alleryStart learning →Which ribosomal site does the initiator tRNA occupy as the initiation complex forms?
AThe P site, entered directly
BThe A site, entered directly
CThe E site, entered directly
DThe A site, then the P site
Answer & Solution
Correct answer: A. The P site, entered directly
1. Every other charged tRNA enters at the A site and only later shifts to the P site.
2. The initiator tRNA is the exception and binds directly to the P site.
3. This holds for the prokaryotic initiator carrying formylated methionine and for the eukaryotic initiator as well.
4. Entering the P site directly leaves the A site free from the start.
5. That free A site is ready to accept the tRNA for the first codon after the AUG.
6. The E site only ever releases spent tRNAs, so nothing enters translation there.
_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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