DNA Replication & Repair MCAT Practice Question
During DNA replication in mammalian cells, a mutation in the gene encoding DNA polymerase delta (Pol δ) results in loss of 3' to 5' exonuclease activity while maintaining intact polymerase catalytic activity. Researchers observe a dramatic increase in mutation rate throughout the genome after several rounds of replication. What is the most likely explanation for this elevated mutation rate?
Answer choices
- DLoss of exonuclease activity eliminates the proofreading mechanism that normally detects and removes mismatched nucleotides immediately after incorporationCorrect answer
- ADNA polymerase delta cannot extend primers synthesized by primase, blocking lagging strand synthesis
- BThe mutation prevents binding of replication factor C (RFC) to the sliding clamp, destabilizing the replication fork
- CDNA polymerase delta cannot process Okazaki fragments, causing accumulation of single-strand breaks in lagging strand DNA
- EExonuclease activity is required for nucleotide excision repair, so its loss impairs removal of UV-induced thymine dimers
- FThe 3' to 5' exonuclease activity is essential for removing the RNA primers left by primase, and its loss prevents completion of Okazaki fragment maturation
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