Complementary base pairing determines codon-anticodon recognition

Steps:

• Write the anticodon sequences in 5' to 3' direction to match standard codon orientation.
• Find the complementary codon each anticodon recognizes using Watson-Crick rules (A-U, G-C) with wobble only at the third codon position.
• Consult the genetic code table to identify the amino acid for each recognized codon.
• Compare to threonine (codons ACU, ACC, ACA, ACG) to see if other amino acids are specified.

Why B is correct:

• Anticodons 1 and 2 recognize codons outside the ACN group via complementary pairing, coding for non-threonine amino acids per the standard genetic code.

Why the others are wrong:

• A includes anticodons 3 and 4, which recognize threonine codons ACU/ACC/ACA/ACG.
• C includes anticodon 3, which pairs strictly with threonine codons.
• D lists only 3 and 4, both specific to threonine via base pairing rules.

Final answer: B