Glucose can be linked together to form cellulose and starch through a process called polymerization, specifically through glycosidic bonding. Both cellulose and starch are polysaccharides made up of long chains of glucose molecules, but they differ in their structure and function.
Starch:
- Structure: Starch is primarily composed of two types of molecules: amylose and amylopectin. Amylose is a linear polymer of glucose units linked through α(1→4) glycosidic bonds, while amylopectin is a branched polymer that contains both α(1→4) linkages and α(1→6) linkages at the branch points.
- Function: Starch serves as an energy storage molecule in plants. When plants require energy, enzymes break down starch into glucose.
Cellulose:
- Structure: Cellulose consists of long chains of glucose units linked by β(1→4) glycosidic bonds. This type of bonding causes the glucose chains to have a straight, linear structure, which allows for the formation of strong hydrogen bonds between adjacent chains, resulting in a rigid and stable fiber.
- Function: Cellulose is a key structural component in the cell walls of plants, providing strength and rigidity.
Summary of Glycosidic Bonds:
- α(1→4) Glycosidic Bond: Used in starch (both amylose and amylopectin) - creates a curved structure that is suited for storage.
- β(1→4) Glycosidic Bond: Used in cellulose - creates a straight structure that can form strong fibers.
Formation of Glycosidic Bonds:
The glycosidic bond formation occurs through a dehydration (or condensation) reaction where a hydroxyl (-OH) group from one glucose molecule reacts with the hydroxyl group of another glucose molecule, releasing a molecule of water (H₂O).
In summary, while both cellulose and starch are made of glucose units, their different types of glycosidic bonds and resulting structures lead to different functions in biological systems.