Question

Methotrexate is a drug that is commonly used to treat cancers and autoimmune diseases in humans. It functions by binding to the active site of the enzyme dhfr, preventing both DNA synthesis and excess cell proliferation. Which of the following terms best describes methotrexate?

1) cofactor
2) allosteric activator
3) noncompetitive inhibitor
4) competitive inhibitor

Answer 1

Methotrexate acts as a competitive inhibitor by binding to the active site of DHFR, an enzyme necessary for DNA synthesis, thereby inhibiting cell proliferation in conditions like cancer and autoimmune diseases.

Step-by-step explanation:

Methotrexate functions by inhibiting the enzyme dihydrofolate reductase (DHFR), which is crucial for the synthesis of tetrahydrofolic acid, an essential component for DNA synthesis. This inhibition is a result of methotrexate's structural similarity to folic acid, allowing it to bind tightly to the active site of DHFR, preventing the enzyme from catalyzing the conversion of folic acid to tetrahydrofolic acid. Given this mechanism of action, methotrexate is best described as a competitive inhibitor.

Drugs that function as competitive inhibitors block the enzyme's active site, prohibiting the substrate from binding and thus preventing the enzyme's normal function. This is a common strategy used in various therapeutic agents to control diseases such as cancer, gout, and some infections by targeting specific metabolic pathways.