They are the simplest of the carbohydrates, the subunits from which disaccharides, oligosaccharides and polysaccharides are constructed. They are colourless, crystalline solids that are freely soluble in water but insoluble in nonpolar solvents and most of them have a sweet taste.

D-glucose (aldohexose)

D-fructose (ketohexose)

Monosaccharides have an unbranched carbon chain as a backbone, which all the carbon atoms are linked by single bonds. One of the carbon atoms is doble-bonded to an oxygen atom to form a carbonyl group (its position in the molecule define if it is an aldose or a ketose); each of the other carbon atoms has a hydroxyl group, which ones are often chiral centres.

The simplest monosaccharides are the two three-carbon trioses: glyceraldehyde, an aldose, and dihydroxycetone, a ketose. Monosaccharides with four, five, six and seven carbon atoms in their backbones are called, respectively, tetroses, pentoses, hexoses and heptoses.

Monosaccharides with five or more carbon atoms in the backbone usually occur in aqueous solution as cyclic (ring) structures, in which carbonyl group has formed a covalent bond with the oxygen of a hydroxyl group along the chain. This reaction results in an a or ß steroisomeric, a general reaction between aldehydes and alcohols to form derivates called hemiacetals. Such cyclic forms of sugars are called pyranoses, when they resemble the six-membered ring compound pyran, or furanoses, when they resemble the five-membered ring compound furan.

This biomolecule group can be oxidized by relatively mild oxidizing agents such as ferric (Fe3+) or cupric (Cu2+) ion. The carbonyl carbon is oxidized to a carboxylic acid. Glucose and other sugars capable of reducing ferric or cupric ion are called reducing sugars.

- Carbohydrates Metabolism;

-- Pentose Phosphate Pathway

-- Citric Acid Cycle

-- Glycolisys

-- Glycogen Breakdown

- Carbohydrates Biosynthesis

-- Glycogen Synthesis