DNA Replication & Repair MCAT Practice Question
A 35-year-old woman with a family history of early-onset breast cancer undergoes genetic testing and is found to carry a heterozygous BRCA1 mutation. A colleague explains that cells with BRCA1 mutations accumulate more mutations over time compared to cells with defects in non-homologous end joining (NHEJ) proteins, despite both pathways repairing double-strand breaks (DSBs). Which of the following best explains why BRCA1 deficiency is particularly problematic for genomic stability?
Answer choices
- BHomologous recombination mediated by BRCA1 accurately restores the original DNA sequence using the sister chromatid as a template, whereas NHEJ is error-prone and often introduces indels at break sitesCorrect answer
- ABRCA1 is the only DSB repair protein expressed during S phase, whereas NHEJ proteins are constitutively expressed throughout the cell cycle
- CBRCA1 mutations prevent all spontaneous DNA damage, whereas NHEJ deficiency only impairs repair of radiation-induced breaks
- EBRCA1 repairs all types of DNA lesions, while NHEJ only repairs a minor fraction of total genomic damage
- DNHEJ protein defects cause cell death, whereas BRCA1 mutations allow cells to survive but with accumulating mutations
- FBRCA1-mediated homologous recombination is the backup pathway for NHEJ, so BRCA1 deficiency leaves cells without any functional repair mechanism
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