MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A patient is diagnosed with a genetic disorder caused by a mutation that leads to the premature termination of protein synthesis. This mutation results in a shortened, non-functional protein. Analysis of the mRNA sequence reveals that a normal codon for an amino acid has been replaced by a stop codon. What type of mutation is this?
- ASilent mutation
- BFrameshift mutation
- CNonsense mutation
- DMissense mutation
Show answer & explanationAnswer & explanation
Correct answer: C. Nonsense mutation
A nonsense mutation occurs when a point mutation changes a codon that normally codes for an amino acid into a premature stop codon, leading to the production of a truncated, often non-functional protein.
Why the other options are wrong
- A. A silent mutation changes a nucleotide but does not change the amino acid sequence.
- B. A frameshift mutation involves the insertion or deletion of nucleotides not in multiples of three, altering the reading frame.
- D. A missense mutation results in a codon that codes for a different amino acid.
Nonsense Mutation
A type of point mutation where a single nucleotide change results in a premature stop codon, leading to a truncated protein.
- Changes an amino acid codon to a stop codon.
- Results in a shorter, non-functional protein.
- A form of point mutation.
- Can have severe phenotypic consequences.
Memory trick: Nonsense: No More Sense, Just Stop