One particular codon codes only for one amino acid, but an amino acid can be coded for by several different codons. Now according to the genetic code, the codon UUU codes for the amino acid phenylalanine and UUA codes for leucine. But, according to the Wobble Hypothesis, the base on the third position of the codon and that on the anticodon need not be complementary (which helps explain why there are very few types of tRNA molecules, inspite of there being 61 codons). If this hypothesis is true, then we could have a phenylalanine placed in a position which was meant to be for leucine, and vice versa (since the codons coding for them differ only in their third base). The same holds true for pairs like aspartic acid & glutamic acid and serine & arginine. So how does translation of a particular mRNA molecule result in the right polypeptide sequence?
Answer
Wobble pairing is just a phenomenon and not a hard and fast rule. There are some justifications for why it should exist and that is why it is still called a hypothesis. And this statement is not true:"the base on the third position of the codon and that on the anticodon need not be complementary". The anticodon residue corresponding to the third residue of codon can be a promiscuous base which can pair with two or many different bases. The tRNA for Phenylalanine has an anticodon - GAA which can pair with both UUU and UUC but not UUA.
So the statement of wobble hypothesis is that the first base of the anticodon (often is a modified/atypical nucleobase) can show promiscuity of binding.
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