By Jason Chang and Brianna Chang
These are the simplest of carbohydrates and are known as simple sugars. They are the building blocks for bigger carbohydrates such as polysaccharides. Monosaccharides usually have the same formula of (CH2O)n , with “n� being 3, 5, or 6. Example: Glucose Glucose is the most important carbohydrate fuel in human cells. Its small size allows it to move through the cell membrane and then into the cell. Energy is released when the molecules are metabolised (C6H12O6 + 6O2 --> 6CO2 + 6H2O). This is part of the process of respiration.
Most of the sugars found in nature are actually disaccharides since monosaccharides are fairly rare. Monosaccharides form a glycosidic bond between each other as a result of a condensation reaction. This process requires energy and releases water. Example: Sucrose Sucrose is formed from an alpha-glucose and an alphafructose. It is the most common sugar product used for consumption. It is also a non-reducing sugar, which means that it is not easily oxidized by a weak oxidizing agent.
Monosaccharides go through a series of condensation reactions, adding one unit after another to the chain until very large molecules (polysaccharides) are formed. This is called condensation polymerisation. The properties of a polysaccharide molecule depend on: its length (though they are usually very long), the extent of any branching (addition of units to the side of the chain rather than one of its ends), any folding which results in a more compact molecule, and whether the chain is 'straight' or 'coiled'. Example: Starch Starch is made by plants to store energy. It exists in two forms which are Amylopectin and Amylose. Both are made from alpha- glucose. Amylopectin is insoluble and Amylose forms a colloidal suspension in hot water.
Oligosaccharides are formed from only a few number of monosaccharides. They have additional functional groups, which give them special properties. They are often covalently bonded to proteins and lipids on the outer surface, where they serve as recognition signals. Example: Fructo-oligosaccharides (FOS) Fructo-oligosaccharides are considered prebiotics. Prebiotics are non-digestible nutrients that selectively promote the growth of normal intestinal bacteria that may have beneficial effects on the large intestinal lining.