Thymidylate formation from thymidine

Cells that are synthesizing DNA mnst also be able to synthesize deoxy thymidine triphosphate (dTTP). The key step in the synthesis is the conversion of dUMP to dTMP via thymidylate synthetase. The reaction reqnires a sonrce of N, -methylene tetrahydrofolate to provide the methyl gronp. In this reaction the tetrahydrofolate is oxidized to dihydrofolate. Dihydrofolate is rednced to tetrahydrofolate via dihydrofolate reductase so more methylene If, A °-tetrahydrofolate is made from serine in a reaction that is catalyzed by serine hydroxymethyltransferase. These three reactions, which are essential for the formation of dTMP, are shown in Fig. 14-20. 

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