Transcription & Translation MCAT Practice Question
A 34-year-old woman with a history of recurrent infections and progressive neurological decline presents with cognitive impairment and ataxia. Genetic testing reveals a novel mutation in the NEMF gene, which encodes a component of the ribosome-associated quality control (RQC) complex. Laboratory studies show accumulation of truncated polypeptides and polyubiquitinated protein aggregates in her fibroblasts. When her cells are exposed to amino acid starvation, ribosomal stalling occurs at rare codons, but the defective RQC machinery fails to resolve these stalled ribosomes efficiently. Which of the following best explains the pathophysiological consequence of this NEMF mutation?
Answer choices
- AInability to proteolytically degrade stalled ribosomes and nascent polypeptides, leading to accumulation of toxic truncated proteins and depletion of free ribosomal subunitsCorrect answer
- BImpaired aminoacyl-tRNA synthetase recognition of rare codons, resulting in decreased translation fidelity at non-standard positions
- CFailure of nonsense-mediated decay (NMD) pathway activation, allowing read-through translation of premature stop codons
- DReduced recruitment of elongation factors to the stalled ribosome, preventing ribosomal frameshifting and codon repositioning
- EDecreased expression of tRNA genes encoding rare amino acids, limiting the aminoacyl-tRNA pool available for translation
- FImpaired mRNA export from the nucleus, causing accumulation of incompletely translated transcripts in the nucleolus
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