Stop codon

Definition

A stop codon is a nucleotide triplet in messenger RNA (mRNA) that signals the termination of protein synthesis during translation. These codons do not code for any amino acids and are essential for ensuring that proteins are synthesized correctly by marking the end of the polypeptide chain, allowing ribosomes to release the newly formed protein.

5 Must Know Facts For Your Next Test

1. There are three stop codons in the genetic code: UAA, UAG, and UGA.
2. Stop codons play a critical role in ensuring that proteins are synthesized to their proper length, preventing incomplete or dysfunctional proteins.
3. When a ribosome encounters a stop codon during translation, it triggers the release of the polypeptide chain and disassembles the translation machinery.
4. The presence of a stop codon in mRNA does not correspond to an amino acid, which distinguishes them from other codons that code for specific amino acids.
5. Mutations that change a regular codon into a stop codon can lead to premature termination of protein synthesis, which can result in genetic disorders or diseases.

Review Questions

• How do stop codons contribute to the process of translation in protein synthesis?
  • Stop codons are crucial for completing the process of translation by signaling the ribosome to halt protein synthesis. When the ribosome reads a stop codon in the mRNA sequence, it prompts the release of the completed polypeptide chain and dissociation of the ribosomal subunits. This ensures that proteins are synthesized accurately and prevents them from being excessively long or improperly folded.
• Compare and contrast stop codons with start codons in terms of their roles in translation.
  • Start codons and stop codons both play vital roles in translation but serve opposite functions. A start codon, typically AUG, marks the beginning of protein synthesis by signaling where translation should commence, while stop codons—UAA, UAG, and UGA—indicate where translation should end. Together, they ensure that proteins are synthesized correctly from start to finish.
• Evaluate the potential impacts of mutations that convert regular codons into stop codons on protein function and organism health.
  • Mutations that transform regular codons into stop codons can lead to premature termination of protein synthesis, resulting in truncated proteins that may lack essential functional domains. This can significantly impair protein function and contribute to various genetic disorders or diseases. Such mutations can disrupt cellular processes, leading to broader health implications for the organism, including developmental issues or increased susceptibility to certain conditions.

Related terms

start codon: A start codon is a specific nucleotide sequence, usually AUG, that initiates translation and signals the start of protein synthesis.

codon: A codon is a sequence of three nucleotides in mRNA that corresponds to a specific amino acid or a stop signal during protein synthesis.

tRNA (transfer RNA): tRNA is a type of RNA that helps translate the genetic code from mRNA into an amino acid sequence by bringing the appropriate amino acids to the ribosome during protein synthesis.