Chapter 5: Carbohydrates

Introduction to Carbohydrates

Carbohydrates are essential biomolecules that play critical roles in cell structure, molecular identity, and energy storage. Their functions are determined by their chemical structure and how their monomers are linked together.

• Monosaccharides: Simple sugars, also called "one-sugar" monomers.

• Oligosaccharides: Short chains of monosaccharide units, "few-sugars" small polymers.

• Polysaccharides: Long chains of monosaccharide units, "many-sugars" large polymers.

Structure of Monosaccharides

Monosaccharides are the simplest carbohydrates and serve as building blocks for more complex carbohydrates. They have the general formula and must contain at least three carbon atoms, one carbonyl group, and two hydroxyl groups.

• General Formula: (e.g., glucose is )

• Functional Groups: Contains a carbonyl group (C=O) and multiple hydroxyl groups (-OH).

• Minimum Structure: At least 3 carbons, 1 carbonyl, and 2 hydroxyl groups.

Classification of Monosaccharides by Carbonyl Position

Monosaccharides are classified based on the position of their carbonyl group:

• Aldose: Carbonyl group at the end of the carbon chain.

• Ketose: Carbonyl group located internally within the carbon chain.

Example: Glucose is an aldose; fructose is a ketose.

Classification of Monosaccharides by Number of Carbons

Monosaccharides are also named according to the number of carbon atoms they contain:

• Triose: 3 carbons

• Tetrose: 4 carbons

• Pentose: 5 carbons

• Hexose: 6 carbons

Monosaccharides with the same number and type of atoms but different arrangements are called isomers.

Isomerism in Monosaccharides

Isomers are molecules with the same molecular formula but different structural arrangements. In monosaccharides, isomerism can occur due to:

• Different positions of the carbonyl group (aldose vs. ketose)

• Different arrangements of hydroxyl groups

Example: Dihydroxyacetone (a triose ketose) and glyceraldehyde (a triose aldose) are isomers.

Examples of Common Monosaccharides

• Glucose: A hexose aldose, primary energy source in cells.

• Fructose: A hexose ketose, found in fruits.

• Ribose: A pentose aldose, component of RNA.

Summary Table: Monosaccharide Classification

Key Points

• Carbohydrates are vital for cell structure, identity, and energy storage.

• Monosaccharides are classified by carbonyl position (aldose/ketose) and number of carbons (triose, tetrose, pentose, hexose).

• Isomerism leads to diversity in monosaccharide structure and function.

Additional info: These notes expand on the brief points in the slides to provide definitions, examples, and a summary table for clarity and completeness.