Stop codon

Definition

A stop codon is a nucleotide triplet within mRNA that signals the termination of protein synthesis during translation. It plays a crucial role in ensuring that proteins are synthesized to their correct lengths by indicating to the ribosome when to stop adding amino acids to the growing polypeptide chain. There are three specific stop codons: UAA, UAG, and UGA, which do not correspond to any amino acid and instead trigger the release of the newly formed protein from the ribosome.

5 Must Know Facts For Your Next Test

1. Stop codons are essential for ensuring that proteins are synthesized correctly and do not extend beyond their intended length.
2. When a ribosome encounters a stop codon during translation, it recruits release factors that promote the disassembly of the ribosome and the release of the completed polypeptide.
3. The presence of multiple stop codons in the genetic code provides redundancy, allowing for some degree of error correction during protein synthesis.
4. Mutations that affect stop codons can lead to diseases or malfunctions in proteins, as they may result in truncated proteins or altered functions.
5. Stop codons are universally recognized in all organisms, highlighting their fundamental role in the biology of life.

Review Questions

• How do stop codons contribute to the regulation of protein synthesis during translation?
  • Stop codons serve as essential signals for terminating protein synthesis during translation. When the ribosome encounters a stop codon on the mRNA, it triggers a series of molecular events leading to the release of the completed polypeptide chain. This regulation ensures that proteins are synthesized accurately, preventing them from being longer than necessary, which could disrupt cellular functions.
• Discuss the implications of mutations in stop codons on protein functionality and cellular health.
  • Mutations in stop codons can have serious consequences for protein functionality and cellular health. If a stop codon is mutated to encode an amino acid instead, it can lead to a longer, non-functional polypeptide, potentially resulting in various diseases or disorders. Conversely, premature stop codons may cause truncated proteins that lack essential functional domains, leading to loss of activity and potentially harmful effects on cell function.
• Evaluate how understanding stop codons has impacted biotechnology and therapeutic approaches in modern medicine.
  • Understanding stop codons has greatly impacted biotechnology and therapeutic approaches in modern medicine by enabling researchers to design targeted therapies for genetic disorders caused by faulty protein synthesis. For example, gene therapy techniques can be developed to correct or bypass mutations affecting stop codons. Additionally, synthetic biology applications utilize knowledge of stop codons to engineer proteins with specific characteristics for drug development and other medical applications, showcasing their critical role in advancing healthcare solutions.

Related terms

Start codon: The first codon of a messenger RNA (mRNA) transcript that is recognized by the ribosome to initiate translation, commonly AUG, which codes for methionine.

Ribosome: A complex molecular machine found within all living cells that facilitates the translation of mRNA into proteins by catalyzing the assembly of amino acids.

Polypeptide:

A chain of amino acids linked by peptide bonds that fold into a specific three-dimensional structure to form a protein.