Question

A codon that specifies leucine undergoes a single-base substitution, producing a new codon that specifies methionine. The codons that specify leucine are UUA, UUG, CUU, CUC, CUA, and CUG. The only codon that specifies methionine is AUG. Which of the following correctly describes the mutation?

A transition at the third nucleotide position of a leucine codon

A transversion at the first nucleotide position of a leucine codon

A transversion at the third nucleotide position of a leucine codon

A transition at the first nucleotide position of one of the leucine codons

A transversion at the second nucleotide position on a leucine codon

Answer 1

The mutation is a transversion at the first nucleotide position of the leucine codon CUG, resulting in the methionine codon AUG.

Step-by-step explanation:

The consequence of a single-base substitution in a codon that specifies leucine, producing a codon that specifies methionine. Since the methionine codon is AUG, the only leucine codon that can change in the first position to create this is CUG. Changing the C to an A through a single-base substitution will result in AUG, the codon for methionine. This type of mutation is known as a transversion, where a purine is replaced by a pyrimidine or vice versa. Since C (a pyrimidine) is being replaced by A (a purine), it is a transversion occurring at the first nucleotide position of the leucine codon.