A pharmaceutical researcher develops a new drug that affects bacterial protein synthesis. In an experiment, Escherichia coli is exposed to the drug and serially cultured in media containing tagged nucleotides and amino acids. It is found that the drug inhibits molecules that recognize the highlighted codon in the bacterial mRNA fragment shown in the image below. Which of the following molecules is the most likely target of this drug?

Question

A pharmaceutical researcher develops a new drug that affects bacterial protein synthesis.  In an experiment, Escherichia coli is exposed to the drug and serially cultured in media containing tagged nucleotides and amino acids.  It is found that the drug inhibits molecules that recognize the highlighted codon in the bacterial mRNA fragment shown in the image below.  Which of the following molecules is the most likely target of this drug?

Quizplus · Accepted Answer

There are 64 codons in the genetic code, the majority of which code for amino acids. However, because there are only 20 amino acids, most have more than one codon. For example, GUU, GUC, GUA, and GUG all code for valine. In addition, there are codons that call for initiation or termination of protein synthesis. The universal start codon is AUG, which codes for methionine. UAA, UAG, and UGA are stop codons, which do not code for amino acids or bind tRNA. Instead, when the ribosome encounters a stop codon, releasing factor proteins bind to the ribosome and stimulate release of the formed polypeptide chain and dissolution of the ribosome-mRNA complex. (Choice A) Charged tRNA delivers amino acids to the protein synthesis complex. The anticodon on a tRNA molecule recognizes the corresponding codon on mRNA, assuring proper amino acid sequencing. (Choice B) Elongation factors facilitate tRNA binding and the translocation steps of protein synthesis. (Choice D) Transcription produces a pre-mRNA molecule containing both introns and exons. Splicing is a post-transcriptional modification in which introns are removed from pre-mRNA via small nuclear ribonucleoproteins (snRNPs). (Choice E) Initiation of gene transcription is governed by the binding of transcription factors to the regulatory region of the gene. Transcription factor II D binds to the TATA promoter sequence located ~25 bases upstream from the coding region of the gene. (Choice F) During protein synthesis, uncharged tRNA (lacking an amino acid) does not interact with mRNA and ribosomes. Educational objective: Releasing factors recognize stop codons (eg, UAA, UAG, and UGA) and terminate protein synthesis. They facilitate release of the polypeptide chain from the ribosome and dissolution of the ribosome-mRNA complex. __________ References: Terminating eukaryote translation: domain 1 of release factor eRF1 functions in stop codon recognition. (http://www.ncbi.nlm.nih.gov/pubmed/10999601) Two-step model of stop codon recognition by eukaryotic release factor eRF1. (http://www.ncbi.nlm.nih.gov/pubmed/23435318)

A Pharmaceutical Researcher Develops a New Drug That Affects Bacterial