RNA is a polynucleotide: it is made up of nucleotide units. Each nucleotide consists of a phosphoric acid, a ribose and an organic nucleobase containing nitrogen, which is typically cytosine, uracil, adenine and guanine, except in a few cases. RNA typically does not have a double helix structure.
The single RNA chain may bend backwards, and each chain section may form base pairs with hydrogen bonds, thus forming a double structure on certain parts of the chain.
The best known types of RNA are mRNA, tRNA and rRNA, which play an important role in protein synthesis within cells. Other RNA molecules regulate the expression of genes while certain RNA molecules act as enzymes, or biological catalysts. These are called ribozymes.
RNA is used in research, biotechnology, and molecular medicine.