In a galaxy far, far away, aliens may have eight-letter DNA – like the kind NASA-backed boffins just crafted Scientists say they have crafted a semi-synthetic DNA and RNA molecular system that is able to usefully store genetic information. It's hoped that alien lifeforms exist out there with similar exotic biological structures. In other words, life beyond our planet could be using something like these engineered DNA molecules, and …
I wonder if using all 8 would be too inefficient for life.
A 4-base system means that a single base-pair can encode 2 bits of information. Doubling to 8 bases means having to evolve, code for and run twice as many base synthesis pathways in return for making a base-pair encode 3 bits. It would mean a 2 base-pairs would be adequate as a codon, shortening the number of base pairs needed in a genome by a third. However the amount of non-coding DNA found in chromosomes suggests that number of base pairs isn't necessarily an issue. What's more the 3 base-pair codon has an element of redundancy arranged so as to minimise the damage mutations cause. A 2 base-pair codon would have the same amount of redundancy (assuming the same number of amino acids to be represented) but I'm not sure it would provide the same degree of damage limitation.
It does mean, however, that in order to look for the presence of DNA as an indicator of Earth-like life scientists would have to test for the extra bases.
There's obviously a whole lot of other things to consider in the "real" world, notably the metabolism that provides the nucleotides. They made their new letters synthetically but I am sceptical that their "Z", which contains a nitro group, would fit well into purine/pyrimidine biosynthesis.
Basically we know that the existing systems of protein and nucleic acid metabolism must have been optimal at the point of life's origin, and we can argue about whether they could have been replaced later or not, but we are still not really any further forward as to whether under different pre-biotic conditions an alternative metabolism would originate and persist.
However, this work along with others on non-natural amino acids etc are delineating the possible chemical spaces available for that alternative, so maybe one day we will be able to propose a full scheme for "exo-life".
@Spoobistle - "we know that the existing systems of protein and nucleic acid metabolism must have been optimal at the point of life's origin"
Optimal or just lucky? There might be a large number of viable alternate metabolisms, each with a tiny chance of arising in the primordial soup, but the first one to arise and reach the replication stage, wins.
@Allan_George_Dyer I think "lucky" and "optimal" are one and the same in the context of what actually evolved. But if something with 8 base pairs (with or without face-removing-teeth) wants to discuss this calmly with us, well I'm always amenable to a chat over a nice cup of tea.
Why? It's not like it was a race, and all the other types said "Aww man, the 4 letter DNA got lucky first! I'm just giving up and moving back home to work in my father's store!" If there were other viable forms, they would have made an appearance, somewhere. If they were viable, there is absolutely no reason alternate forms would not have appeared.
Basically we know that the existing systems of protein and nucleic acid metabolism must have been optimal at the point of life's origin,
No, that's not how evolution works. We know it was "good enough" to survive more often than whatever it was competing with.
Anybody who thinks evolution produces optimal results has obviously never tried to maintain a human body in working condition for more than a couple decades...
When we're talking DNA/RNA, I'm pretty sure that the first one to be able to reliably duplicate itself using "common stuff in the environment" wins everything.
In the primordial soup, there's plenty of goop for random experiments. However, once the first thing starts to eat the goop, there's less of it.
For two different types of life to compete, they'd have to arise from the goop more or less simultaneously, because otherwise #1 will have eaten everything.
The 3 base pairs can code 64 different combinations. However only 20 different amino acids are used, plus a STOP code, there is plenty of space for more. Most amino acids seem to be specified by the first 2 base pairs of the triplets; but not quite as simple as that.
The trouble is that once established it is very hard to change the assignment of amino acids to combinations - nature will not be able to change to free up a combination to use for something else.
"20 different amino acids are used... there is plenty of space for more."
I believe the official DNA datasheet has them marked as 'reserved for future expansion'.
Currently the unused codons perform a 'halt and catch fire' function, so their use should be avoided.
Actually the code is redundant.
Some amino acids are coded twice or three times by different codons. One (IIRC) is coded only once (not the "stop" codon).
Obviously this means some part of the DNA that cods for a protein (any protein) are much more robust to mutation. A 1 character change does not change the amino acid being coded.
OTOH if it's a part of the molecule that's the amino acid that has only 1 code for it, and that changes....
All that "redundant" code is turning out not to be redundant but can control gene expression and a whole host of other functions. It's part of how different cells can have the same DNA but be very different and it turns out that mutation in the "non-coding" parts of DNA can be more catastrophic than changes to the coding part which as has been noted may include redundancy.
"All that "redundant" code is turning out not to be redundant but can control gene expression and a whole host of other functions."
I think you mean the apparently empty DNA sequences between and even within genes.
The 3 base pair codons provide more combinations than there are entities to be represented. Such an over-provision is also known as redundancy.
"Most amino acids seem to be specified by the first 2 base pairs of the triplets; but not quite as simple as that."
Not quite as simple as the first 2 base pairs aren't enough to specify 20 amino acids and a stop codon. But the way things work by making the third base pair redundant in a lot of cases reduces sensitivity to mutation.
It also suggests that the code as we see it now isn't just the first arrangement that happened by chance as other comments have suggested. It was itself the product of evolution, maybe from a 2 base pair predecessor. Whatever, it requires the evolution of a set of transfer RNAs and their activation enzymes.
There was a paper, damned if I recall where I saw it, just a few days ago which made the case that random mutation in DNA is a feature, not a bug with respect to evolution. Species shifting laterally to another ecosystem being an example. Now whether that is the case, say, on a planet with a tight orbit around a star with flares and such, heck a Wolf-Rayet even, is a valid question. Perhaps then we'd see the advantage of longer base encoding.
Random thought.
"There was a paper, damned if I recall where I saw it, just a few days ago which made the case that random mutation in DNA is a feature, not a bug with respect to evolution."
It's the source of the variations in Darwin's theory. Natural selection works on that. The lethal mutations don't develop at all. The viable ones do and prosper more or less depending on their fitness in the particular environment.
It's common to see a balanced equilibrium of some alleles: an example is s-haemoglobin which helps resist malaria but when homozygous leads to the red blood cells becoming distorted at low blood oxygen levels. The balance point is higher where the risk of malarial infection is higher and the benefits of protection outweigh the risks of sickle cell disease.
This is important news because it shows that DNA analogues can function just as well for information transmission. When humans eventually come across extraterrestrial life forms, whether that's inside this solar system (Europa, Enceladus) or externally (a long time away), the precise composition of the building blocks of those life forms might differ but the underlying nature of the biological processes will be instantly familiar.
When humans eventually come across extraterrestrial life forms, whether that's inside this solar system (Europa, Enceladus) or externally (a long time away), the precise composition of the building blocks of those life forms might differ but the underlying nature of the biological processes will be instantly familiar.
Maybe time for a new "Rule #1": Don't kill anything just for it's DNA as the rest will get really pissed off.
heh
I deliberately left hirigana out because katakana is almost exclusively used for foreign words and therefore (I think) more known outside of Japan. Not to mention the more angular strokes look "cooler" and "futuristic" to westerners, I think. Certainly they have more influence in certain design arenas than hirigana.
I have seen suggestions in print that the first life on Earth (or to arrive here and spread perhaps) may have been based on neither DNA nor RNA but a different, more rad-hard and temperature-insensitive nucleic acid backbone and codons.
RNA life of a sort is around in RNA viruses and it remains possible that there have been two or more changes of the primary nucleic acid system as the Earth changed. It may be that the more durable nucleic acids needed to survive early conditions were energetically or otherwise unsuitable to make evolution possible. There must be some balance between ease of replication, the ability to form long structures that retain their integrity, and the ease of mutation that gives a competitive advantage to organisms that use DNA on Earth.
But if that's right, life on other planets might have gone down the DNA route or might not depending on conditions, and even if they use DNA there's no reason to assume that the same codons result in the same amino acids.
The parallel with computing is obvious.
"The additional four molecules have incredibly long complex chemical names to spell out here", and yet, if the names existed to spell out here, why didn't I see them? Perhaps you meant "The additional four molecules have incredibly long complex chemical names [too long] to spell out here"?
So, these people have "shown" that a DNA variant with eight bases is viable. But I find it more interesting to know which subsets of these eight bases are viable. Obviously, the four-base subset GATC is perfectly viable, but are there other four-base subsets that are viable? And are any in some sense superior to GATC? For example, is there a subset that uses simpler molecules or less energy to replicate? Or some that allow simpler ribosomes? Are there viable two-base subsets?
And what other possible bases are there? Could there be a base that pairs with itself, so you can have a three-base set?
What I never understood about that film:
Presumably Leeloo was humanoid with that special exosuit but is there any real need for aliens to look remotely like us?
Also if we do ever meet aliens it may be that they take on a form similar to us to provide a common frame of reference.
Their actual physical form if they have one may be radically different (cough GalaxyQuest /cough) and also their proteins
may be "backwards" wrt Earth life and use different elements as an oxygen carrier etc.
On the flip side suitably screened food would be a viable trading commodity for those who want to lose weight.
I expect that an alien intelligence based on sentient machines may in fact choose a physical form that is the most
useful in a given environment. The "Nordics" may be of this type if you believe all that stuff.
Also the Roswell Greys aka Asgard probably optimized that form over millions of years.
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