W OBBLE P ROBLEMS WOBBLE RULES for codon-anticodon pairing Simple rules govern pairing between a codon (in mRNA) and the anti-codon (in tRNA). 1. As for all nucleic acids, pairing is antiparallel ---- a 5’ to 3’ sequence in the codon pairs with a complement (in the anticodon) aligned 3’ to 5’. 2. As for all nucleic acids, a purine always pairs with a pyrimidine and Adenine pairs with Uracil (Thymine in DNA) Guanine pairs with Cytosine. 3. The only novelty is that for tRNA/codon pairing G-U pairs (and U-G pairs) are permitted in the third position (3’ end) of the codon. That is, the anti-codon 3’ GUG 5’ can pair with codon 5’ CAU 3’ as well as 5’ CAC 3’ (G in anticodon reads both U and C in codon) but the anti-codon 3’ GUA 5’ can pair only with codon 5’ CAU 3’ (A in anticodon can’t wobble -- reads only U) Notice, there is no anticodon that can pair uniquely with codon 5’ CAC 3’.
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