A researcher develops 2 functional mRNA sequences composed of CUC and CUU trinucleotide repeats, respectively. He subsequently incubates these mRNAs in a solution containing functional ribosomes and tRNAs charged with the appropriate amino acids. After several hours, it is found that both mRNA sequences produce polypeptide chains containing leucine repeats. This observed finding is due to which of the following genetic principles?

Question

A researcher develops 2 functional mRNA sequences composed of CUC and CUU trinucleotide repeats, respectively.  He subsequently incubates these mRNAs in a solution containing functional ribosomes and tRNAs charged with the appropriate amino acids.  After several hours, it is found that both mRNA sequences produce polypeptide chains containing leucine repeats.  This observed finding is due to which of the following genetic principles?

Quizplus · Accepted Answer

11ec160b_3773_7e9e_9249_3df84934a036_MD0001_00 There are 61 codons that code for amino acids, but only 20 amino acids are used in protein synthesis. The genetic code is therefore considered "degenerate" because more than 1 codon can code for a particular amino acid. For instance, the codons CUC and CUU both code for the amino acid leucine. Individual tRNA molecules are specific for certain amino acids and recognize the mRNA codons associated with those amino acids. Certain tRNA molecules can recognize multiple different codons coding for the same amino acid, a phenomenon explained by the wobble hypothesis. This hypothesis states that the first 2 nucleotide positions on the mRNA codon require traditional (Watson-Crick) base pairing with their complementary nucleotides on tRNA, whereas the third "wobble" nucleotide position may undergo less stringent (nontraditional) base pairing. In the case of leucine, for example, 1 tRNA molecule recognizes 2 codons (CUC and CUU) because only the first 2 nucleotide positions (CU in the codon) form traditional bonds. (Choice A) The genetic code is not ambiguous as each codon is associated with only a single amino acid. (Choice B) The genetic code is read sequentially from a starting point and has no internal punctuation as each codon is adjacent to the next without spacer nucleotides in between. (Choice C) Genetic transition refers to a point mutation that results in replacement of a purine nucleotide for another purine or a pyrimidine nucleotide for another pyrimidine. In contrast, transversion refers to a point mutation that results in the replacement of a purine nucleotide for a pyrimidine or a pyrimidine nucleotide for a purine. (Choice D) The genetic code is almost universal as amino acid codons are nearly identical across species; however, mitochondria and some bacteria and single-celled eukaryotes deviate from the standard genetic code. Educational objective: The genetic code is considered "degenerate" because more than 1 codon can code for a particular amino acid. Some of this degeneracy is explained by the wobble hypothesis, which states that the first 2 nucleotide positions on the mRNA codon require traditional (Watson-Crick) base pairing, whereas the third "wobble" nucleotide position may undergo less stringent (nontraditional) base pairing. __________ References: tRNA's wobble decoding of the genome: 40 years of modification. (http://www.ncbi.nlm.nih.gov/pubmed/17187822)

A Researcher Develops 2 Functional MRNA Sequences Composed of CUC