Stop codon

Definition

A stop codon is a specific sequence of three nucleotides in mRNA that signals the termination of protein synthesis during translation. These codons do not code for any amino acids and play a crucial role in ending the polypeptide chain, allowing ribosomes to release the newly formed protein. Understanding stop codons is essential as they ensure that proteins are synthesized correctly and that the genetic information is accurately translated into functional molecules.

5 Must Know Facts For Your Next Test

1. There are three main stop codons: UAA, UAG, and UGA, which are recognized by release factors during translation.
2. Stop codons do not have corresponding tRNA molecules, meaning they signal the end of polypeptide synthesis rather than adding an amino acid.
3. When a stop codon is reached, the ribosome releases the completed polypeptide chain into the cytoplasm or into the endoplasmic reticulum for further processing.
4. The presence of stop codons prevents the translation machinery from continuing indefinitely, ensuring that proteins are synthesized according to the instructions in the mRNA.
5. Mutations in stop codons can lead to diseases or dysfunctional proteins, as premature or extended translation can disrupt normal cellular functions.

Review Questions

• How do stop codons contribute to the process of protein synthesis, and what would happen if they were absent?
  • Stop codons play a vital role in terminating protein synthesis by signaling the ribosome to release the newly formed polypeptide chain. If stop codons were absent, the ribosome would continue to translate mRNA indefinitely, potentially resulting in excessively long and non-functional proteins. This could disrupt normal cellular functions and lead to detrimental effects on an organism's health.
• Discuss how mutations affecting stop codons can influence protein function and contribute to disease.
  • Mutations that create premature stop codons can lead to truncated proteins that lack essential functional domains, resulting in loss of activity. Conversely, mutations that change or eliminate stop codons can cause extended translation, producing proteins that are abnormally long and may misfold or interact incorrectly with other cellular components. Both scenarios can lead to various diseases, highlighting the importance of precise codon usage in maintaining cellular health.
• Evaluate the significance of stop codons in genetic regulation and their potential implications for genetic engineering.
  • Stop codons are crucial for regulating gene expression and protein production within cells. In genetic engineering, precise manipulation of stop codons can allow scientists to control protein synthesis more accurately. By inserting or modifying stop codons in engineered genes, researchers can create proteins with specific lengths or functionalities, which has applications in developing therapeutics or studying protein functions. This understanding opens new avenues for innovation in biotechnology and medicine.

Related terms

Start codon: A start codon is the first codon of a messenger RNA (mRNA) transcript that is translated by a ribosome, usually AUG, which also codes for the amino acid methionine.

Ribosome: A ribosome is a molecular machine composed of ribosomal RNA and proteins that synthesizes proteins by translating messenger RNA (mRNA) into polypeptide chains.

tRNA (transfer RNA): tRNA is a type of RNA that transports specific amino acids to the ribosome during protein synthesis, matching its anticodon with the corresponding codon on the mRNA.