Significance of Nucleic Acids, Nucleotides, and Related Compounds in Infant Nutrition

Nucleotides are low molecular weight intracellular compounds that play major roles in physiological and biological functions. They act as precursors for nucleic acid synthesis and are also fundamental for intermediary metabolism. Nucleotides and nucleic acids turn over rapidly, especially in growing tissues or those undergoing constant cell renewal. Tissues that grow have a net formation of new DNA and a rapid turnover of RNA (1,2). Nucleotides are typically conformed by a nitrogenous base (purine or pyrimidine), a pentose (ribose or deoxyribose), and one or more phosphate groups. The nitrogenous bases are derived from two parent heterocyclic molecules. The major purines found in living organisms are adenine and guanine, while cytosine, thymidine, and uracil are the major pyrimidine bases. Nitrogenous bases can be formed de novo from amino acid precursors or reutilized after their release from nucleic acid breakdown via the salvage pathway. The purine ring carbon atoms formed by de novo synthesis are derived from the dispensable amino acids glycine, glutamine, and aspartate. The carbon atoms for the de novo synthesis of pyrimidines are derived from carbamoyl phosphate and aspartate. Figure 1 summarizes the structure and precursors needed for the biosynthesis of purine and pyrimidine bases. The energy cost of de novo synthesis of nitrogenous bases requires significantly more energy than the salvage process, 5 mol of ATP as opposed to 1 mol of ATP for each nucleotide monophosphate produced; thus from an evolutionary point of view the salvage pathway has a selective advantage for rapidly growing organisms (3,4).