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DNA repair Transitional Reasoning Practice

Biology · Molecular Genetics · Biology · DNA Structure & Replication

1 Biology practice questions on DNA repair. Questions that build towards applied reasoning.

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Questions

  1. 1.

    A molecular genetics researcher investigates a bacterial strain that exhibits a significantly elevated rate of spontaneous mutations following DNA replication. Biochemical analysis reveals that while mismatch recognition and excision proteins remain fully active, the strain carries a loss-of-function mutation in the DNA methyltransferase gene responsible for tagging adenine bases at specific recognition sequences. Based on this repair mechanism, what is the primary consequence leading to the elevated mutation rate in this strain?

    • A) DNA polymerase III is unable to proofread newly added nucleotides because the 3'-to-5' exonuclease active site requires methylated adenine residues.
    • B) Ultraviolet-induced pyrimidine dimers can no longer be recognized or excised by the nucleotide excision repair endonuclease complex.
    • C) The mismatch repair machinery cannot distinguish the newly synthesized strand from the parental template strand, resulting in indiscriminate excision and mutation fixation.
    • D) DNA ligase fails to form phosphodiester bonds during Okazaki fragment maturation because it requires adenine methylation as an activation signal.

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