond to one another. Hanczyc plans to begin testing their "memories" soon, too.
The droplets are still enclosed in a thin layer of oleic acid to lower surface tension, but some of the tar reacts directly with the water outside the droplet to create an acidic product. This skims to the opposite side of the droplet and establishes a pH gradient. Just like what happens in the oleic acid experiments, the tar triggers internal convection currents, and the droplet is driven forward (see diagram).
If the oil droplets exhibit so many lifelike properties, and can be fuelled by the tarry residues of the kind thought to exist on the primordial Earth, could Hanczyc have arrived at something akin to an origin-of-life scenario? Last week he presented his work at the Royal Society's Chemical Origins of Life and its Early Evolution conference in London, providing an opportunity to test reactions among other early-life researchers.
It's a "lovely piece of work", says John Sutherland of the Medical Research Council's Laboratory of Molecular Biology in Cambridge, UK. Does that mean we are all descended from primordial oil droplets? Biologists remain to be convinced. To be candidates for the origin of life, such droplets must have been able to form and flourish on the primitive Earth, and although the droplets consume Miller-Urey tar, the nitrobenzene that forms their "bodies" probably did not exist back then. "Perhaps with tinkering they can be made more plausible," says Jason Dworkin of NASA's Goddard Space Flight Center in Greenbelt, Maryland.
Hanczyc concedes the point, and has begun repeating the experiments using mineral oil, which is more likely to have existed. "The movement is slower but it is there," he says.
Another issue for the droplets is that they have no genes. That's a serious problem, says Jeffrey Bada of the University of California, San Diego, who did his PhD under Stanley Miller. "The working definition of life is a self-reproducing system that makes imperfect copies of itself," he says. "If it doesn't evolve, then it isn't relevant." Hanczyc is working on making the droplets divide but that won't, of course, give them genes.
Sutherland retains a more open mind. Hanczyc's droplets are a useful proof of principle, he says, because they have not one but several properties of life. He thinks that origin-of-life research is overly concerned with creating individual components of life, like self-replication or metabolism. Because these elements depend on each other, the approach runs up against endless chicken-and-egg paradoxes. "We all look at little bits of the problem."
Instead, he reckons there is a "sweet spot": a chemical set-up that gives rise to a suite of lifelike properties all at once. Although the exact conditions will likely be complicated, Sutherland says they could rapidly give rise to something with many of the elements of life.
And that is precisely what Hanczyc has done. Even if his oil droplets don't represent the first flowering of life on Earth, they hint that if you get the starting conditions right, basic life may spring forth almost fully formed.
Links, diagrams and film here:
http://www.newscientist.com/article/mg20928023.900-primordial-pacman-oil-droplet-hints-at-lifes-origin.html?full=true
If you ignore the inappropriate metaphors, and the rather odd use of "memory", this looks promising.