A 4-Year-Old Boy Is Brought to the Physician for Fatigue

A 4-year-old boy is brought to the physician for fatigue and persistent bone pain.  Physical examination shows diffuse lymphadenopathy and multiple purpura over his arms and legs.  Laboratory analysis reveals anemia and thrombocytopenia, and a peripheral blood smear shows lymphoblasts.  After further workup, he is diagnosed with acute lymphoblastic leukemia and started on a chemotherapy regimen that includes doxorubicin.  This agent intercalates between DNA base pairs and inhibits DNA replication, a process that normally occurs at sites known as replication forks.  As the replication forks move across the DNA molecule, 2 distinct daughter strands are formed.  Which of the following is unique to the daughter strand that is synthesized in the opposite direction of the growing replication fork?

A) Synthesis of multiple, short DNA fragments
B) 5'→3' exonuclease activity of DNA polymerase
C) 3'→5' exonuclease activity of DNA polymerase
D) 3'→5' polymerase activity of DNA polymerase
E) RNA primer synthesis before DNA strand synthesis

Correct Answer:

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