alleryStart learning →Tetracycline blocks the A site of a bacterial ribosome. Which step does that stop?
AAssembly of the two ribosomal subunits
BTransfer of the chain to the next residue
CBinding of charged tRNAs to the ribosome
DRecognition of a nonsense codon at the end
Answer & Solution
Correct answer: C. Binding of charged tRNAs to the ribosome
1. The A site is where incoming charged aminoacyl tRNAs bind.
2. Blocking that site therefore stops tRNAs from binding to the ribosome.
3. With no tRNA delivered, no codon after the start can be read and elongation never gets going.
4. Chloramphenicol is the drug that blocks peptidyl transfer, so growth of the chain is the effect of that antibiotic instead.
5. Subunit assembly happens before the A site is used, so it proceeds unhindered.
6. Termination needs a chain to release, so it is never reached rather than being the step blocked.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 15 "Genes and Proteins", section 15.5 Ribosomes and Protein Synthesis_
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