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Originally Posted by eburacum45
As far as xenobiology is concerned, I think Huevos Grandes might be wrong; on our world twenty amino acids are coded for in DNA; but more that a hundred different amino acids have been discovered, some only in meteorites (carbonaceous chondrites), and apparently there might be billions of possible examples.
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I don't need "Xenobiology" to be correct, in this instance; regular biology will suffice. You fall into the same trap as the author, making mysterious this prospect that other-worldly amino acids can form new and exciting lifeforms. This is bunk- most complex lifeforms on Earth do
not build 20 amino acids (this is one of the reasons I eat
food).
In reality, it is not only amino, but
imine acids that go into creating proteins, and nature favors simplicity. Other amino acids do go into forming protein secondary and tertiary structures, but are irrelevant, because even minute differences in the 'R' chain into something that won't form bonds to create secondary- and tertiary structures (e.g. a synthetase enzyme with 38 acids "folded", bonded acids will not work properly if say- one of the glutamic acids has a oxygen atom or two replaced by a copper). Other amino acids are possible, sure- but not necessarily ones that work. Amino acids are the basic building blocks because they are basic- not some randomized "Earth" chance.
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Originally Posted by eburacum45
On our world the evolution of RNA and DNA replication obviously caused the selection of lifeforms containing these twenty acids.
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Obviously not. I would ask for your explanation for this, using basic biochemistry, referring to my analysis above.
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Originally Posted by eburacum45
But before self-replication emerged, life-like organic processes must have existed for an unknown time; we might find worlds where self-replication through DNA never evolves, and on those worlds the many other possible amino acids might be found. It may even be the case that other forms of self replication might emerge, not using RNA/DNA at all;
such life, if possible, could potentially utilise many amino acids not used on Earth.
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Again- chemistry doesn't restrict itself to borders in this manner. The same elements that make aspartic acid and
amino acid X possible on Ceti Alpha 5 (Khaaaaaaan!), for example, are available on Earth. And while I am unable to disprove your assertion, I will say that complex life can only form where DNA/RNA (other some other
stable information-carrying molecule) self-replicates. Before enclosed membranes, organelles, and concentrated agglomerations of nutrients could be counted upon by the DNA/RNA, floating freely in the "soup" of Precambrian life, replication happened by chance. Mutation was abundant, and almost invariably caused problems, rather than improvement.
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Originally Posted by eburacum45
I don't think that anything we know currently can rule this possibility out, but by all means prove me wrong.
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You can make "new" amino acids at home. Your own body is creating them all the time. They simply just don't tend to make working proteins, are are thus destroyed. Ask a biochemist sometime how many potential R-chains a protein can have.