03 Pyrimidine

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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