Mannose is a monosaccharides. Containing six carbons and an aldehyde group, it is classified as an aldose and a hexose. Mannose is a constituent of glycoproteins and a few polysaccharides. Mannose is phosphorylated by hexokinase to mannose-6-phosphate, which is readily isomerized to fructose-6-phosphate for entry into glycolysis or gluconeogenesis (Figure 13.12).