Click on image to view larger version.
Fig. 1. Principal Components of the Folate Biochemical Cycle. Abbreviations: DHFR = dihydrofolate reductase; MTHFR = methylenetetrahydrofolate reductase. Reactions: 
Biosynthesis of nucleotides for incorporation into DNA and RNA; 
Remethylation of homocysteine to form methionine (vitamin B12 serves as a coenzyme in this reaction); 
Methylation of substrates, including DNA, RNA, phospholipids, and proteins; 
MTHFR, which catalyzes the formation of 5-methyltetrahydrofolate needed for methylation reactions; 
Dihydrofolate reductase enzyme.
