Final answer:
The 3-nucleotide sequence on a tRNA molecule complementary to an mRNA codon is the anticodon, crucial for the specificity in translating proteins.
Step-by-step explanation:
The 3-nucleotide sequence on a tRNA molecule that is complementary to a specific codon on an mRNA molecule is called an anticodon. During the process of translation, each type of tRNA carries a specific amino acid to the ribosome. The anticodon of tRNA pairs with its complementary codon on the mRNA sequence, ensuring the correct sequence of amino acids is translated from the mRNA to create a protein. This pairing is a key part of the Central Dogma which describes how gene sequences are ultimately expressed as proteins.
For example, if an mRNA codon sequence is GCA, which corresponds to the amino acid alanine, the tRNA with the anticodon sequence UGC would bind to it. This specific tRNA would carry alanine to the ribosome for incorporation into the growing polypeptide chain. Understanding this specificity is fundamental in molecular biology, as it is the basis for the genetic code and protein synthesis.