C.3.3

=Carbohydrates - condensation of monosaccharides to form disaccharides and polysaccharides=

CONDENSATION/DEHYDRATION Reactions:
A reaction in which monosaccharides join together and release water as a product. An -H is removed from one molecule, and an -OH group from another, resulting in a glycosidic bond forming between the two monosaccharides to form disaccharides and eventually polysaccharides.

__**Sucrose**__ Formed from the condensation of α-glucose and β-fructose. The link between the two sugars is known as a glycoside link. In the case of sucrose, the link is between the C-1 atom of glucose in the α-configuration and the C-2 atom of fructose. The link is known as a β-1, 2 bond.
 * Disaccharides:**

The β-galactose is linked at the C-1 atom to the C-4 atom of β-glucose. The link is known as a β-1, 4 bond.
 * __Lactose__**



In lactose both galactose and glucose are the β isomer because the -OH groups are oriented in the following way in the plane: up, down, up, up.

**P**olysaccharides:
__**Starch**__ Exists in two forms: amylose and amylopectin.
 * Amylose** is water soluble, its structure is composed of a straight chain polymer of α-glucose units with α-1, 4 bonds. The molecules coil into a helical structure. It forms a colloidal suspension in hot water.
 * Amylopectin** is insoluble in water. Its structure also consists of α-D-glucose unites but has a branched structure with both α-1, 4 and α-1, 6 bonds. Most plants use starch as a store of carbohydrates and thus energy.