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lpetrich
2003-Jan-25, 07:51 AM
According to this Astrobiology Magazine article (http://www.astrobio.net/news/print.php?sid=357), yes.

According to William Martin of Heinrich-Heine University in Duesseldorf, Germany, and Michael Russell of the Scottish Environmental Research Centre in Glasgow, hydrothermal vents represent a good possible site for the origin of life for a very interesting reason. Hydrothermal vents produce deposits of iron sulfide that have a honeycomb-like microstructure with "cells" having sizes of a few microns. And Martin and Russell suggest that these "cells" could have allowed the earliest life to have a cellular structure before those organisms worked out how to produce cell membranes.

The catalytic properties of the deposits' surface would have induced numerous chemical reactions in the flowing-by hydrothermal-vent fluids, some of which could well have led to the origin of life. A scenario first proposed by Gunter Wachtershauser some years back; he proposed that life originated from iron-sulfur chemistry on pyrite (iron sulfide) rocks.

But can this happen in the laboratory? George Cody and his colleagues at the Carnegie Institution of Washington succeeded in producing pyruvic acid, a common metabolic intermediate, with the help of iron sulfide, formic acid, and alkyl thiol that were heated and pressurized together.

This conclusion agrees with the results of some attempts to work backwards from present-day organisms. One enzyme important in biosynthesis, ferredoxin, has an iron-sulfur core -- and according to one reconstruction, its ancestral form had a negatively-charged tail, making it adapted to sticking to mineral surfaces with their positively-charged ions.

Also, this ancestral form was made out of relatively simple amino acids, those relatively easy to produce by prebiotic chemistry. By comparison, proteins associated with cell membranes tended to have more difficult-to-produce amino acids that would have been later acquisitions or inventions.

At least according to this paper:

Davis BK.
Molecular evolution before the origin of species.
Prog Biophys Mol Biol 2002 May-Jul;79(1-3):77-133
At this PubMed entry (http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12225777&dopt=Abstract).

I'm mentioning this here because it suggests that the origin of Earth life was a result of processes that can easily happen on planets with similar overall properties; nice to see origin-of-life research getting somewhere.

cable
2003-Jan-25, 10:44 AM
the big problem is the cellular membrane.
had they succeeded to create that membrane in lab ??

I've read that if we take DNA from a cell, it still remains in life for a while, until it's impossible to produce some essential stuff ...

seems like life started with that membrane, then DNA was lately incorporated.

lpetrich
2003-Jan-25, 04:56 PM
According to this hypothesis, the original living things had been bounded by the mineral deposits that they had inhabited. With cell membranes being a later invention.

And after cell membranes and cell division were invented, DNA was invented as a modification of RNA -- the first organisms apparently had RNA genomes.

cable
2003-Jan-25, 06:43 PM
On 2003-01-25 11:56, lpetrich wrote:
According to this hypothesis, the original living things had been bounded by the mineral deposits that they had inhabited. With cell membranes being a later invention.

And after cell membranes and cell division were invented, DNA was invented as a modification of RNA -- the first organisms apparently had RNA genomes.

membrane is not a simple "packaging".
according to a theory called "irreducible complexity", this complex structure must have been enginered to fulfill its duty from the start, not by stepping evolution ...

the question is who invented that membrane ??
- by chance ? ... hummm !!
- evolved by integrating environmental data. yet membrane has not yet DNA to memorize these data.
- from an ET planet ? that doesn't solve the problem.

more on membrane:
http://cellbio.utmb.edu/cellbio/membrane.htm
http://cellbio.utmb.edu/cellbio/membrane_intro.htm#Architecture

lpetrich
2003-Jan-25, 07:27 PM
What makes a cell membrane "irreducibly complex"?

A cell membrane is a simple structure: a lipid bilayer, much like a soap bubble. And what is "irreducibly complex" about soap bubbles?

Furthermore, evolution can produce irreducibly complex structures. Consider the societies of honeybees. Their queens have no way of surviving without their workers, so how could one get from a solitary bee that does everything to a queen that only lays eggs? But most species of social bees, like bumblebees, have queens that can live on their own when necessary; this provides a pathway to honeybee always-dependent queens.

lpetrich
2003-Jan-25, 08:15 PM
But back to the main point. If Earth life had originated from hydrothermal vents, then we may ask where else in the Universe that hydrothermal vents can form.

Hydrothermal vents are produced by water flowing through heated rocks and escaping to the surface. This means that they can only form on terrestrial planets with liquid water, like the Earth.

Where else in the Solar System might hydrothermal vents form or have formed?

Mars and Europa are two likely candidates.

However, Mars is too cold for liquid water at the present time, suggesting that it had always been too cold for liquid water, barring a super-greenhouse-effect atmosphere early in its history. And its numerous riverbeds are most likely not evidence of continuously-present liquid water, but instead evidence of giant floods of something, floods much like the Missoula and Altai giant floods of the Earth's Pleistocene.

Europa has enough internal heat to cause its surface to become reformed relatively recently; this heat comes from its orbit resonances with the other Galilieans, resonances which induce a forced orbit eccentricity, which in turn induces variations in Jupiter-caused tides. This mechanism is much stronger in Io, where it produces the only known active extraterrestrial volcanoes.

So there could be hydrothermal vents underneath Europa's deep ocean.

cable
2003-Jan-25, 08:31 PM
On 2003-01-25 14:27, lpetrich wrote:
What makes a cell membrane "irreducibly complex"?
A cell membrane is a simple structure: a lipid bilayer, much like a soap bubble. And what is "irreducibly complex" about soap bubbles?

did man already synthesized this "simple" structure ??


Furthermore, evolution can produce irreducibly complex structures. Consider the societies of honeybees. Their queens have no way of surviving without their workers, so how could one get from a solitary bee that does everything to a queen that only lays eggs? But most species of social bees, like bumblebees, have queens that can live on their own when necessary; this provides a pathway to honeybee always-dependent queens.


u r applying IC to the whole bee society. I dunno.
as for mrmbrane, IC means membrane could not have been much simpler structure, that evolution brought it to current level.
ie. it's current structure or it won't work.

likewise, the mousetrap. all components are needed. it u take one of them , system won't work. so mousetrap came as a whole thing at one time.

cable
2003-Jan-25, 08:50 PM
Hydrothermal vents are produced by water flowing through heated rocks and escaping to the surface. This means that they can only form on terrestrial planets with liquid water, like the Earth.

Where else in the Solar System might hydrothermal vents form or have formed?

why should life at another planet mimic life on earth ??
life at other planet could be based on replicating stuff which has nothing to do with our DNA, even if that planet has same physical conditions as earth ....
and there's nothing yet to prove the universality of DNA .

VanBurenVandal
2003-Jan-25, 09:41 PM
Even if DNA exists on other planets, it still may not be universal. Here on good ol’ Terra DNA is right-handed (the direction the helix “spins”). What’s to say other civilizations won’t be based off of left-handed DNA? Then, no matter how similar the two biospheres are, they would forever be fundamentally different. Just one of those potential oddities of life…

lpetrich
2003-Jan-25, 10:19 PM
Here is how honeybee societies are irreducibly complex: queens depend on workers for food, shelter, protection, etc., while workers depend on queens to replenish their numbers.

Thus, honeybees found new hives by swarming; a queen takes a swarm of workers with her in search of a new hive location. However, she stays buried in the swarm as workers leave it to look for good hive locations.

However, bumblebee societies are not IC, because bumblebee queens do all the necessary tasks when they found a new hive, collecting nectar and pollen and feeding it to her grubs.

And cell membranes are not irreducibly complex either; their primary function, separating cell interior from exterior, does not require any of the various structures that are embedded in them. These structures are later elaborations, made possible by an already-existing membrane.

lpetrich
2003-Jan-25, 10:21 PM
I agree that extraterrestrial life need not use DNA as its heredity molecule.

And even if it does use DNA, it may have a version with different asymmetries.

But such possibilities do not cause any difficulty for the hydrothermal-vent-origin scenario.

zwi
2003-Jan-26, 03:47 AM
Even if DNA exists on other planets, it still may not be universal. Here on good ol’ Terra DNA is right-handed (the direction the helix “spins”). What’s to say other civilizations won’t be based off of left-handed DNA? Then, no matter how similar the two biospheres are, they would forever be fundamentally different. Just one of those potential oddities of life…


I am no expert on this but I strongly suspect that a left handed DNA will not work
Its a matter of the shape of the possible molecules and shapes of the proteins involved

Zwi

<font size=-1>[ This Message was edited by: zwi on 2003-01-25 22:49 ]</font>

lpetrich
2003-Jan-26, 07:44 AM
Zwi:

I am no expert on this but I strongly suspect that a left handed DNA will not work
Its a matter of the shape of the possible molecules and shapes of the proteins involved.

That's only a difficulty if only the DNA gets reflected; if one reflects all of the molecules, then the result will have the same functionality as before, because of the four fundamental forces, only the weak interaction is reflection-sensitive. And that is VERY weak at atomic scales.

cable
2003-Jan-26, 10:53 AM
But such possibilities do not cause any difficulty for the hydrothermal-vent-origin scenario.

suppose we find exactly same hydrothermal-vent at a remote planet.
should we say, because this vent produced life on earth, then it must do the same on that planet ??
is this "vent-life" we have on earth, the only and unique life possibility ??

we dont have definitive answer.

we are at molecular level. there where QM is doing strange things.
think about chance, uncertainty, decoherence ...

DStahl
2003-Jan-27, 01:30 AM
Cable: "...according to a theory called 'irreducible complexity', this complex structure [cell membrane] must have been enginered to fulfill its duty from the start, not by stepping evolution."

Ieptrich addressed this nicely, but here's a bit more. Researchers have made various structures that could be prototypes of simple cell membranes:

"Harold Morowitz has proposed that the formation of closed, membrane vesicles was an early event in cellular evolution. Lipid molecules spontaneously form membrane vesicles or liposomes. (Beginnings of Cellular Life, 1992, Yale University Press). Consider the following properties of membrane vesicles, which are also the properties of cells."

"1) They maintain separate stable phases in an aqueous environment."

"2) They maintain different chemical compositions between intra- and extra-cellular compartments."

"3) They maintain substantial transbilayer electrical voltages, pH differences, and oxidation potentials (necessary for chemiosmotic processes)."

"4) They form spontaneously from abiotically formed amphipathic lipid molecules."

"'What is impressive in simply listing the properties of vesicles is how many cellular features are already present in these simple systems. Strong reasons for assuming the importance of vesicles in biogenesis are their spontaneous formation and the continuity they make with contemporary cells in so many ways'". Reference (http://www.utdallas.edu/~cirillo/nats/day18.htm)

I think that cell membranes are not so much a case of irreducible complexity as one of an overwhelmingly successful development. If self-replicating structures first appeared in a specific microenvironment in pores in rock, or between layers of clay, then until they could contain and carry their own microenvironment along inside a coating of some sort they couldn't spread into the larger environment. Because the "invention" was so successful virtually all life today has some kind of cell membrane (what about viruses?). At least that's my guess.

cable
2003-Jan-27, 11:42 AM
DStahl,


Researchers have made various structures that could be prototypes of simple cell membranes:

let's take one of them, ad fill it with the stuff we have in a living cell. will it work ??
was it just a good chance, that curent membrane is the right one, or did life tried other membranes and found them inadecate ??

ther's IC, kuz no simpler structure will work with CURRENT cell machinery, tissue, immunological system that took place on membrane surface ....
ie. those structure u talking about, could form perhaps another biology.
that's my opinion.


Because the "invention" was so successful virtually all life today has some kind of cell membrane (what about viruses?). At least that's my guess.


I wonder if that successful "invention" emerged just by chance ??

as for viruses, some consider them as living entitities. some not, kuz they cannot replicate by themselves. in fact they divert cell machinery to do the job.
so one can say: no membrane , no life.

Mainframes
2003-Jan-27, 01:49 PM
On 2003-01-27 06:42, cable wrote:
DStahl,


Researchers have made various structures that could be prototypes of simple cell membranes:

let's take one of them, ad fill it with the stuff we have in a living cell. will it work ??
was it just a good chance, that curent membrane is the right one, or did life tried other membranes and found them inadecate ??

ther's IC, kuz no simpler structure will work with CURRENT cell machinery, tissue, immunological system that took place on membrane surface ....
ie. those structure u talking about, could form perhaps another biology.
that's my opinion.


Because the "invention" was so successful virtually all life today has some kind of cell membrane (what about viruses?). At least that's my guess.


I wonder if that successful "invention" emerged just by chance ??

as for viruses, some consider them as living entitities. some not, kuz they cannot replicate by themselves. in fact they divert cell machinery to do the job.
so one can say: no membrane , no life.




I imagine that a few different membranes were 'tried' out but as they failed life didn't emerge using them. Once a successful design was found, life couldn't help but explode and take over...

lpetrich
2003-Jan-27, 06:56 PM
Cable, the ancestral cell membrane would not have been as fancy as present-day cell membranes; it would have been a simple lipid bilayer and nothing more. All the other stuff that you are so worried about would be later inventions.

And how would one get from mineral "cells" to membrane-bounded cells? By the membrane originally blocking pores in the mineral deposits. Once it is present, however, proteins could stick to that membrane, and become adapted for residence there.

Membrane proteins need no fancy way of getting into membranes; they have hydrophobic (water-repellent) domains that give them an affinity for membrane interiors in "like dissolves like" fashion.

cable
2003-Jan-27, 09:32 PM
I imagine that a few different membranes were 'tried' out but as they failed life didn't emerge using them. Once a successful design was found, life couldn't help but explode and take over...

could be.
in this case, I see this earlier membrane has not been improved in many evolutionary steps til nowadays membrane.
likewisely, we threw away our solar clock, and start a new concept: the mechanical clock. no evolution between the 2 models, just a "quantum leap".

tracer
2003-Jan-27, 11:36 PM
Everone knows that life arose on the Earth in the form of bions (http://www.netcom.com/~rogermw/Reich/bions.html). /phpBB/images/smiles/icon_wink.gif

DStahl
2003-Jan-28, 09:21 AM
Cable: "...as for viruses, some consider them as living entitities. some not, kuz they cannot replicate by themselves. in fact they divert cell machinery to do the job.
so one can say: no membrane , no life."

On the other hand, if one considers an organic system that reproduces itself life, then viruses are alive. If viruses are alive, then existing species show that life can and does exist without cell membranes.

More importantly, when you say "no membrane, no life" you address only the Earth as we see it now. It seems to me quite possible that early replicating systems got their start in unique micro-environments and then, when a structure like Fox's lipid vesicles or like Oparin's coacervates was available, natural selection guarranteed that any self-replicating system that happened to be able to take advantage of these vesicles or coacervates would spread into the environment at large.

The meta-concept is that evolution over long timespans exerts an immensely leveraged influence on replicating systems. No, scientists cannot build perfect cell membranes from scratch. Neither can they build an organic eyeball--but existing creatures show us light-sensitive organs spanning the continuum of complexity: intracellular rhodopsin allows single-celled euglena to detect light; planaria have flat eyespots without lenses; snails have photo-sensitive tissue in a globe shape with a pinhole aperture but no lens; and of course squids and men have semi-spherical eyeballs with a lens. All these variations on light-detecting organs help these various creatures live in the world.

Of course, if you require that all evolution be reproducible on lab tables then I suppose there is no reason for you to believe that dogs are descended from wolves--scientists cannot make a dog in a lab, you see.

Karl
2003-Jan-28, 04:56 PM
On 2003-01-27 16:32, cable wrote:
likewisely, we threw away our solar clock, and start a new concept: the mechanical clock. no evolution between the 2 models, just a "quantum leap".


Wouldn't you consider a water clock to be an intermediate form? /phpBB/images/smiles/icon_smile.gif

tracer
2003-Jan-28, 07:33 PM
On 2003-01-28 04:21, DStahl wrote:
It seems to me quite possible that early replicating systems got their start in unique micro-environments and then, when a structure like Fox's lipid vesicles or like Oparin's coacervates was available,


Fox's vesicles weren't lipids, they were proteinoid microspheres (http://www.siu.edu/~protocell/). Lipospheres were discovered later, by someone else.