How does a stop codon terminate translation?

A stop codon terminates translation by signalling to the ribosome to end the protein synthesis process.

In the process of translation, the genetic information in the form of mRNA is converted into a sequence of amino acids to form a protein. This process takes place in the ribosome, a cellular machinery that reads the mRNA sequence and assembles the corresponding amino acids. The mRNA sequence is read in groups of three nucleotides, known as codons. Each codon corresponds to a specific amino acid or a signal to start or stop the translation process.

The stop codon plays a crucial role in this process. There are three stop codons: UAA, UAG, and UGA. When the ribosome encounters a stop codon, it recognises this as a signal to terminate the translation process. This is facilitated by release factors, proteins that recognise the stop codon and promote the release of the newly synthesised polypeptide chain from the ribosome.

The stop codon does not code for an amino acid, unlike other codons. Instead, it signals the end of the protein-coding sequence. This ensures that the protein is synthesised correctly, with the right sequence of amino acids. If a stop codon is missing or misplaced, it can result in a protein that is too long or too short, which can have serious consequences for the cell.

In summary, the stop codon is a vital part of the translation process. It signals to the ribosome to end the protein synthesis process, ensuring that the protein is of the correct length and sequence. This is facilitated by release factors, which recognise the stop codon and promote the release of the newly synthesised protein. Without the stop codon, proteins could be synthesised incorrectly, potentially leading to cellular dysfunction.