Stop Codon

Definition

A stop codon, also known as a termination codon, is a sequence of three nucleotides in messenger RNA (mRNA) that signals the end of the coding sequence for a protein. These codons instruct the ribosome to release the completed polypeptide chain and dissociate from the mRNA, terminating protein synthesis.

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 do not specify an amino acid, but rather signal the termination of protein synthesis.
3. The recognition of a stop codon by the ribosome triggers the release of the completed polypeptide chain and the dissociation of the ribosome from the mRNA.
4. Proper recognition and interpretation of stop codons is crucial for ensuring the accurate synthesis of proteins with the correct amino acid sequence.
5. Mutations in stop codons can lead to premature termination of protein synthesis, resulting in the production of truncated or nonfunctional proteins.

Review Questions

• Explain the role of stop codons in the process of protein synthesis.
  • Stop codons play a critical role in protein synthesis by signaling the end of the coding sequence and instructing the ribosome to release the completed polypeptide chain. When the ribosome encounters a stop codon, it recognizes this as the termination signal, triggering the dissociation of the ribosome from the mRNA and the release of the newly synthesized protein. This ensures that the protein is produced with the correct amino acid sequence and length, which is essential for its proper folding and function.
• Describe the different types of stop codons and their significance in the genetic code.
  • The three stop codons in the genetic code are UAA, UAG, and UGA. These three codons do not specify any amino acids, but rather signal the end of the protein-coding sequence. The recognition of these stop codons by the ribosome is a crucial step in the termination of protein synthesis. The presence of multiple stop codons in the genetic code provides redundancy and ensures that the ribosome can reliably identify the end of the coding region, reducing the risk of premature termination or the production of incomplete proteins.
• Analyze the potential consequences of mutations in stop codons and their impact on protein synthesis.
  • Mutations in stop codons can have significant consequences for protein synthesis and the resulting protein structure and function. A mutation that changes a stop codon to a sense codon (one that specifies an amino acid) can lead to the continued translation of the mRNA beyond the intended termination point, resulting in the production of a longer, potentially nonfunctional protein. Conversely, a mutation that creates a new stop codon within the coding sequence can result in the premature termination of protein synthesis, leading to the production of a truncated and likely non-functional protein. These types of mutations can have profound effects on the cellular processes that depend on the proper function of the affected protein, highlighting the critical importance of accurate stop codon recognition and interpretation during protein synthesis.

Related terms

Genetic Code: The set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins by living cells.

Ribosome: A complex molecular machine found within all living cells that is responsible for the synthesis of proteins.

Polypeptide Chain: A long, unbranched polymer of amino acids linked together by peptide bonds, which is the precursor to a functional protein.