Principles of Biochemistry Volume 2 - A. Lehninger 1985

Bioenergetics and Metabolism
The ATP Cycle and Cellular Bioenergetics
In addition to ATP, there are other high-energy nucleotide 5'-triphosphates

Uridine triphosphate (UTP), guanosine triphosphate (GTP), and cytidine triphosphate (CTP) are phosphorylated ribonucleotides structurally similar to ATP (Fig. 14-18) and characterized by the same Standard Free energy of Hydrolysis, ∆G⁰'. These compounds are present in all Cells, albeit in significantly smaller amounts than ATP. Corresponding deoxyribonucleoside-5'-triphosphates—2'-deoxyadenosine-5'-triphosphate (dATP), 2'-deoxyguanosine-5'-triphosphate (dGTP), 2'-deoxycytidine-5'-triphosphate (dCTP), and 2'-deoxythymidine-5'-triphosphate (dTTP)—are also found in cells in low concentrations. While ATP serves as the primary carrier of phosphate groups in The Cell, the other nucleoside-5'-triphosphates listed here perform specialized Functions, driving strictly defined biosynthetic pathways. They receive their terminal phosphate groups from ATP in Reactions Catalyzed by Mg²⁺-dependent Enzymes known as nucleoside diphosphokinases. These enzymes catalyze the following reversible reactions:

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Fig. 14-19. Various nucleotide and deoxynucleoside triphosphates serve as the conduits through which ATP energy is directed toward The Biosynthesis of specific cellular components.

Figure 14-19 illustrates how these various nucleoside and deoxynucleoside triphosphates channel energy and building blocks into specific metabolic pathways, where they are utilized for the biosynthesis of Lipids, Proteins, and most importantly, DNA and RNA.