Nonsense mutation

Definition

A nonsense mutation is a type of DNA mutation where a change in the nucleotide sequence creates a premature stop codon, leading to the early termination of protein synthesis. This can severely affect the function of the resulting protein, as it often results in a truncated protein that may be nonfunctional or harmful. Nonsense mutations can arise from various factors, such as errors during DNA replication or exposure to certain chemicals.

5 Must Know Facts For Your Next Test

1. Nonsense mutations can lead to serious genetic disorders, as the proteins produced are often incomplete and cannot perform their normal functions.
2. These mutations are usually caused by point mutations, where a single nucleotide is substituted, which changes an amino acid codon into a stop codon.
3. In some cases, nonsense mutations can be partially suppressed by downstream mechanisms like read-through, where ribosomes ignore the stop codon and continue translation.
4. The severity of the impact from a nonsense mutation depends on the position of the premature stop codon; earlier stop codons typically result in more severe protein truncation.
5. Some therapeutic strategies aim to counteract the effects of nonsense mutations by using compounds that promote read-through of premature stop codons.

Review Questions

• How do nonsense mutations affect protein synthesis and function?
  • Nonsense mutations cause premature termination of protein synthesis by introducing a stop codon into the mRNA sequence. This results in truncated proteins that are usually nonfunctional or have altered functions, which can lead to severe physiological consequences. For example, if a critical protein involved in cellular processes is truncated due to a nonsense mutation, it may not be able to perform its necessary roles, potentially leading to diseases or dysfunctions.
• Compare and contrast nonsense mutations with other types of mutations such as missense and frameshift mutations regarding their impact on protein structure.
  • Nonsense mutations create early stop codons that truncate proteins, often resulting in nonfunctional polypeptides. In contrast, missense mutations change one amino acid in the protein sequence but may still allow for functional proteins depending on how critical that amino acid is to the protein's structure. Frameshift mutations alter the entire downstream reading frame, potentially leading to extensive changes in the protein structure. While all three types can impact protein function, their effects vary greatly based on how they modify the protein's amino acid sequence.
• Evaluate the potential therapeutic approaches for addressing diseases caused by nonsense mutations and their implications for genetic medicine.
  • Therapeutic approaches for managing diseases caused by nonsense mutations often focus on promoting read-through of premature stop codons using pharmacological agents. This method allows ribosomes to continue translating the mRNA past the stop signal, potentially producing full-length proteins. Additionally, gene therapy techniques aim to correct or replace defective genes harboring nonsense mutations. These strategies illustrate the growing field of genetic medicine aimed at providing targeted treatments for genetic disorders caused by specific mutations, thereby improving patient outcomes and advancing personalized medicine.

Related terms

Missense Mutation: A missense mutation is a type of mutation that results in a single amino acid change in a protein, which can alter its function but does not necessarily lead to a complete loss of activity.

Frameshift Mutation: A frameshift mutation occurs when nucleotides are added or deleted from the DNA sequence, causing a shift in the reading frame and often resulting in completely altered protein sequences.

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.