03 Pyrimidine

Synthesis

• create monophosphate version

• II: found in cytosol, rate limiting, inhibited by UMP

• I: in mito, for urea cycle

• bifunction: catalyzes 2 steps

• hypersegmented neutrophils

• letter U: orotic acid in Urine, Ump synthase, Uridine treatment

Thymidine

• adding methyl group to create thymidine

• folate to THF, add carbon to dUMP

• donate 1 carbon

• humans don't rely on PABA to make folate

• deficient in B12: all folate trapped in N5 methyl THF

• deficient in either folate or B12 leads to high homocysteine level

• MMA: fatty acid conversion