Coding role #2 1. The second position of a codon: Pyrimidines-hydrophobic amino acids a Purines-polar amino acids 2.If the first two positions are both occupied by G or C each of the four nucleotides in the third position specifies the same amino acid
Coding role #2 1.The second position of a codon: ◼ Pyrimidines-hydrophobic amino acids ◼ Purines-polar amino acids 2.If the first two positions are both occupied by G or C, each of the four nucleotides in the third position specifies the same amino acid
Wobble in the anticodon (反密码子具有摇摆性 Q Question: Is there a specific tRNA for 8 every codon? (If it was true, at least w different tRNAs would exist. r The answer is No B> Some tRNA could recognize several 6 different codons >Inosine is present in the anticodon loop as a fifth base
Wobble in the Anticodon (反密码子具有摇摆性) Question: Is there a specific tRNA for every codon? (If it was true, at least 61 different tRNAs would exist.) The answer is NO ➢ Some tRNA could recognize several different codons ➢ Inosine is present in the anticodon loop as a fifth base The Code Is Degenerate
Inosine H N一H N一H noose N ribose N H H Inosine adenine Inosine arises through enzymatic modification of adenine
Inosine inosine adenine Inosine arises through enzymatic modification of adenine
Wobble concept In 1966, Francis crick devised the wobble concept. It states that the base at the s end of the anticodon is not as spatially confined as the other two allowing it to form hydrogen bonds with more than one bases located at the 3 end of a codon
Wobble Concept In 1966, Francis Crick devised the wobble concept. It states that the base at the 5’ end of the anticodon is not as spatially confined as the other two, allowing it to form hydrogen bonds with more than one bases located at the 3’ end of a codon
Table 15-2 Pairing Combinations with the Wobble concept Base in 5, Anticodon Base in 3 Codon GcA U or A or cGUGc or
Table 15-2 Pairing Combinations with the Wobble Concept Base in 5’ Anticodon Base in 3’ Codon G U or C C G A U U A or G I A, U, or C