What is the three-base sequence of nucleotides in mRNA called?

• A. Anticodon
• B. mRNA
• C. tRNA
• D. Codons

Answer: (D)

The three-base sequence in messenger RNA that specifies an amino acid is called a codon. Each codon consists of three nucleotides and the set of codons forms the genetic code that directs which amino acids are added to a growing protein chain. During translation, the ribosome reads mRNA codons one triplet at a time and matches each with the corresponding anticodon on tRNA to bring in the correct amino acid. The other options describe different things: an anticodon is the three-base sequence on tRNA that pairs with a codon, mRNA is the molecule that carries the code, and tRNA is the adaptor molecule that brings amino acids. So the unit on mRNA that encodes a specific instruction is the codon.