Which base of a codon is called wobble base?

Concept-

• The genetic code term is given by George Gamow.
• mRNA contains code for each amino acid and it is called a codon.
• There are four types of N₂ base in m-RNA (A, U, G, C) for amino acids.
• The genetic code is triplet i.e. one codon consists of three nitrogen bases.

Explanation-

• There are 64 codons for 20 types of amino acids.
• So some amino acids are coded by more than one codon, hence the code is degenerate.
• Single amino acid coded by more than one codon is called "Degeneracy of genetic material".
• Example-
  • Leucine = CUU, CUC, CUA, CUG, UUA, and UUG.
  • Serine = UCU, UCC, UCA, UCG, AGU, and AGC.
• Degeneracy of genetic code increases the efficiency of protein synthesis.
• Degeneracy of genetic code is related to the third position (3' - end of triplet codon) of the codon.

Thereby the third base is described as a "Wobbly base".

Additional Information

• Nonsense codons do not specify any amino acid. 
• A nonsense codon is UAA, UAG, and UGA.