Learning Outcomes
By the end of this lesson, students should be able to:
i. Define carbohydrates and their classification based on the number of sugar units (monomers, dimers, oligomers, and polysaccharides).
ii. Identify the different types of monosaccharides (aldoses, ketoses, pentoses, and hexoses) based on their structure and functional groups.
iii. Explain the concept of glycosidic linkages and how they connect monosaccharides to form disaccharides and polysaccharides.
iv. Describe the structure and function of various polysaccharides, including starch, glycogen, cellulose, and chitin.
v. Appreciate the diverse roles carbohydrates play in biological systems, including energy storage, structural support, and cell recognition.
Introduction
Carbohydrates, a fundamental class of biomolecules, are ubiquitous in nature, serving as the primary energy source for organisms and playing crucial roles in various biological processes. They are composed of carbon, hydrogen, and oxygen atoms, typically in a ratio of (CH2O)n.
i. Classification of Carbohydrates
Carbohydrates are classified based on the number of sugar units they contain:
Monosaccharides: Simplest carbohydrates, containing a single sugar unit (e.g., glucose, fructose, galactose)
Disaccharides: Formed by the condensation of two monosaccharides through a glycosidic linkage (e.g., sucrose, lactose, maltose)
Oligosaccharides: Contain a small number of monosaccharides (typically 3-10) linked together (e.g., raffinose, stachyose)
Polysaccharides: Large, complex carbohydrates composed of numerous monosaccharides (e.g., starch, glycogen, cellulose, chitin)
ii. Types of Monosaccharides
Monosaccharides are further classified based on their structure and functional groups:
Aldoses: Monosaccharides with an aldehyde (-CHO) group (e.g., glucose, galactose)
Ketoses: Monosaccharides with a ketone (-CO-) group (e.g., fructose)
Pentoses: Monosaccharides with five carbon atoms (e.g., ribose, deoxyribose)
Hexoses: Monosaccharides with six carbon atoms (e.g., glucose, fructose, galactose)
iii. Glycosidic Linkages
Glycosidic linkages are the covalent bonds that connect monosaccharides to form disaccharides and polysaccharides. The type of glycosidic linkage determines the properties and functions of the carbohydrate.
iv. Structure and Function of Polysaccharides
Polysaccharides are diverse and structurally complex carbohydrates with various biological roles:
Starch: The primary storage polysaccharide in plants, providing energy for plant growth and development.
Glycogen: The storage polysaccharide in animals, found in the liver and muscles, serving as an energy reserve.
Cellulose: The structural polysaccharide in plant cell walls, providing rigidity and support.
Chitin: The structural polysaccharide in arthropod exoskeletons, providing protection and support.
Carbohydrates play a vital role in biological systems, serving as energy sources, structural components, and cell recognition molecules. Understanding the classification, structure, and function of carbohydrates provides a foundation for appreciating their diverse roles in living organisms.
