Step 1: Understanding the Question:
5-Fluorouracil (5-FU) is an anti-metabolite used in cancer chemotherapy, and it needs to be converted into an active form inside the cell before it can act.
Step 2: Key Concept:
5-FU is a prodrug. Cells take it up and convert it, through the pyrimidine salvage pathway, into phosphorylated nucleotide forms. One of these, FdUMP, is the metabolite that actually does the damage.
Step 3: Detailed Explanation:
5-FU is converted stepwise to 5-fluoro-2-deoxyuridine and then phosphorylated to 5-fluoro-2-deoxyuridylic acid (FdUMP). This nucleotide forms a stable complex with the enzyme thymidylate synthase and its cofactor, blocking the conversion of dUMP to dTMP. Since dTMP is needed to make thymine for DNA, this block starves the cell of thymine and stops DNA synthesis, which is how 5-FU kills rapidly dividing cancer cells.
Step 4: Final Answer:
5-Fluorouracil is activated to 5-fluoro-2-deoxyuridylic acid (FdUMP).