dxtxpx
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A female was delievered at39 weeks of normal pregnancy. She had severe megaloblastic anemia which was not ameliorated by vit B12 or folic acid. Her urine contained crystals of orotic acid. the dx of orotic acidemia/aciduria was made
1)Oral adminstration of which compound would lessen orotate excretion?
a) uridine
b) adenine
c) guanine
d) carbamoyl phosphate
e) PRPP
2) Which of the following enzymes is the pt most likely lacking?
a) hypoxanthine guanine phosphoribosyl transferase
b) duhydroorotase
c) carbamoyl phosphate synthetase II
d) orotodylic pyrophosphrylase-orotodylic decarboxylase
e) phosphoribosyl pyrophosphate synthetase
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| peekay
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i thind -D and C respectively
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| dxtxpx
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no try again
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| asmi
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1.E
2.A
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| dxtxpx
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Correct answers are 1)a 2)d
Orotic acidemia is a rare disorder presumably occuring with equal frequency in both males and females due to the fact that it is caused by an AR mutation altering the activity of orotodylic pyrophosphorylase-orotodylic decarboxylase, a key enzyme in pyrimidine synthesis pathway. These two distinct enzymatic activites are found in single gene product with a MW=51,000. Administration of uridine or cytidine bypasses the blockage and supplies nucleotides for RNA and DNA synthesis in rapidly growing hematopoietic tissues. In addition, these nucleotides lead to increaed production of UTP, a feedback inhibtor of carbamoyl phosphate snthetase II, which in turn leads to decreased orotic acid production
De novo synthesis of pyrimidines occurs via a six step set of reactions. The C2 and N3 of pyrimidine ring are formed when glutamine and CO2 form carbamoyl phosphate. ATP is consumed inthis reaction which is catalyzed by carbamoyl phosphate synthetase (CPS) II, an enzyme of cytosol, distinct from mitochondrial CPS I. The N1 and C4-6 of pyrimidine ring are added when carbamoylaspartate, due to action of aspartate carbamoyltransferase. The pyrimidine ring is then closed by dihydroorotase to form dihydroorotate which is then oxidized by dihyroorotate dehydrogenase, an NAD+ requiring flavoprotein. The N-riboside bond is formed next when orotate phosphoribosyltransferase catalyzes the combination of orotate with PRPP to form orotidine 5-monophosphate (OMP). OMP-decarboxylase completes the formation of UMP. The synthesis of cytidine nucleotides occurs at triphosphate level. The enzyme CTP synthetase converts UTP to CTP and requires glutamine and ATP.
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| asmi
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thanks for the explanation...actually we should have read the question properly.
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