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Wobble hypothesis.How does met & trp not get mis translated?

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Wobble hypothesis.How does met & trp not get mis translated?

Postby Awol » Sun Apr 08, 2012 6:33 pm

I understand the principle of the wobble hypothesis, that the last base pair between a mRNA codon and a tRNA anticodon is not as stringent as the DNA base pairing rules. However the rules as they were explained to me do not compensate for met & trp.

If the tryptophan codon = (5'-UGG-3') then the anticodon according to these rules could be
(3'-ACU-5') or (3'-ACC-5'). But the stop codon (5'-UGA-3') can then also pair with (3'-ACU-5') according to these rules?

The same would be true for methionine codon (5'-AUG-3') it can pair with the
anticodon (3'-UAU-5'), but this anticodon is also able to bind with Isoleucine (5'-AUA-3')?

Rules of Wobble hypothesis: (as they were explained to me, included here incase incorrect).
(3rd base of codon: left) can pair with (1st base of anticodon: right)
(A or G) pairs with (U)
(G) pairs with (C)
(C or U) pairs with (G)
(U, C or A) pairs with (I)
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Postby Sue4 » Tue Apr 10, 2012 4:30 pm

You seem to have a misunderstanding about this. Among the 64 possible codons, 61 codons specify amino acids (except the 3 stop codons). If each tRNA molecule pairs with its complementary codon using Watson-Crick base pairing, then 61 different tRNA molecules would be required. But some tRNA molecules can recognize more than one codon due to Wobble base pairing and thus the number of tRNA molecules found in a cell is less than 61. This is the advantage of Wobble base pairing. Hence, there can be more than one codon that specify the same amino acid. But there are no several tRNA molecules that recognize the same codon.
Tryptophan is coded only by UGG and methionine is coded only by AUG. So Trp codon is recognized by the tRNA with the anticodon ACC and Met codon is recognized by the tRNA with the anticodon UAC. There is no any tRNA with the anticodon ACU.
As an example for Wobble base pairing, we can consider the amino acid Tyrosine. It is coded by two codons, UAU and UAC. Both of these codons can be identified by the same tRNA molecule. The 5' base of the anticodon of this tRNA is G. It can pair with both C and U due to Wobble base pairing and thus can identify both codons that code Tyrosine.
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Postby Awol » Wed Apr 11, 2012 3:28 pm

This makes a lot more sense to me now. My reasoning was that there was 61 different aminoacyl-tRNAs in the cell i see know how i why i was getting confused. Thank you for taking the time to explain this to me.
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