Methotrexate complex diagram illustrating the effects and mechanisms of action of methotrexate Key Points and Connections (Based on the Image): Dihydrofolate Reductase (DHFR) Inhibition: Methotrexate competitively inhibits DHFR, a crucial enzyme in the folate pathway. This leads to decreased synthesis of tetrahydrofolate (THF), a cofactor essential for DNA and RNA synthesis. DNA and RNA Synthesis Inhibition: Reduced THF availability impairs the synthesis of purines and thymidylate, essential building blocks of DNA and RNA. This slows down cell proliferation, particularly in rapidly dividing cells like cancer cells. Cell Cycle Arrest: Methotrexate can arrest the cell cycle at the S phase, preventing DNA synthesis and cell division. Immune System Modulation: Methotrexate can suppress the immune system by inhibiting T-cell proliferation and cytokine production. This can be beneficial in autoimmune diseases but can also increase the risk of infection. Side Effects: The diagram highlights various side effects, including bone marrow suppression, gastrointestinal issues, and liver toxicity. These side effects are due to the non-specific nature of methotrexate's action on rapidly dividing cells. Additional Notes: The diagram is quite detailed and complex, making it difficult to extract all the information in a linear text format. The handwritten text and the complexity of the diagram may introduce some ambiguity in interpretation. It's important to consult with a healthcare professional or a medical expert for accurate and up-to-date information about methotrexate and its effects.