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Yet *another* evolution thr...

Raven
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SubjectYet *another* evolution thread; was: Queen mother (of Britain) has died
FromRaven
Date2002-04-11 00:30 (2002-04-11 00:30)
Message-ID<563t8.1266$Rd4.3889@news.get2net.dk>
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Newsgroupsalt.fan.tolkien
FollowsJoy
FollowupsTamim (57m) > Raven
"Joy" <queen_yoj@hotmail.com>skrev i en meddelelse news:29ff3ad6.0204092110.3d666053@posting.google.com...

Joy
It has been calculated that the odds of a spontaneous formation of even a small protein, given *100 billion years* (10 to 20 times greater than the approximated age of the earth) is less than 1 to 10 to the 60th.

These are the odds that a specific protein forms spontaneously. But take the example I mentioned in the post I made about eyes. The protein that we humans have in our retinas, without which our retinas could not detect light, is called opsine. When it's dark, the opsine couples with a smaller molecule that is produced from vitamin A, forming rhodopsine. When light is shone upon rhodopsine, that smaller molecule changes shape and therefore it detaches from the protein. This triggers a nerve signal through the optic nerve to your brain. The odds that, if you randomly put amino acids together, you would by chance produce modern opsine, are slim indeed. But the earliest organisms with the ability to sense light quite certainly didn't use modern opsine. Any peptide would do, so long as it either directly or coupled with another, already existing molecule, could change its shape when illuminated. Perhaps a very short one. If there are potentially 10^50 amino acid sequences that would become a protein capable of detecting light, and all in all 10^60 different peptides of a reasonably short length, then the odds of producing a light-sensitive peptide by chance in any one try becomes much higher: one to ten billion. Make a random peptide a thousand billion times, and you can't avoid producing a light-sensitive peptide. Once you have a short, crude, but working rudimentary "opsine", it can evolve into a more efficient opsine.

And where is DNA from? I find the complexity of DNA mind-boggling.

Same thing. The basic mechanism of life is that you have two kinds of RNA, mRNA which is a long strand of RNA, and tRNA, which is RNA that has bunched up into roughly a ball like a small ball of yarn. tRNA can attach itself to amino acids, and the shape of the tRNA determines which amino acid it attaches itself to. mRNA can attach to tRNA, and therefore a strand of mRNA can form the blueprint for a peptide: the sequence of nucleotides in a strand of mRNA corresponds to a sequence of amino acids in a peptide. But a number of enzymes are needed to make it all happen. You may call tRNA an enzyme if you will, but real enzymes are also needed in any living cell. In most living organisms the mRNA is itself copied off DNA, which is more stable and acts as the basic blueprint. But some very simple organisms have no DNA, only RNA. Some viruses, including the HIV virus which causes AIDS, have only RNA, but produce an enzyme called "reverse transcriptase" that can produce DNA off an mRNA blueprint - the opposite of what normally goes on in cells.

Imagine an original soup in which there are amino acids and nucleotides - both DNA and RNA are made up from nucleotides, and both amino acids and nucleotides have been produced from simple molecules in the lab under conditions mimicking what we imagine they were on the early Earth. Imagine that the nucleotides form strands of RNA. Some of these will bunch up into tRNA, while others remain unfolded, and are less stable - they break up into individual nucleotides more easily. RNA does have a weak self-catalytic effect, so that mRNA strands may replicate crudely and produce peptides even if there aren't any real enzymes yet. All that it takes to start life in this original soup is that one randomly formed strand of mRNA produces a peptide that can catalyze RNA in some way that helps it to duplicate itself. Perhaps the new peptide protects mRNA without hampering it when it duplicates itself, perhaps it catalyzes the duplication of mRNA. This is the beginning of life: a rudimentary organism that still consists only of an mRNA string that can duplicate itself more efficiently. The rest is evolution: mutation followed by natural selection.

Jon L. Beck.

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Tamim (57m) > Raven