American Board of Surgery Qualifying Exam (ABS QE) Practice Test 2026 - Free Surgery Exam Practice Questions and Study Guide

5-Fluorouracil (5-FU) is a chemotherapeutic agent that primarily functions by inhibiting thymidylate synthase, an enzyme critical for DNA synthesis. Thymidylate synthase catalyzes the conversion of deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP), which is essential for DNA replication and repair. By inhibiting this enzyme, 5-FU effectively disrupts the synthesis of thymidine, leading to a decrease in DNA production and ultimately resulting in cell cycle arrest and apoptosis in rapidly dividing cancer cells.

The other enzymes mentioned are not inhibited by 5-FU. Dihydrofolate reductase is targeted by drugs like methotrexate, while DNA polymerase is involved in DNA replication and is not directly affected by 5-FU. RNA polymerase, responsible for synthesizing RNA, does not play a direct role in the mechanism of action of 5-FU, which is primarily focused on DNA synthesis interruption.