Nucleotides and nucleic acids

A nucleotide is composed of a pentose sugar, a nitrogenous base, and one or more phosphate groups (Figure 1.4A). The pentose sugar can either be ribose (in a ribonucleotide ) or 2′-deoxyribose (in a deoxyribonuceotide ). The nitrogenous bases present in nucleic acids are the derivatives of purine (Adenine, A and Guanine, G) and pyrimidine (Thymine, T; Cytosine, C; and Uracil, U) (Figure 1.4B). Nucleotides, as you may know, are the structural units of nucleic acids. Apart from that, nucleotides such as adenosine triphosphate (ATP), guanosine triphosphate (GTP), coenzyme A (CoA), flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide (NAD⁺), and nicotinamide adenine dinucleotide phosphate (NADP⁺), play critical roles in metabolism and intracellular signaling.

Figure 1.4 Nucleotides and nucleic acids: structure of an ATP molecule, a nucleotide (A); structures of the sugars and different bases present in nucleic acids (B); double-helical structure of DNA (C); and structure of a tRNA molecule showing local secondary structures (D).