DNA Replication & Repair MCAT Practice Question
A patient with Lynch syndrome (hereditary nonpolyposis colorectal cancer) has a germline mutation in MLH1, a mismatch repair (MMR) gene. Tumor cells isolated from this patient show microsatellite instability (MSI) with expansion of short tandem repeats throughout the genome. Which mechanism best explains how loss of mismatch repair function leads to microsatellite instability?
Answer choices
- BLoss of MLH1 impairs telomerase activity, leading to progressive shortening of microsatellite repeat regions
- DMLH1 deficiency prevents recognition and repair of base-pairing mismatches in microsatellite regions, allowing replication errors to accumulateCorrect answer
- AMLH1 normally recruits topoisomerase II to stabilize the replication fork during synthesis of repetitive sequences
- CMLH1 activates nucleotide excision repair pathways specific to repetitive DNA sequences in the genome
- EMLH1 normally prevents slippage of DNA polymerase on repetitive templates by increasing polymerase processivity
- FMLH1 deficiency impairs homologous recombination repair of double-strand breaks occurring within microsatellite regions during DNA replication
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