Final answer:
The initiator tRNA occupies the P site on the ribosome during translation initiation, while all subsequent tRNAs enter the A site.
Step-by-step explanation:
The student's question pertains to the process of translation initiation in protein synthesis. In this process, the initiator tRNA immediately occupies the P (peptidyl) site on the ribosome, which is the only site to which it can bind initially. This happens thanks to the help from other proteins forming the initiation complex. In contrast, all subsequent tRNAs first enter the A (aminoacyl) site. After the small ribosomal subunit has located the AUG start codon on the mRNA, translation initiation begins when the large subunit attaches, allowing the initiator tRNA, carrying methionine (Met), to bind to the P site. This sets the stage for the incoming aminoacyl tRNAs, which will carry the respective amino acids corresponding to the codons following the AUG, to enter the A site, where they will contribute to the elongating polypeptide chain.