Deoxyribonucleic acid (DNA) is a biomolecule that carries genetic information (i.e. the genes). It occurs in all living organisms and in some types of viruses. The word is composed of the prefix des-, oxygenium (oxygen), ribose and nucleic acid. In the normal state, the DNA has the shape of a double helix. Chemically, these are nucleic acids – long chain molecules (polymers), which are constructed of four different building blocks. Each of these blocks referred to as nucleotides consists of a phosphate residue, the sugar deoxyribose and an organic base (adenine, thymine, guanine or cytosine, abbreviated A, T, G and C).

Genes store the information required for the production of ribonucleic acids (RNA). An important group of RNA, the mRNA, contains the information needed to build the proteins necessary for the biological development and cellular metabolism of a living organism. The base sequence within the protein-coding genes determines the sequence of the amino acids of the respective protein. Three such bases encode a particular amino acid.

In eukaryotes, which include plants, animals and fungi, most of the DNA is organized in the form of chromosomes in the cell nuclei; a small part can be found in the mitochondria. In plants and algae, DNA is also found in the chloroplasts (the organelles in which photosynthesis takes place). In bacteria and archaea, which belong to the non-nucleated prokaryotes, the DNA is located in the cytoplasm. RNA viruses, on the other hand, do not store the genetic information in the DNA but in the RNA.