A group of three bases on a tRNA molecule that are complementary to an mRNA codon is known as the:

• A. Anticodon
• B. Codon
• C. Introns
• D. Exon

Answer: (A)

During translation, the tRNA that brings in an amino acid carries a three-nucleotide sequence called the anticodon. This anticodon pairs with a complementary three-nucleotide codon on the mRNA, guiding the ribosome to add the correct amino acid to the growing protein. The anticodon is the part of tRNA that ensures the genetic code is read accurately by matching its bases to the codon’s bases (A pairs with U, G with C, with some flexibility at the third position known as wobble). The other terms describe different things: a codon is the three bases on mRNA itself, while introns and exons are parts of a gene's transcript (with introns removed and exons encoding the protein). Therefore, the three bases on tRNA that are complementary to an mRNA codon are the anticodon.