D-Ribose, β-D-Ribofuranose, D-2-Deoxyribose, β-D-2-Deoxyribofuranose

Many sugars exist in both open chain and cyclic forms. These forms are in equilibrium with each other, and interconvert. Ribose and deoxyribose behave in this way. The cyclic, or furanose, forms are those incorporated into nucleic acids. Once incorportated, there is no longer conversion to open chains – the 1'-hydroxy oxygen (the aldehyde oxygen in the open chain form) has been replaced by an N-glycosidic linkage to a nucleic acid base.