Monosaccharides: The Building Blocks of Carbohydrates
Monosaccharides are the simplest form of carbohydrates, containing 3 to 8 carbon atoms. They are classified based on their carbon content and functional groups.
Definition: Monosaccharides are simple sugars that cannot be broken down into simpler sugars through hydrolysis.
Types of Monosaccharides:
- Trioses (C3): Examples include glyceraldehyde and dihydroxyacetone
- Pentoses (C5): Such as ribose and deoxyribose
- Hexoses (C6): Most common, including glucose and fructose
Vocabulary: Aldehyde group (-CHO) and ketone group (C=O) are key functional groups in monosaccharides.
Chemical Properties of Monosaccharides:
- Highly soluble in water
- Sweet taste
- Chemically neutral
- Exist in both chain and ring forms
Example: Glucose can exist in an open-chain form or a cyclic form, with the cyclic form being more stable in aqueous solutions.
Oligosaccharides: Intermediate Carbohydrates
Oligosaccharides consist of 2 to 10 monosaccharide units linked by glycosidic bonds. The most common are disaccharides.
Highlight: The most biologically significant disaccharides are sucrose (table sugar), lactose (milk sugar), and maltose (product of starch digestion).
Examples of Important Disaccharides:
- Sucrose: Glucose + Fructose
- Lactose: Glucose + Galactose
- Maltose: Glucose + Glucose
Vocabulary: Glycosidic bond - A covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate.
Polysaccharides: Complex Carbohydrates
Polysaccharides are large molecules composed of many monosaccharide units linked by glycosidic bonds. They can have straight or branched chains and are typically insoluble in water.
Example: Starch is a plant polysaccharide used for energy storage, while cellulose provides structural support in plant cell walls.
Key Polysaccharides:
- Starch (in plants)
- Cellulose (in plant cell walls)
- Glycogen (in animals and fungi)
- Chitin (in fungi and arthropod exoskeletons)
