Final answer:
The structure responsible for delivering amino acids during protein synthesis is the transfer RNA (tRNA), which matches its anticodon to the mRNA codon to add the correct amino acid to the polypeptide chain.
Step-by-step explanation:
The structure responsible for bringing in the amino acids during protein synthesis is the transfer RNA (tRNA). Each tRNA molecule carries a specific amino acid to the ribosome, where proteins are assembled. The anticodon of the tRNA pairs with the complementary codon on the messenger RNA (mRNA) sequence, ensuring that the correct amino acid is added to the growing polypeptide chain. When looking at the question options (A. 1, B. 2, C. 3, D. 4), it's clear that specific structures are not listed. However, tRNA would be the correct answer if it were one of the options provided. To answer question 22, an RNA molecule requires three letters (a codon) to code for a single amino acid.