Simple sugars or monosaccharides

The two main types of sugars are monosaccharides and disaccharides. Monosaccharides consist of a single sugar molecule.

Monosaccharides may contain from three to nine carbon atoms although most of them contain five or six. A three carbon monosaccharide is called a triose; one containing four carbons is called a tetrose; five, a pentose; six, a hexose; seven, a heptose; eight an octose and nine a nonose.

*Pentoses (Arabinose, ribose, xylose)
The pentose sugars, deoxyribose and ribose, are essential components of the genetic material DNA and RNA. E.g. glucose and fructose: (C6H12O6); arabinose and xylose: (C5H10O5).

Arabinose is found in gums and when several arabinose molecules are joined together, a pentosan formed.

*Hexoses
-Aldohexoses – galactose, glucose
-Ketohexose - fructose
All hexoses have the same chemical formula C6H12O6, but slightly different structures. In nature, only fructose and glucose occur in free form. Galactose joined with glucose forms the disaccharide lactose.

Glucose is a hexose. Octoses and nanoses are quite rare. Glucose, the main source of energy for body cells, is found in most sweet fruits and in blood.
Simple sugars or monosaccharides