Codon vs. Anticodon — What's the Difference?

Codons are essential elements in the genetic code, found within messenger RNA (mRNA). Each codon consists of three nucleotides, and it specifies either one of the twenty amino acids used in the synthesis of proteins or a stop signal, indicating the end of protein synthesis. In contrast, anticodons are found in transfer RNA (tRNA) and play a critical role in translating the mRNA's genetic information into proteins. An anticodon is a set of three nucleotides that are complementary to an mRNA codon, allowing tRNA molecules to bring the correct amino acid to the ribosome during protein synthesis.

While codons are integral to the process of transcription, where DNA is converted into mRNA, anticodons are central to translation, the next step where the sequence of mRNA is decoded to produce proteins. Codons are thus a part of the language that dictates how genetic information is expressed, whereas anticodons are part of the machinery that interprets and carries out the instructions encoded in mRNA.

The specificity of the codon-anticodon pairing is crucial for the accuracy of protein synthesis. A codon in an mRNA molecule will only pair with the anticodon of a tRNA molecule that carries the appropriate amino acid. This specificity ensures that proteins are assembled correctly according to the genetic instructions. For instance, the codon AUG not only codes for the amino acid methionine but also serves as the start signal for protein synthesis, whereas anticodons, being complementary, ensure the start of the protein assembly with the correct amino acid.

The interaction between codons and anticodons is facilitated by the ribosome, a complex molecular machine. The ribosome ensures that codons and anticodons pair correctly, enabling the tRNA to deliver the appropriate amino acid to the growing polypeptide chain. This stepwise addition of amino acids leads to the formation of a protein with a specific sequence, dictated by the sequence of codons in the mRNA.

Both codons and anticodons are fundamental to the process of gene expression, playing roles in different but interconnected stages of protein synthesis. Without the precise matching of codons and anticodons, the accurate translation of genetic information into functional proteins could not occur, highlighting the importance of both elements in the central dogma of molecular biology.