AS and A Level Biology 12 Views 1 Answers
Avatar for Sourav Pan
Sourav PanOctober 28, 2024

Describe the formation of a glycosidic bond by condensation, with reference to disaccharides, including sucrose, and polysaccharides

Describe the formation of a glycosidic bond by condensation, with reference to disaccharides, including sucrose, and polysaccharides

Sourav Pan
Sourav PanOctober 28, 2024

Answered step-by-step

A glycosidic bond forms when two monosaccharides join together through a condensation reaction (also called dehydration synthesis), where a molecule of water is released. This bond can form between various hydroxyl groups of the participating monosaccharides, creating either an α-glycosidic or a β-glycosidic bond, depending on the orientation of the linkage.

Formation of a Glycosidic Bond in Disaccharides

  1. Example with Sucrose:
    • In the formation of sucrose (a non-reducing disaccharide), an α-glucose molecule and a β-fructose molecule join together.
    • The glycosidic bond forms between the hydroxyl group on the C1 of glucose (α-1) and the C2 of fructose (β-2), resulting in an α(1→2) glycosidic bond.
    • As a result of this linkage, both the anomeric carbons are involved in the bond, making sucrose a non-reducing sugar with no free aldehyde or ketone groups.
  2. Example with Maltose:
    • In maltose (a reducing disaccharide), two α-glucose molecules join together.
    • The glycosidic bond forms between the C1 of one glucose and the C4 of the second glucose, creating an α(1→4) glycosidic bond.
    • Unlike sucrose, maltose retains a free anomeric carbon (C1 of the second glucose unit), allowing it to act as a reducing sugar.

Formation of Glycosidic Bonds in Polysaccharides

  • Polysaccharides are formed by linking multiple monosaccharides through repeated glycosidic bonds. The specific types of glycosidic linkages and the sequence of monosaccharides determine the structure and function of the polysaccharide.
  • For instance, starch (in plants) and glycogen (in animals) are storage polysaccharides composed of α-glucose units connected primarily by α(1→4) glycosidic bonds, with branching points formed by α(1→6) glycosidic bonds.
  • Cellulose, a structural polysaccharide in plant cell walls, consists of β-glucose molecules linked by β(1→4) glycosidic bonds. This arrangement allows cellulose chains to form strong, rigid fibers due to hydrogen bonding between adjacent chains.

Start Asking Questions

This site uses Akismet to reduce spam. Learn how your comment data is processed.

⚠️
  1. Click on your ad blocker icon in your browser's toolbar
  2. Select "Pause" or "Disable" for this website
  3. Refresh the page if it doesn't automatically reload