Termination

Definition

Termination refers to the final step in protein synthesis where the synthesis of a polypeptide chain is completed, resulting in the release of the newly formed protein. This process is crucial as it ensures that proteins are synthesized accurately and at the right time, maintaining cellular function and homeostasis. It involves specific signals that indicate the end of translation, ensuring that no extra amino acids are added to the growing chain.

5 Must Know Facts For Your Next Test

1. There are three specific stop codons in the genetic code: UAA, UAG, and UGA, which do not correspond to any amino acids.
2. Termination occurs when a release factor binds to the ribosome at a stop codon, prompting the release of the newly formed polypeptide from the tRNA.
3. After termination, the ribosomal subunits disassemble and can be reused for another round of translation.
4. In eukaryotes, termination involves additional factors such as eRF1 and eRF3, which work together to facilitate the process.
5. Errors during termination can lead to incomplete or malfunctioning proteins, which can have significant impacts on cellular functions and health.

Review Questions

• How does the presence of stop codons influence the process of termination in protein synthesis?
  • Stop codons play a critical role in termination as they signal to the ribosome that the polypeptide synthesis should end. When a stop codon is encountered during translation, no corresponding tRNA exists to bring an amino acid. Instead, a release factor binds to the ribosome at this site, facilitating the disassembly of the ribosomal complex and allowing for the release of the completed polypeptide chain. This mechanism ensures proteins are synthesized correctly and helps maintain cellular function.
• Discuss the roles of release factors in terminating protein synthesis and how they interact with ribosomes.
  • Release factors are essential proteins that recognize stop codons during translation termination. When a stop codon is present at the A-site of the ribosome, a release factor binds to it instead of a tRNA. This binding triggers conformational changes in the ribosome that promote hydrolysis of the bond between the polypeptide chain and its corresponding tRNA. This process allows for the release of the newly synthesized protein and ensures that translation comes to a proper conclusion.
• Evaluate how errors in termination can affect protein function and overall cellular health.
  • Errors in termination can lead to premature or incomplete protein synthesis, resulting in truncated polypeptides that lack essential functional domains. These malfunctioning proteins may misfold or aggregate, causing cellular stress and potentially triggering disease processes. For example, if a vital enzyme is improperly synthesized due to termination errors, it can disrupt metabolic pathways, leading to severe consequences for cellular function and overall health. Hence, accurate termination is crucial for maintaining proteostasis within cells.

Related terms

Stop Codon: A sequence of three nucleotides in mRNA that signals the termination of protein synthesis by signaling ribosomes to release the completed polypeptide chain.

Release Factor: A protein that recognizes the stop codon during translation termination and promotes the disassembly of the ribosome and the release of the newly synthesized protein.

Polypeptide Chain: A sequence of amino acids linked by peptide bonds, which folds into a functional protein after synthesis is complete.