How do start and stop codons regulate translation?

Start and stop codons regulate translation by signalling the beginning and end of protein synthesis, respectively.

In the process of translation, the genetic information stored in the DNA is converted into proteins, which are essential for the functioning of the cell. This process is regulated by specific sequences of nucleotides known as codons. Each codon corresponds to a specific amino acid, which are the building blocks of proteins. The start and stop codons play a crucial role in this process.

The start codon, usually AUG, signals the start of translation. It is the first codon of the messenger RNA (mRNA) to be translated by the ribosome, the cellular machinery responsible for protein synthesis. The AUG codon codes for the amino acid methionine in eukaryotes and a modified methionine (formylmethionine) in prokaryotes. This sets the reading frame for the ribosome, ensuring that the codons are read in the correct groupings.

The stop codons, on the other hand, signal the end of translation. There are three stop codons: UAA, UAG, and UGA. Unlike other codons, stop codons do not code for an amino acid. Instead, they signal the termination of protein synthesis. When the ribosome encounters a stop codon, it releases the newly formed polypeptide chain, and the components of the translation machinery dissociate.

The precise regulation of translation by start and stop codons ensures that proteins are synthesised correctly. Any errors in this process, such as a shift in the reading frame or a premature stop, can lead to the production of non-functional proteins, which can have detrimental effects on the cell. Therefore, the role of start and stop codons in regulating translation is fundamental to cellular function and health.