Disaccharides are formed when two monosaccharides join together. The bond that holds them together is called a glycosidic bond. This bond is formed by a condensation reaction, in which a water molecule is released. The type of glycosidic bond determines the properties and functions of the disaccharide.
Definition
Glycoside: A glycoside is basically a ring chain hexose (6C) or pentose (5C) sugar molecule that is attached usually to another sugar molecule.
Glycosidic Bond: Covalent chemical bonds between two glycosides that hold them together is called a glycosidic bond.
In simple words: A glycosidic bond is the link between two sugar molecules.
Core Concept
Glycosidic bonds are formed due to condensation reactions between two sugar molecules (mostly hexoses).
For the formation of a glycosidic bond:
The H-group from one ringed sugar interacts with the -OH group of another sugar.
One water molecule is released.
Glycosidic linkages are present in:
Disaccharides
Oligosaccharides
Polysaccharides
Detailed Explanation
Formation of Glycosidic Bond
Steps:
Two monosaccharides come close together.
The H-group from one ringed sugar interacts with the -OH group of another sugar.
A water molecule is released.
A glycosidic bond is formed between the two sugars.
General Equation:
Sugar 1 + Sugar 2 → Disaccharide + Water
Naming of Glycosidic Bonds
Glycosidic bonds are named on the basis of:
Carbon number of interacting carbons of both linked sugars.
Alpha or beta type of the first sugar involved in the linkage.
α-1,4-glycosidic linkage is formed when:
The first sugar is alpha.
It donates the -OH group from its C-1.
The other sugar donates the H-group from its fourth carbon.
Format: α-1,4 or α-1, α-4
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