- When 2 monomer bond together covalently, they for DISACCHARIDES. This is formed via a condensation reaction and a “bridge” is created. This “bridge” is called a GLYCOSIDIC BOND. Some of these disaccharies are maltose, lactose and sucrose.
MALTOSE:
The glycosidic bond of maltose is formed between the OH of carbon 1 and carbon 4 of 2 glucose monomers. Thereforer, it forms an alpha (1–> 4) glycosidic bond.
NB: OH on both carbon 1 and carbon 4 anr below the plane (alpha), therefore, they are in close proximity.
LACTOSE:
This is a milk sugar, composed of a glucose and a galactose monomer. They form a beta (1–> 4) glycosidic bond.
NB: unlike Glucose, Lactose is a product of beta monomers. Therefore, the OH groups are above the plane on the anomeric carbon ie. carbon 1. The OH on the other monomer is always below the plane, therefore, the bond forms in a zig- zag manner because they are not both in close proximity.
SUCROSE:
Sucrose links the anomeric hydroxyls of glucose and fructose to form an alpha (1–>2) glycosidic bond.
- POLYSACCHARIDES are formed when chains of monosaccharide units link together. Some examples are starch, glycogen and cellulose.
STARCH:
Starch is made up of amylopectin and amylose.
Amylose is a straight chain with alpha (1–>4) linkages:
Amylopectin is an alpha (1–>4) chain with alpha (1–>6) branches. These branches occur after every 24 glucose residues.
GLYCOGEN:
Glycogen has a similar structure to amylopectin. The only difference is that glycogen is more branched, ie. every 10 glucosyl residues. Due to this high branched structure, glucose is released rapidly from glycogen stores.
CELLULOSE:
Cellulose is a straight chain polysaccharide with beta (1–>4) linkages. (Note the ig-zag shaped in the glycosidic bonds, symbolizing beta linkages. This allows cellulose to have high tensile strength.)
The Biochem Synapse 