The nitrogenous base is bonded to carbon-1 and the phosphate at carbon-5. The sugar in DNA is deoxyribose, which has only a hydrogen atom but no oxygen at carbon-2. The pentose sugar in RNA is ribose, which has a hydroxyl group attached to carbon-2. Their chemical structures differ depending on which pentose sugar and nitrogenous bases they contain. There are two types of nucleic acids: deoxyribonucleic acid, DNA, and ribonucleic acid, RNA. Nucleic acids are polymers of nucleotides – molecules composed of a pentose sugar, a nitrogen-containing base, and a phosphate group.