tRNA Function—Anticodon Binding Partner During translation, the anticodon loop of a tRNA specifically base-pairs with which sequence?

Introduction / Context:
Accurate decoding during translation relies on complementary base pairing between the three-nucleotide anticodon of tRNA and the three-nucleotide codon on mRNA. This pairing ensures the correct amino acid is incorporated into the growing polypeptide chain at each step of elongation.

Given Data / Assumptions:

• tRNAs are aminoacylated with specific amino acids by aminoacyl-tRNA synthetases.
• The anticodon positions the tRNA on the mRNA in the ribosome A site.
• Initiation signals (Shine–Dalgarno in prokaryotes, Kozak in eukaryotes) are separate elements and not the anticodon target.

Concept / Approach:
Identify the direct base-pairing partner of the anticodon. While rRNA forms the structural core of the ribosome and recognizes the Shine–Dalgarno sequence via 16S rRNA, the anticodon itself pairs with the mRNA codon within the decoding center to maintain reading frame and fidelity.

Step-by-Step Solution:

Verification / Alternative check:
Structural snapshots of the ribosome show the anticodon loop hydrogen-bonded to the codon triplet in the 30S/40S decoding center.

Why Other Options Are Wrong:

• rRNA: contacts tRNA elsewhere but is not the anticodon's base-pairing target.
• Amino acid: attaches at the tRNA 3' end, not at the anticodon.
• Shine–Dalgarno/Kozak: ribosome positioning signals, not anticodon pairing sites.

Common Pitfalls:
Confusing ribosome–mRNA alignment signals with anticodon–codon pairing; they are distinct steps.

Final Answer:
An mRNA codon