Final answer:
Codons that differ in either of the first two bases generally require two different tRNA molecules to ensure the correct amino acid is matched for protein synthesis, due to strict base-pairing rules in the first two positions of the codon-anticodon interaction.
Step-by-step explanation:
When an amino acid is specified by several different codons, the codons that differ in either of the first two bases would typically require different tRNA molecules. This is because accurate base pairing is crucial for the first two positions of the codon-anticodon interaction to ensure the correct amino acid is added to the growing polypeptide chain. While there might be some flexibility or "wobble" at the third base position of the codon, changes in the first two bases usually alter the amino acid that is incorporated, necessitating distinct tRNAs that match the codons' first two nucleotides.
Each tRNA molecule has an anticodon arm that is complementary to the mRNA codon and ensures the correct amino acid is brought to the ribosome for protein synthesis. This specificity is due to the strict base-pairing rules where adenine (A) pairs with uracil (U) and cytosine (C) pairs with guanine (G). Should the first two bases of the codon change, the anticodon of the tRNA must change accordingly, usually leading to the requirement for a different tRNA molecule to maintain a proper codon-anticodon match.
Therefore, if codons differ from each other in either of the first two bases, they generally require two different tRNA molecules to bring the appropriate amino acids for protein synthesis. The option 'B' is thus the correct answer to the student's question.