Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologyeasymcq1 pt

A drug inhibits topoisomerase ahead of a replication fork but does not directly inhibit helicase or DNA polymerase. What is the most likely immediate effect?

A.RNA primers can no longer be synthesized
B.The leading strand switches to 3′→5′ synthesis
C.DNA ahead of the fork becomes increasingly overwound
D.Sister chromatids separate before replication finishes

Explanation

Core Concept

Opening the DNA helix creates torsional strain ahead of the replication fork. Topoisomerase relieves that strain by transiently breaking and rejoining DNA. If topoisomerase is inhibited, positive supercoiling accumulates ahead of the fork and replication slows or stalls.

Correct Answer

CDNA ahead of the fork becomes increasingly overwound

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