Figure 10.2 Common monosaccharides. Aldoses contain an aldehyde (shown in blue), whereas ketoses, such as fructose, contain an ketose (shown in blue). The asymmetric carbon atom farthest from the aldehyde or ketone (shown in red) designates the structures as being in the configuration. The numbers are the standard designations for the positions of the carbon atoms (e.g., the number 2 identifies the carbon atom in the second position).