In the given structure, ring one (I) has one o-atom and is a 6 membered ring, thus is called pyranose ring, whereas ring (II) has one o-atom and is a five membered ring, thus is called furanose. The disaccharide is linked by a glycosidic bond between C −1 of glucose (in the α -position, α linkage) and C−2 of fructose (in the β -position, β -linkage).