MCAT® ExamBiological and Biochemical Foundations of Living SystemsEasy
A patient is diagnosed with a genetic disorder caused by a mutation that leads to the production of a truncated protein. Subsequent analysis reveals that the mutation resulted in a premature stop codon within the mRNA sequence. This type of mutation is best described as a:
- AMissense mutation
- BFrameshift mutation
- CNonsense mutation
- DSilent mutation
Show answer & explanationAnswer & explanation
Correct answer: C. Nonsense mutation
A nonsense mutation is a point mutation that results in a premature stop codon, leading to the termination of protein synthesis and the production of a truncated (shortened) protein.
Why the other options are wrong
- A. A missense mutation results in a change in a single amino acid, not a premature stop codon.
- B. A frameshift mutation results from insertions or deletions not divisible by three, altering the reading frame and typically leading to a completely different protein sequence and often a premature stop codon, but 'premature stop codon' is the direct and specific outcome described.
- D. A silent mutation changes a nucleotide but does not change the amino acid sequence due to codon degeneracy.
Nonsense Mutation
A point mutation in a DNA sequence that results in a premature stop codon during mRNA transcription, leading to the synthesis of a truncated, and often non-functional, protein.
- Changes an amino acid codon to a stop codon.
- Causes premature termination of translation.
- Results in a truncated protein.
- Often leads to loss of protein function.
Memory trick: Nonsense! Stop the protein!