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Phosphate anhydrides and esters are a very important class in biochemistry. They include such compounds as ATP, Glucose 6-Phosphate, Glyceraldehyde 3-phosphate, Dihydroxyacetone phosphate, and proteins that have been activated by phosphorylation of serine, threonine or tyrosine residues. An anhydride is a compound that can be derived from another compound by subtracting a molecule of water. Pyrophosphate is the name for the structure formed when one phosphate is attached to another through dehydration. In other words, pyrophospate anion is the acid anhydride of phosphate. Many biochemical reactions, including the synthesis of UDP glucose, a form of glucose activated for the biosynthesis of glycogen, and the formation of Acyl CoA in fatty acid metabolism, are driven the eventual hydrolysis of pyrophosphate.
The phosphate group of a phosphate anhydride is a good leaving group for acyl substitution. Carbamoyl phosphate is another important phosphate anhydride in biochemistry. Carbamoyl phosphate is a precursor to urea and to pyrimidines. The committed step in pyrimidine biosynthesis occurs when the amine group of aspartate serves as the nucleophile to displace the phosphate from carbamoyl phosphate.