https://www.nasa.gov/topics/solarsystem/features/dna-meteorites.html
But DNA created in space ? What does that mean , really ?
But DNA created in space ? What does that mean , really ?
The Origin of DNA ? NASA SAYS SPACE .
- Thread starter river
- Start date
So your saying that in space , what builds DNA , the building blocks of DNA , are separate ?
DaveC426913
Valued Senior Member
Yes. Nucleotides are the "bricks" of DNA. Essentially, they are the foundation for the base pairs
that, in bulk, encode the genetics in DNA.
The nucleotides may have formed in space - that does not suggest that DNA itself formed in space.
that, in bulk, encode the genetics in DNA.
The nucleotides may have formed in space - that does not suggest that DNA itself formed in space.
Yet so far as I have found , none are found in Nature in free form , meaning not by themselves . The bricks , as you call them , Dave , a foundation of DNA , are not found independent of the other base pairs .
exchemist
Valued Senior Member
The link provided in the OP explains what kind of building block has been found. These are, apparently molecules such as adenine, guanine etc.
These are not nucleotides, or even nucleosides, but some of the components of these - the naked forms of the individual "bases" found in the DNA structure.
DNA, being such a highly complex structure, can be seen as made up, like a car, of various sub-assemblies (nucleotides), each of which involves further sub-assemblies (nucleosides, phosphate groups) and each of these is itself made up of many components, one of which is a "base", itself a fairly complex polyatomic molecule - by the standards of interstellar space at least.
By way of example, more on adenine here: https://en.wikipedia.org/wiki/Adenine This refers to the Nasa finding, which dates from 2011 apparently. I find it interesting that they say it has complex photochemistry that helps explain its survival under UV light exposure. (I'd like to know more about that - though obviously as it is a 2-ring heterocyclic aromatic compound, it would be expected to have a number of interesting options in its excited states.)
These are not nucleotides, or even nucleosides, but some of the components of these - the naked forms of the individual "bases" found in the DNA structure.
DNA, being such a highly complex structure, can be seen as made up, like a car, of various sub-assemblies (nucleotides), each of which involves further sub-assemblies (nucleosides, phosphate groups) and each of these is itself made up of many components, one of which is a "base", itself a fairly complex polyatomic molecule - by the standards of interstellar space at least.
By way of example, more on adenine here: https://en.wikipedia.org/wiki/Adenine This refers to the Nasa finding, which dates from 2011 apparently. I find it interesting that they say it has complex photochemistry that helps explain its survival under UV light exposure. (I'd like to know more about that - though obviously as it is a 2-ring heterocyclic aromatic compound, it would be expected to have a number of interesting options in its excited states.)
I'd like to know more about that - though obviously as it is a 2-ring heterocyclic aromatic compound, it would be expected to have a number of interesting options in its excited states.
Why , what is it about being a , 2-ring heterocyclic aromatic compound , that stirs your curiosity , enough to know more about this , compound ?
I would like to know .
river
DaveC426913
Valued Senior Member
On Earth. A warm and chemically very active cauldron. It would be pretty much impossible for a given nuceolotide not to be incorporated into some passing form of life.
That says nothing about the vacuum of space (such as in an asteroid) - where active molecules are few and far between, and temps are far, far below any activation temperature. They can't build up into proteins.
i.e. nucleotides and DNA are pretty much found (and not found) exactly where you'd expect them to be found (and not found).
exchemist
Valued Senior Member
I have not found more on adenine but I did find this interesting paper suggesting that the base pair guanine-cytosine as arranged in DNA has a much broader UV absorption band than other possible arrangements: http://www.pnas.org/content/pnas/102/1/20.full.pdf
This suggests that the lifetime of the excited state formed by UV absorption is far shorter for this arrangement than for others, due to internal conversion, that is, non-radiative ways of redistributing the energy and returning the molecule to the ground state. (Due to the Uncertainty Principle, a short lifetime implies an uncertainty in energy, hence a broadening of the absorption band.)
The authors suggest that this would make the base pair in its DNA arrangement more resistant to degradation by UV than expected, enabling it to hang around longer for other reactions to occur. Cool stuff.
perhaps chemistry at it's most basic level is primed for life in space, like the lengthening telomeres on chromosomes of astronauts in orbit. (see "primed for life" topic, Exobiology)
Gawdzilla Sama
Valued Senior Member
The Daily Mail will be talking about "Alien DNA found on Earth!"
exchemist
Valued Senior Member
I'm not sure that means anything. Chemistry is a consequence of physics: it is what it is.
I think it is probably more useful to say that the chemistry of life may have arisen the way it has due to the ability of certain strcutures to withstand the early environment - a form of pre-biological natural selection, if you like.
Disagree
Chemistry is about reactions of physical things to physical things . Physics is the consequence of these reactions .
DaveC426913
Valued Senior Member
No. There are no reactions of things to other things without physics.
Physics occurs whether or not chemistry occurs.
Chemistry does not occur without physics there to make it occur.
Chemistry is an emergent property of physics.
Nope. Physics underlies chemistry, not the other way around.
Yazata
Valued Senior Member
The astrobiologists at NASA-Ames (a very interesting bunch) have recently discovered that deoxyribose, the sugar that forms the backbone of DNA (its 'D') forms in laboratory conditions that mimic outer space as well.
https://www.nature.com/articles/s41467-018-07693-x
This still isn't convincing evidence that DNA originated in space, but more and more of its "parts" may have.
I'd like to see some evidence that deoxyribose and the nucleobases that form out there can polymerize in space conditions to form something like DNA chains. That would be a epochal discovery.
If chemical replicators originally appeared out in space, I can imagine their 'delight' when they rain down on a rich environment like a planet where their chemistry can really take off, elaborating through natural selection into cells and full-blown metabolism.
Unfortunately, DNA replication on earth requires protein enzymes, which require DNA (and a whole molecular biological apparatus) for their synthesis. That creates a bit of a chicken and egg problem. (Which came first, proteins or DNA? Each seem to be dependent on each other.)
Which is why many biologists prefer the 'RNA world' theory of the origin of life, since RNA can serve as both a catalyst (eliminating the initial need for the proteins) and an information storage mechanism.
So... if DNA can somehow form in space without the need for the protein catalysts, that would be huge, overturning the 'RNA world' hypothesis.
Of course right now we are a long way away from that.
https://www.nature.com/articles/s41467-018-07693-x
This still isn't convincing evidence that DNA originated in space, but more and more of its "parts" may have.
I'd like to see some evidence that deoxyribose and the nucleobases that form out there can polymerize in space conditions to form something like DNA chains. That would be a epochal discovery.
If chemical replicators originally appeared out in space, I can imagine their 'delight' when they rain down on a rich environment like a planet where their chemistry can really take off, elaborating through natural selection into cells and full-blown metabolism.
Unfortunately, DNA replication on earth requires protein enzymes, which require DNA (and a whole molecular biological apparatus) for their synthesis. That creates a bit of a chicken and egg problem. (Which came first, proteins or DNA? Each seem to be dependent on each other.)
Which is why many biologists prefer the 'RNA world' theory of the origin of life, since RNA can serve as both a catalyst (eliminating the initial need for the proteins) and an information storage mechanism.
So... if DNA can somehow form in space without the need for the protein catalysts, that would be huge, overturning the 'RNA world' hypothesis.
Of course right now we are a long way away from that.
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