Page 103 - General Biochemistry

PYRIMIDINE RIBONUCLEOTIDE SYNTHESIS

Pyrimidine ribonucleotide synthesis

• Pyrimidine ribonucleotides are uracil and cytosine, during their synthesis
uridine Monophosphate (UMP) is synthesized first, then CTP is synthesized
from UMP

• Pyrimidine ring synthesis completed first; then attached to ribose-5-
phosphate

• Nucleoside monophosphate kinase catalyzes transfer of Pi to UMP to form
UDP; nucleoside diphosphate kinase catalyzes transfer of Pi from ATP to
UDP to form UTP

• CTP formed from UTP by CTP Synthetase driven by ATP hydrolysis
Orotic Aciduria

It is a disease that is due to a defect of an enzyme that is involved in pyrimidine
synthesis thus leading to over production of orotic acid in urine because of the
inability to convert orotic acid to UMP

Symptoms: retarded growth; severe anemia
It is considered the only known inherited defect in this pathway as all others

would be lethal to fetus
Treatment: with uridine/cytidine
Q: HOW DOES URIDINE AND CYTIDINE ADMINISTRATION WORK TO
TREAT OROTIC ACIDURIA?

A: The administration of uridine monophosphate (UMP) or uridine triacetate
(which is converted to UMP). These medications will bypass the missing
enzyme and provide the body with a source of pyrimidines

102