Ribose and deoxyribose (in RNA and DNA respectively) are pentose sugars. DNA contains a deoxygenated form of ribose called deoxyribose. DNA and RNA are built up of the monosaccharides deoxyribose and ribose, respectively. Nucleosides are molecules formed by attaching a nucleobase to a ribose or deoxyribose ring. For example, dATP stands for deoxyribose adenine triphosphate. Thymine combined with deoxyribose creates the nucleoside deoxythymidine, which is synonymous with the term thymidine. Nucleotides in DNA contain a deoxyribose sugar, a phosphate, and a nucleobase. If cytosine is attached to a deoxyribose ring, it is known as a deoxycytidine. A deoxyribonucleoside is a type of nucleoside including deoxyribose as a component. In 1929, Levene identified deoxyribose sugar in "thymus nucleic acid" (DNA). This order of reactivity parallels the exposure to solvent of the deoxyribose hydrogens. The related deoxyribose is a component of DNA. Levene went on to discover deoxyribose in 1929. Deoxyribose has the formula and ribose the formula . Deoxyribose was discovered in 1929 by Phoebus Levene.