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Triple Helix — Designing a New Molecule of Life
Anti-Globalism sends in this quote from Scientific American about attempts to synthesize molecules that function as well or better than the natural building blocks of life:
"A molecule that some researchers study in pursuit of this vision is peptide nucleic acid (PNA), which mimics the information-storing features of DNA and RNA but is built on a proteinlike backbone that is simpler and sturdier than their sugar-phosphate backbones. ... Many studies have demonstrated PNA's suitability for modifying gene expression, mostly in molecular test-tube experiments and in cell cultures. Studies in animals have begun, as has research on ways to transform PNA into drugs that can readily enter a person's cells from the bloodstream. ... Some scientists have suggested that PNAs or a very similar molecule may have formed the basis of an early kind of life at a time before proteins, DNA and RNA had evolved. Perhaps rather than creating novel life, artificial-life researchers will be re-creating our earliest ancestors."
Soon we will have the "quatro helix DNA" and then 5 helixes and so on.
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Don't make the mistake of anthropomorphizing evolution. There is no committee that considers all possible solutions and states "This is the best one". Evolution is a case of what happens happens and what doesn't die out is what's left and so considered successful.
It is entirely possible that there are much more efficient ways for life to exist or function, but are different than the way life happened to happen here on earth. Or it could be that life DID happen that way but the methodology was not optimal for the environment at the time so the DNA/RNA based forms outlived them.
Ice Cream has no bones.
Several years ago, I worked as a chemist for a small biochemical company in the UK, making modified olignucleotides and PNA.
IIRC, PNA had one outstanding feature: It binds to a complementary DNA strand much stronger than DNA itself (due in part to the lack of repulsion in the protein backbone. DNA's phosphate backbone is negatively charged).
Sadly, this means that two stands of PNA will bind extremely strongly to each other, and the forces required to unpair (part of the replication process) them would require different, "stronger" enzymes - so no chance of cell division, and no chance of life. (Still sounds cool though!)
Perhaps PNA is too stable, so that life forms based on it couldn't evolve through mutations quickly enough to adapt to changes.
Possibly because evolution requires a molecule that is not too stable.
I'm just speculating here... the basis of evolution is random changes in DNA which result in a phenotype which may confer an advantage to one individual over another. If you have an absolutely error-proof system of DNA replication, you effectively limit evolution. But you don't want too many changes at one time, which would actually be detrimental. The ideal balance is somewhere in between... and it may be that a DNA double-helix with a sugar backbone is the ideal molecule for allowing just the right frequency of random changes for evolution to progress.
That said, I agree that it seems unlikely that such a fundamental shift as switching from PNA to DNA/RNA seems unlikely to have fluked itself into existence unless there's some tradeoff in, eg, efficiency of producing the molecules, or the difference is really pretty minor after all.
How is "evolutionary progress" not "progress"? This is the only measuring stick I've used. If PNA had indeed existed before DNA or RNA (as the article seems to suggest), and was snuffed out, then clearly it didn't function better than RNA/DNA when it came to surviving in a particular environment, or evolving. What is the "functionality" of an organism if not survival and procreation?
in a particular environment, or evolving
This is the exact point i'm trying to make that you seem to be missing. Survival in a particular environment does not mean a life form is best at surviving in any environment. If there was a long enough period where the stimuli and environmental pressures involved made RNA/DNA based life the most efficient, then there would be none of the alternative life forms remaining when the pressures change.
Just because a species goes extinct does not mean that that species was not "fit for survival" at all. It simply means that the species was not fit for survival given the pressures and stimuli of the time they went extinct.
The only measuring stick that matters to evolution is procreation, you're right about that. The part people forget is everything else that happens is just rolls of the dice with no specific desired outcome. If it helps the species survive the current pressures, the trait remains. If not, it either dies out or falls recessive within the species gene pool.
Ice Cream has no bones.
Where did I assume that? What i'm saying is there IS no way to define a peak, since its variable dependant on the time frame and environmental pressures as to what is considered "optimal".
Ice Cream has no bones.
Yeah sugar-phosphate is just too scary. Lets create life based on stuff we aren't made of like lead and mercury.
I can conceive of a situation where such a molecule might actually be selected against. If the molecule were "too" stable and inhibited molecular evolution, it's quite possible that early life with essentially a "broken" system like RNA, which made events like transcription errors and insertions more likely, then it's quite possible that RNA could have won out over the technically "better" molecule simply out-evolving it.
The world's burning. Moped Jesus spotted on I50. Details at 11.
They want to make a redheaded punk-haired girl, so it's a noble cause. ;)
You can hold down the "B" button for continuous firing.
PNA might function better than DNA/RNA, but its cost (resources, time to create) is higher and couldn't be afforded by the first organisms.
By your logic humans who wouldn't survive a nuclear war are less efficient than roaches that would survive it.
Just, roaches will never start a nuclear war in the first place.
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"A synthetic molecule called peptide nucleic acid (PNA) combines the information-storage properties of DNA with the chemical stability of a proteinlike backbone."
I see two possible reasons PNA was not selected.
First, as others have said, it's stable. Evolution requires a bit of mutation to move forward. Out of a billion mistakes, maybe 1(or less) will cause an organism to be more 'fit.' So, you have a balancing act between errors and fitness, where too many errors reduce an organisms fitness and two few reduce it's adaptability.
Second, the protien backbone is possibly biologically expensive. There are many who believe advances in human intellegence is linked very closely with the availability of massive amounts of protein provided by cooking our food. So, the availability and neccesity of protein could be limiting factors in evolution. So any process which provides the same function with significantly less biological cost, even if slightly inferior in other ways, may be selected.
If it helps the species survive the current pressures, the trait remains.
Oops! You mean, "If it doesn't hurt the species' survival under the current pressures, the trait remains."