Learning Outcomes
i. Define polysaccharides.
ii. Classify polysaccharides into linear and branched polysaccharides.
iii. Describe the structure and function of different types of polysaccharides.
iv. Explain how polysaccharides are formed and broken down.
i. What are polysaccharides?
Polysaccharides are carbohydrates that are made up of many monosaccharides joined together by glycosidic bonds. Glycosidic bonds are covalent bonds that are formed between the carbon atom of one monosaccharide and the oxygen atom of another monosaccharide. Polysaccharides can be classified into two main groups: linear polysaccharides and branched polysaccharides.
ii. Linear polysaccharides
Linear polysaccharides have a straight chain of monosaccharides. Examples of linear polysaccharides include starch and cellulose.
Starch: Starch is a storage polysaccharide that is found in plants. Starch is made up of glucose molecules that are joined together by alpha glycosidic bonds. Starch is broken down into glucose by enzymes called amylases.
Cellulose: Cellulose is a structural polysaccharide that is found in plant cell walls. Cellulose is made up of glucose molecules that are joined together by beta glycosidic bonds. Cellulose is not broken down by enzymes in the human digestive system, but it can be broken down by bacteria in the gut.
iii. Branched polysaccharides
Branched polysaccharides have a branched chain of monosaccharides. Examples of branched polysaccharides include glycogen and chitin.
Glycogen: Glycogen is a storage polysaccharide that is found in animals. Glycogen is made up of glucose molecules that are joined together by alpha glycosidic bonds. Glycogen is broken down into glucose by enzymes called glycogen phosphorylases.
Chitin: Chitin is a structural polysaccharide that is found in the exoskeletons of arthropods, such as insects and crustaceans. Chitin is made up of N-acetylglucosamine molecules that are joined together by beta glycosidic bonds. Chitin is not broken down by enzymes in the human digestive system.
iv. Formation and breakdown of polysaccharides
Polysaccharides are formed when many monosaccharides are joined together by glycosidic bonds. This process is called dehydration synthesis. Dehydration synthesis is a condensation reaction, which means that a water molecule is removed when each glycosidic bond is formed.
The breakdown of polysaccharides into monosaccharides is called hydrolysis. Hydrolysis is the opposite of dehydration synthesis. Hydrolysis reactions require a water molecule to break each glycosidic bond.
Real-world applications of polysaccharides
Polysaccharides are used in a variety of products and industries. For example, starch is used in food products, such as bread, pasta, and cereal. Cellulose is used in paper, textiles, and other industrial products. Glycogen is used in the production of biofuels. Chitin is used in the production of cosmetics and dietary supplements.
Polysaccharides are important nutrients that provide energy, storage, and structural support for organisms. Polysaccharides are classified into linear and branched polysaccharides. Linear polysaccharides, such as starch and cellulose, have a straight chain of monosaccharides. Branched polysaccharides, such as glycogen and chitin, have a branched chain of monosaccharides. Polysaccharides are formed by dehydration synthesis and are broken down by hydrolysis.
