Carbohydrates: Structure, Types, and Functions

Carbohydrates

Overview and Chemical Structure

Carbohydrates (saccharides) are organic molecules composed mainly of carbon, hydrogen, and oxygen, typically with the empirical formula $C_n(H_2O)_n$. They serve as a primary source of short-term energy for most organisms and play structural roles in cells.

• Monosaccharides are the simplest carbohydrate monomers and are water-soluble, white, crystalline solids.

• Carbohydrates are classified based on the number of monomeric units: monosaccharides, disaccharides, and polysaccharides.

• Monosaccharides can repetitively link to form polysaccharides (complex carbohydrates).

Example: Monosaccharide monomers can polymerize to form polysaccharide polymers.

Monosaccharides

Monosaccharides are simple sugars with several hydroxyl groups (-OH) and are therefore polyhydroxy compounds. The most abundant monosaccharide is glucose ($C_6H_{12}O_6$), which can be used by most organisms as fuel or to build structures.

• Monosaccharides are named with the suffix -ose (e.g., glucose, fructose, sucrose, lactose, hexose, pentose).

• Monosaccharide units are linked by glycosidic bonds to form disaccharides and polysaccharides.

Example: Glucose monomers are linked via glycosidic bonds to form polysaccharides.

Polysaccharides

Polysaccharides are large carbohydrate polymers formed by linking many monosaccharide units. They serve various functions depending on their structure and composition.

• Starch, glycogen, cellulose, and pectin are examples of polysaccharides with varying functions.

• Polysaccharides can be covalently linked to proteins (glycoproteins), lipids (glycolipids), and nucleic acids (nucleotides).

Example: Starch is used for energy storage in plants, glycogen for energy storage in animals, and cellulose for plant cell wall structure.

Table: Polysaccharides and Their Functions

Polysaccharide	Function
Starch	Energy Storage in plants
Glycogen	Energy Storage in animals
Cellulose	Plants Cell Walls

Key Terms and Concepts

• Monosaccharide: The simplest form of carbohydrate; single sugar unit.

• Polysaccharide: A carbohydrate composed of many monosaccharide units linked together.

• Glycosidic bond: The covalent bond that joins carbohydrate (sugar) molecules to another group.

• Hydroxyl group: Functional group (-OH) present in all monosaccharides.

Practice Questions (with Answers)

• Which of the following expresses the correct chemical formula of a carbohydrate? Answer: $C_6H_{12}O_6$

• Which of the following matches the function of the polysaccharide glycogen? Answer: Energy storage in animals

Additional info:

• Carbohydrates are also involved in cell recognition and signaling (e.g., glycoproteins and glycolipids).

• DNA nucleotides contain a carbohydrate component (deoxyribose sugar).