Reality → Life → Biochem → Nucleic acids
Nucleic acids, a collective term for DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) [1] , are the pivotal macromolecules that carry the genetic code, transmit the information, and start the self-assembly of proteins. The molecules consist of long chains, made up of individual building blocks (nucleotides) joined together in linear arrangement through ester bonds [2] . Each nucleotide is composed of three compounds: a nucleobase [3] , a five-carbon sugar (ribose in RNA, deoxyribose in DNA), and a phosphate group. In the chromosomes of the cell nucleus, the sugar and phosphate units form the double helix backbone, while the nucleobases build the base pairs [4] that, by their sequence in the double helix, code for genetic information.
Nucleobases are nitrogenous organic bases consisting of carbon, nitrogen, hydrogen, and oxygen in a heterocyclic (C-N) structure. There are four different nucleobases that together with sugar and phosphate groups build the nucleotides of DNA and RNA. For DNA, the four bases are adenine, cytosine, guanine, and thymine; for RNA, the first three bases are the same, but the fourth base (thymine) is replaced by uracil.
The four nucleobases (A, C, G, T) build two base pairs: adenine (A) and thymine (T) form one base pair through two hydrogen bonds; and cytosine (C) and guanine (G) form the other base pair through three hydrogen bonds. The process relies on complementarity of donor and acceptor groups on the nucleobases' ring structures.