Metabolic pathway
Pyrimidines
Builds the ring first and attaches it to ribose afterwards, the other way round from purines. It ends in UMP, from which the other pyrimidine nucleotides come. One of its steps happens in the mitochondrial membrane and hands electrons to the respiratory chain.
- In
- Glutamine + 2 ATP + Aspartate + Ubiquinone + PRPP
- Out
- UMP + Glutamate + 2 ADP + 2 Inorganic phosphate + Ubiquinol + Pyrophosphate
- Location
- Cytosol
Fun facts
- Carbamoyl phosphate synthetase IIThe cell keeps the two pools of carbamoyl phosphate apart because it does not want nitrogen meant for disposal to be diverted into making DNA. The mitochondrial membrane is what enforces the separation.
- Aspartate transcarbamylaseIn bacteria this was the first enzyme in which allosteric regulation was described: its whole shape changes when its end product binds, and that finding opened the study of how a small molecule controls a large protein.
- Dihydroorotate dehydrogenaseThat is why making pyrimidines depends on respiration working. A cell without an active respiratory chain cannot make new DNA even if it has energy to spare from other sources.
- OMP decarboxylaseIt is one of the most efficient enzymes known: the reaction it catalyzes would take on the order of tens of millions of years to happen on its own.
Reactions
| # | Enzyme | ΔG°′ |
|---|---|---|
| 1 | Carbamoyl phosphate synthetase IIEC 6.3.5.5 · irreversibleGlutamine + Carbon dioxide + 2 ATP + Water → Carbamoyl phosphate + Glutamate + 2 ADP + Inorganic phosphate | — |
| 2 | Aspartate transcarbamylaseEC 2.1.3.2 · irreversibleCarbamoyl phosphate + Aspartate → Carbamoyl aspartate + Inorganic phosphate | — |
| 3 | DihydroorotaseEC 3.5.2.3Carbamoyl aspartate ⇌ Dihydroorotate + Water | — |
| 4 | Dihydroorotate dehydrogenaseEC 1.3.5.2 · irreversibleDihydroorotate + Ubiquinone → Orotate + Ubiquinol | — |
| 5 | Orotate phosphoribosyltransferaseEC 2.4.2.10 · irreversibleOrotate + PRPP → OMP + Pyrophosphate | — |
| 6 | OMP decarboxylaseEC 4.1.1.23 · irreversibleOMP → UMP + Carbon dioxide | — |
0 of 6 reactions with a documented ΔG.
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The data sheet includes the map. The logo goes at the bottom.
Sources
- Nelson, D. L. & Cox, M. M. (2021). Lehninger. Principios de bioquímica, 8.ª ed., ch. 22