What forms after the glycosidic linkage reaction between glucose and galactose is complete?
A. Water and lactose
B. Mannose
C. Lactose
D. Water and fructose
The correct answer and explanation is :
The correct answer is: A. Water and lactose
Explanation:
When glucose and galactose, two monosaccharides, undergo a glycosidic linkage reaction, they form the disaccharide lactose. This is a condensation (or dehydration synthesis) reaction, meaning it involves the removal of a water molecule during the process of bond formation.
Here’s what happens in more detail:
- Monosaccharide Structure:
Both glucose and galactose are hexose sugars (six-carbon sugars) and are structural isomers, meaning they have the same molecular formula (C₆H₁₂O₆) but different structures. - Formation of Glycosidic Linkage:
The hydroxyl (-OH) group on carbon 1 (C1) of galactose reacts with the hydroxyl group on carbon 4 (C4) of glucose, forming a β-1,4-glycosidic bond. This is why lactose is specifically known as β-D-galactopyranosyl-(1→4)-D-glucose. - Water is Released:
In the process, one molecule of water (H₂O) is removed—one hydrogen (H) from the hydroxyl of galactose and a hydroxyl group (OH) from glucose. This loss of water is characteristic of condensation reactions. - Product:
The result is lactose, a disaccharide made up of glucose and galactose, and water as a byproduct.
Why other options are incorrect:
- B. Mannose: This is another monosaccharide, not involved in this reaction.
- C. Lactose: Only partially correct; it omits water, a key byproduct.
- D. Water and fructose: Fructose is not part of this reaction; it’s involved in forming sucrose (glucose + fructose).
Final Summary:
When glucose and galactose join via a glycosidic linkage, the products are lactose and water. This is a typical dehydration synthesis reaction forming a disaccharide.