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An Argument Against Intelligent Design
Feb. 21st, 2012 08:57 pmToday, I began the third week-long shortcourse; this one is on translational machinery. And also, there was a quite fantastic thing to show how there is no intelligent creator.
The basis of the thing is in tRNAs. These shuttle amino acids along and allow the ribosomes to place a specific one into a growing protein. It recognizes which tRNA it needs using codon-anticodon complimentarity with the mRNA. So far, so simple.
But a three-base codon give sixty-four possible combinations. Even if you use use four of them to say STOP, that's still three times the number of needed codons. So some amino acids have more than one codon. This does not work out to three per amino acid, though; some have four and some have two. The reason is because it allows the third base pair to be "wobbly;" what is there does not matter quite as much as that it is always a purine (A or G) or a pyrimidine (U or C). This wobbly is good, since it means that if the ribosome makes a mistake matching the tRNA, it is less likely to affect the protein.
Then there is the strange case of Isoleucine and Methionine. Methionine is the amino acid that is always the one at the beginning of the protein - the Met codon is also the symbol for "begin!" It is AUG. AUX, where X is A, T, or C, means isoleucine instead. This means that the the ribosome absolutely cannot make a mistake in finding AUG versus AUX, or the protein doesn't start right.
Fortunately, there is the sugar inosine, which we show with I. I is a weird sugar, in that it can pair with A or T or U, but never G. It is made from A by a fairly simple reaction, and it is in fact how the body breaks down adenosine to become uric acid. So an intelligent designer would go, "Ah, the tRNA for isoleucine will have the anticodon TGI, and be able to pair with any AUX that is not AUG." And in fact when I was asked this in class today, this was my answer. It was a good answer, and my teacher went, "Huh. I like that." Is this how it actually works, though?
Of course not.
Instead, biology does the very strange thing of modifying the last base of the Met anticodon, so that instead of being TGC it becomes TG(k2)C. This somehow prevents the ribosome from ever putting the wrong tRNA in there, though mechanisms currently unknown. It is expensive, because instead of using a protein that already hangs around to digest A, there has to be another protein that does the C->(k2)C modification. It is inelegant. It reeks of a quick cludge to fix a problem after the fact.
It is, in short, another argument against intelligent design.
The basis of the thing is in tRNAs. These shuttle amino acids along and allow the ribosomes to place a specific one into a growing protein. It recognizes which tRNA it needs using codon-anticodon complimentarity with the mRNA. So far, so simple.
But a three-base codon give sixty-four possible combinations. Even if you use use four of them to say STOP, that's still three times the number of needed codons. So some amino acids have more than one codon. This does not work out to three per amino acid, though; some have four and some have two. The reason is because it allows the third base pair to be "wobbly;" what is there does not matter quite as much as that it is always a purine (A or G) or a pyrimidine (U or C). This wobbly is good, since it means that if the ribosome makes a mistake matching the tRNA, it is less likely to affect the protein.
Then there is the strange case of Isoleucine and Methionine. Methionine is the amino acid that is always the one at the beginning of the protein - the Met codon is also the symbol for "begin!" It is AUG. AUX, where X is A, T, or C, means isoleucine instead. This means that the the ribosome absolutely cannot make a mistake in finding AUG versus AUX, or the protein doesn't start right.
Fortunately, there is the sugar inosine, which we show with I. I is a weird sugar, in that it can pair with A or T or U, but never G. It is made from A by a fairly simple reaction, and it is in fact how the body breaks down adenosine to become uric acid. So an intelligent designer would go, "Ah, the tRNA for isoleucine will have the anticodon TGI, and be able to pair with any AUX that is not AUG." And in fact when I was asked this in class today, this was my answer. It was a good answer, and my teacher went, "Huh. I like that." Is this how it actually works, though?
Of course not.
Instead, biology does the very strange thing of modifying the last base of the Met anticodon, so that instead of being TGC it becomes TG(k2)C. This somehow prevents the ribosome from ever putting the wrong tRNA in there, though mechanisms currently unknown. It is expensive, because instead of using a protein that already hangs around to digest A, there has to be another protein that does the C->(k2)C modification. It is inelegant. It reeks of a quick cludge to fix a problem after the fact.
It is, in short, another argument against intelligent design.
