Nucleic acids such as DNA and RNA are polymers of monomeric nucleotides. Each nucleotide is made up of phosphoric acid, sugar (5-carbon), and nitrogenous base (or nucleobase). There are five nitrogenous bases that serve as fundamental units of the genetic code: (1) adenine, (2) guanine, (3) cytosine, (4) thymine, and (5) uracil. These nitrogenous bases may be classified into purines and pyrimidines.
Adenine and guanine are purine (nitrogenous) bases. Adenine can be distinguished from guanine by its amine group at position 6 and the presence of an additional double bond between N-1 and C-6 in its heterocyclic aromatic (pyrimidine) ring. It has a chemical formula of C5H5N5.
Adenosine and deoxyadenosine are the nucleosides of adenine. The adenosine (i.e. an adenine bound to a ribose sugar) that is phosphorylated with three phosphoric acid groups becomes adenosine triphosphate (ATP). ATPs are energy-rich molecules that serve as an energy source for various metabolic activities (e.g. cellular respiration). Other forms of energy-rich molecules with adenine as constituent are the cofactors nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD). Apart from this, ATP also serves as one of the nucleotide monomeric units that build up the RNA molecule. The deoxyadenosine (i.e. an adenine bound to a deoxyribose sugar) that is phosphorylated with three phosphoric acid groups becomes deoxyadenosine triphosphate (dATP), one of the nucleotides that build up DNA molecule.
- Flavin adenine dinucleotide
- Nicotinamide adenine dinucleotide
- Nicotinamide adenine dinucleotide phosphate