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Synthesis of Pyrimidine Ribonucleotides

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Description

Synthesis of the Pyrimidines is less complex than that of the Purines, since the base is much simpler. Synthesis of Carbamoyl-P (Carbamoyl Phosphate) is the first reaction of Pyrimidine biosynthesis. Carbamoyl-P is formed from HCO3- (Bicarbonate) and the amide nitrogen of Glutamine by the cytosolic enzyme CPSase (Carbamoyl Phosphate Synthetase). This reaction consumes two molecules of ATP (Adenosine Monophosphate): One provides a phosphate group and the other energizes the reaction. Then condensation of Carbamoyl-P with Asp (Aspartate or L-Aspartate or Aspartic Acid) occurs to form CAA (N-Carbamoyl-L-Aspartate) which is catalyzed by ATCase (Aspartate Carbamoyltransferase). This reaction is the flux-generating step and occurs without need of ATP because Carbamoyl-P is intrinsically activated. The reaction forming Pyrimidine ring yields Dihydroorotate ((S)-4,5-Dihydroorotate) in [...]

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