DHFR (Dihydrofolate Reductase) is an enzyme that plays a key role in DNA synthesis and repair. It catalyzes the conversion of dihydrofolate to tetrahydrofolate, a necessary cofactor for producing purines, thymidylate, and certain amino acids. This process is essential for cell growth and division, making DHFR a critical target in cancer treatment, where inhibitors like methotrexate block its activity to halt rapidly dividing cells.