Stop codon

Definition

A stop codon is a specific nucleotide sequence in messenger RNA (mRNA) that signals the termination of protein synthesis during translation. These codons play a crucial role in ensuring that the newly synthesized polypeptide chain is released from the ribosome when the entire coding sequence has been read, marking the end of elongation and leading to the final steps of translation termination.

5 Must Know Facts For Your Next Test

1. There are three stop codons in the genetic code: UAA, UAG, and UGA, which do not code for any amino acids.
2. When a ribosome encounters a stop codon, it does not add an amino acid but instead recruits release factors that facilitate the disassembly of the ribosome-mRNA complex.
3. Stop codons are critical for ensuring that proteins are synthesized correctly and that any unnecessary translation is avoided, preventing the production of non-functional or harmful proteins.
4. Mutations that introduce or alter stop codons can lead to diseases by causing premature termination of protein synthesis or by extending proteins beyond their functional limits.
5. The recognition of stop codons by the ribosome is part of the larger process of translation termination, which also includes the hydrolysis of the bond between the completed polypeptide and the tRNA in the P site.

Review Questions

• How do stop codons function in the process of translation termination?
  • Stop codons function by signaling the ribosome to halt protein synthesis. When a ribosome encounters one of the three stop codons (UAA, UAG, UGA) during translation, it does not bind any tRNA carrying an amino acid. Instead, release factors are recruited, which promote the release of the newly synthesized polypeptide chain from the ribosome, effectively concluding the translation process.
• Discuss the consequences of mutations that affect stop codons in mRNA.
  • Mutations that introduce or change stop codons can have serious implications for protein synthesis. A premature stop codon may lead to truncated proteins that lack essential functional domains, potentially resulting in loss-of-function disorders or diseases. Conversely, if a mutation results in a missing stop codon, it can lead to elongated proteins that may misfold and become toxic. Both scenarios highlight the importance of accurate stop codon signaling in maintaining cellular health.
• Evaluate the importance of stop codons in maintaining genetic integrity and preventing disease.
  • Stop codons are vital for maintaining genetic integrity as they ensure proteins are synthesized to their correct lengths and functional forms. Proper termination prevents aberrant protein products that can disrupt cellular processes or lead to disease states. When translation goes awry due to mutations affecting stop codons, it can trigger various diseases, emphasizing their role as essential checkpoints in gene expression and protein synthesis regulation. Understanding their function also aids in developing targeted therapies for genetic disorders related to translation errors.

Related terms

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.

ribosome:

A ribosome is a complex molecular machine found within all living cells that synthesizes proteins by translating messenger RNA (mRNA) into polypeptide chains.

amino acid: An amino acid is a building block of proteins, linked together by peptide bonds to form polypeptide chains during the process of translation.