A carbohydrate is an organic compound that is made up of carbon, hydrogen and oxygen and is considered as one of the major class of biomolecules.The general formula of carbohydrate is Cn(H2O)n. One of the most commonly known carbohydrate would be glucose which is one of the main energy source for living organisms.
Monosaccharides are the simplest carbohydrates such as glucose and galactose. They are generally aldehydes or ketones that have multiple hydroxyl groups attached. The smallest monosaccharides are dihydroxyacetone and D- and L-glyceraldehyde. Dihydroxyacetone is a ketose because it contains a keto group, whereas glyceraldehyde is an aldose because it contains an aldehyde group  (there are two stereoisomers of glyceraldehyde due to a single asymmetric carbon atom).
- ↑ Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman. pg 304