The Antibiotic Streptomycin Binds to the 30S Subunit in Bacteria

question 45

Essay

The antibiotic streptomycin binds to the 30S subunit in bacteria and interferes with translation. Streptomycin resistance (SmR) can occur through mutation in the rpsL gene, which encodes the ribosomal protein S12. The antibiotic can no longer bind to the altered protein, so translation can occur without interference from the antibiotic. However, in the absence of streptomycin, many SmR strains of bacteria grow less well than the non-mutant streptomycin-sensitive (SmS) bacteria.
a. Propose a model for why SmR bacteria grow better than SmS bacteria in the presence of streptomycin but not as well in the absence of streptomycin.
b. During translation, an incorrect amino acid is occasionally incorporated into the polypeptide chain-that is, the amino acid added does not correspond to the codon at that location in the mRNA. You develop an assay that can assess this rate of incorrect amino acid incorporation and thereby estimate the accuracy of translation in bacteria. You find that SmR bacteria are more accurate than SmS bacteria in this experiment. How might this observation affect your model above?

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