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Wobble in the Genetic Code

According to the genetic code, the cell would need tRNAs with 61 different anticodons to complement the available 61 codons. However, due to the degeneracy of the genetic code, the third base is less discriminatory for the amino acid than the other two bases. This third position in the codon is referred to as the wobble position. At this position Us and Cs may be read by a G in the anticodon. Similarly, As and Gs may be read by a U or y (pseudouridine) in the anticodon.

The tRNAs also contain a series of unusual modified nucleotides. One of these nucleotides is inosine (I). If the tRNA contains an I in the anticodon at the wobble position, this tRNA may read codons having As, Us or Cs in the third position.


Nucleotide
at 5' end of
anticodon
Nucleotide
at 3' end of
anticodon
G > U or C
C > G
A > U
U > A or G
I (indosine) > A, U or C

Amino acids with one codon
AUG UGG
Met Trp
Amino acids with two codons
AAA
AAG
AAC
AAU
CAA
CAG
CAC
CAU
GAA
GAG
Lys Asn Gln His Glu
GAC
GAU
UAC
UAU
UGC
UGU
UUC
UUU
Asp Tyr Cys Phe
Amino acids with three codons
AUA
AUC
AUU
Ile
Amino acids with four codons
ACA
ACC
ACG
ACU
CCA
CCC
CCG
CCU
GCA
GCC
GCG
GCU
GGA
GGC
GGG
GGU
GUA
GUC
GUG
GUU
Thr Pro Ala Gly Val
Amino acids with six codons
CGA  AGA
CGC  AGG
CGG
CGU
CUA  UUA
CUC  UUG
CUG
CUUU
UCA  AGC
UCC  AGU
UCG
UCU
Arg Leu Ser

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