April 2010
Written by Sigrid Auweter

Chemically, sugars are a combination of carbon (C) and water (H2O) and are therefore also called carbohydrates. Glucose, for example, is a 6-carbon sugar and can be written as C6H12O6.

There are, however, many different sugars that share the same chemical formula. Mannose, for instance, is another 6 carbon-sugar and hence has the same chemical formula as glucose. Glucose and mannose differ in the relative positioning of hydrogen atoms and hydroxyl (OH) groups along the 6-carbon chain.

Sugars such as glucose form ring structures, where one ring member is an oxygen atom, while the remaining ring is made up of carbon.

 Chemical structure of glucose. (click to enlarge the image)


Sugars can form bonds with one another. Regular household sugar, for example, is a two-unit sugar consisting of one unit of fructose and one unit of glucose. Starch, a molecule used for energy storage in plants, is made of long chains of glucose units.

The bond between sugars connects to hydroxyl (OH) groups. As all sugars have a large number of hydroxyl groups, there are many of different ways the sugar units can be linked. This property allows for branched carbohydrates. Glycogen, a molecule that animals use as an energy store, consists of highly branched glucose units.

 A branched carbohydrate containing glucose units. (click to englarge image)