What factor most directly ensures that the correct amino acid is added to a polypeptide chain during protein synthesis?

The correct answer highlights the role of transfer RNA (tRNA) in ensuring that the appropriate amino acid is incorporated into the growing polypeptide chain during protein synthesis. Each tRNA molecule is equipped with a specific anticodon that is complementary to a codon in the messenger RNA (mRNA). This complementary pairing is essential, as it allows the tRNA to recognize and bind to the corresponding codon on the mRNA strand. Each type of tRNA is associated with a specific amino acid, meaning that the correct amino acid will only be added to the polypeptide chain if the right tRNA is present. Consequently, the precision of this process is critical for the proper translation of genetic information into functional proteins.

Other factors listed, such as ribosomes, are important for the overall process of translation but do not directly determine the specificity of the amino acid being added. The presence of a single amino acid for all proteins does not occur; proteins are composed of a variety of amino acids, each dictated by distinct codons on the mRNA. Interaction between mRNA and DNA is crucial for transcription, but it does not directly pertain to the addition of amino acids during translation. Therefore, the specificity conferred by the unique pairing of tRNA antic