Ribonucleic acids (RNA) are organic acids that play a decisive role in the formation of new proteins in cells (protein biosynthesis). They are located in the cell nucleus and cytoplasm of the cells in the form of single-stranded, thread-like macromolecules. Human RNA is composed of four organic bases: Adenine, guanine, cytosine and uracil, which are linked together by a sugar and phosphate backbone. The combination of one sugar, one phosphate residue and one of the four bases is called nucleotide. The nucleotides are the basic building blocks of RNA and DNA.

There are different types of RNA that perform different functions. For example, mRNA (messenger RNA) enables the transmission of information from the cell nucleus to the ribosomes, which are used to synthesize proteins. tRNA (transfer RNA) serves as an auxiliary molecule in the provision of individual amino acids for protein biosynthesis from the cytoplasm to the ribosome, and the ribosomes themselves are also two-thirds ribonucleic acid, rRNA (ribosomal RNA). Certain ribonucleic acids can also have gene-regulating functions or transfer genetic information.

Like RNA, deoxyribonucleic acid (DNA) is a nucleic acid that stores the genetic information of a cell and thus represents the material that the genes are made of. The structure of RNA and DNA is similar. The DNA molecule also consists of a sugar and phosphate backbone and four different bases. Three of these - adenine, guanine and cytosine - are identical to those in RNA. Instead of uracil, however, the fourth base is thymine. The sugar that links the bases together with the phosphate is also slightly different. Unlike RNA, it is not ribose, but deoxyribose, hence the different names of the two acids. 

In contrast to single-stranded RNA, DNA is double-stranded. The structure of DNA, discovered in 1953 by the scientists James Watson and Francis Crick, resembles a double helix. This can be imagined as a spiral-shaped twisted rope ladder, with the longitudinal connections always consisting alternately of a sugar and a phosphoric acid and the transverse connections each consisting of two of the four bases, which are connected to each other by transient hydrogen bridge connections. The sequence of three bases or nucleotides represents the genetic code (codon) for an amino acid.