<prompt> What is involved in formation of d-TMP from d-UMP: PGI June 2007N5, N10- methylene tetra hydrofolateForm imino folateN5 formyl folateDihydro folate  <response>: Ans: A N5, N10, Methylene tetrahydrofolate Lippincott 4th303-04: SaysdUMP is converted to dTMP by thymidylate synthase, which uses N5;N10-methylene tetrahydrofoiate Q as the source of the methyl group. This is u nasal reaction in that tetrahydrofoiate THF contributes not only a one carbon unit but also fwo hydrogen atoms from the pteridine ring, resulting in the oxidation of THF to dihydrofolate DHFJ.Inhibitors of thymidylate syn those includes thymine a nalogs such as 5-fluroruracilDHF can be reduced to THF by dihvdrofolate reductaseQ an enzyme that is inhibited in the presence of drugs such as methotrexateQ 