Structure and Classification of Carbohydrates - SS3 Chemistry Lesson Note

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen atoms. They serve as essential sources of energy and structural components in living organisms. Carbohydrates are classified based on their chemical structure and the number of sugar units they contain. Let's explore the structure and classification of carbohydrates in detail:

Structure of Carbohydrates:

1.    Monosaccharides: Monosaccharides are the simplest carbohydrates, consisting of a single sugar unit. They have the general formula (CH2O)n, where "n" is usually 3, 4, 5, 6, or 7 carbon atoms. Common monosaccharides include glucose (C6H12O6), fructose (C6H12O6), and galactose (C6H12O6).

2.    Disaccharides: Disaccharides are formed by the condensation of two monosaccharides with the elimination of a water molecule. Each disaccharide has its specific combination of monosaccharides. Common disaccharides include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).

3.    Oligosaccharides: Oligosaccharides are carbohydrates composed of 3 to 10 monosaccharide units linked together. They are often found as components of glycoproteins and glycolipids, playing roles in cell recognition and signalling.

4.    Polysaccharides: Polysaccharides are large carbohydrates consisting of many monosaccharide units linked together. They serve as energy storage molecules (e.g., starch in plants, glycogen in animals) and structural components (e.g., cellulose in plant cell walls, chitin in the exoskeleton of insects).

Classification of Carbohydrates:

1.    Aldoses and Ketoses: Monosaccharides can be further classified into aldoses and ketoses based on the presence of an aldehyde (aldose) or a ketone (ketose) functional group. Aldoses have an aldehyde group at the end of the carbon chain, while ketoses have a ketone group in the middle of the carbon chain.

2.    Trioses, Tetroses, Pentoses, Hexoses, etc.: Monosaccharides are classified based on the number of carbon atoms they contain. For example, trioses have three carbon atoms, tetroses have four, pentoses have five, and hexoses have six. The number of carbon atoms in a monosaccharide determines its overall structure and properties.

3.    Reducing and Non-Reducing Sugars: Some carbohydrates can act as reducing agents due to the presence of a free aldehyde or ketone group. Monosaccharides and most disaccharides are reducing sugars, while some disaccharides (e.g., sucrose) are non-reducing sugars.

The different structures and classifications of carbohydrates contribute to their diverse functions in living organisms. Monosaccharides are the building blocks of more complex carbohydrates, and polysaccharides serve as energy reserves and structural elements. Carbohydrates play crucial roles in various biological processes, making them essential for life and an important area of study in biochemistry and nutrition.