Monosaccharides are simple carbohydrates with multiple alcohol groups with or without ketone or aldehyde groups. The number of carbon atoms varies:
- 3 - trioses
- 5 - pentoses
- 6 - hexoses
Each monosaccharide may exist in stereoisomeric forms according to the sequence of side groups around a particular carbon atom. A given stereoisomer may be the unique substrate for a given enzyme.
They are all members of the sugar group.