Final answer:
Polysaccharides are formed when two disaccharides undergo a dehydration reaction to create a new glycosidic bond. The repeated addition of disaccharides through this process can form long-chain polysaccharides used for energy storage or structural support.
Step-by-step explanation:
Polysaccharides can be made from two disaccharides through a process similar to that which forms disaccharides from monosaccharides. When two disaccharides undergo a dehydration reaction (also known as condensation reaction or dehydration synthesis), they can be linked together. This involves the removal of a water molecule and the formation of a new covalent bond known as a glycosidic bond or glycosidic linkage.
Each disaccharide is composed of two monosaccharide units joined by a glycosidic linkage. Therefore, to form a polysaccharide, the anomeric carbon of one disaccharide's monosaccharide unit reacts with a hydroxyl group of another monosaccharide unit in a second disaccharide, thereby releasing a water molecule and extending the chain. This step can be repeated multiple times with additional disaccharides to create a long-chain polysaccharide.
Common disaccharides such as sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose) are examples of this process. Once linked to form polysaccharides, they can be stored for energy or provide structural support in various organisms. In an acidic aqueous solution, these chains can be hydrolyzed back into monosaccharides.