Final answer:
Antimetabolites are drugs that inhibit enzymes crucial for synthesizing nucleotide bases, which are necessary for DNA and RNA synthesis, affecting cancer cells and infectious agents by hindering their replication.
Step-by-step explanation:
Antimetabolites are drugs that interfere with one or more enzymes or their reactions that synthesize nucleotide bases or nucleosides needed for DNA and RNA synthesis. They are typically used in the treatment of cancer and some infectious diseases. For example methotrexate affects the enzyme responsible for converting folic acid to tetrahydrofolic acid, which is a coenzyme necessary for synthesis of purines and pyrimidines.
5-Fluorouracil (5-FU) is another antimetabolite that inhibits the synthesis of thymidine nucleotide, resulting in diminished DNA production. Antimetabolites like sulfonamides and trimethoprim disrupt bacterial synthesis of folic acid critical for nucleotide biosynthesis, by serving as competitive inhibitors. Drugs such as sulfadiazine, pyrimethamine and spiramycin target parasitic infections by inhibiting key enzymes in their metabolic pathways.