Overview
This lecture covers the structure, classification, and functions of carbohydrates, focusing on the differences between monosaccharides, disaccharides, and polysaccharides.
Carbohydrate Basics
- Carbohydrates are biomolecules made of carbon, hydrogen, and oxygen in a 1:2:1 ratio (CH₂O).
- "Saccharide" means sugar; classified by the number of sugar units as mono-, di-, or polysaccharides.
Monosaccharides
- Monosaccharides are single sugar units and are the building blocks (monomers) of all carbohydrates.
- Common monosaccharides: glucose (main energy source), fructose (in fruits/plants), and galactose (in milk).
- All listed monosaccharides have the formula C₆H₁₂O₆ and can be in straight-chain or ring forms.
Disaccharides
- Disaccharides consist of two monosaccharides joined by dehydration reactions forming glycosidic linkages.
- Examples include maltose (glucose + glucose), sucrose (glucose + fructose), and lactose (glucose + galactose).
Polysaccharides
- Polysaccharides are long chains of glucose units, serving as energy storage or structural molecules.
- Starch (amylose—straight chains, amylopectin—branched) is the plant energy storage polysaccharide.
- Glycogen, highly branched, is the animal energy storage polysaccharide.
- Cellulose (straight chain, unbreakable by most organisms) strengthens plant cell walls.
- Chitin (with amino groups) is structural in animals and fungi, like insect exoskeletons.
- Peptidoglycan (with peptide chains) is found in bacterial cell walls, making them flexible and rugged.
Simple vs. Complex Carbohydrates
- Simple sugars: monosaccharides and disaccharides.
- Complex carbohydrates: polysaccharides.
Key Terms & Definitions
- Monosaccharide — single sugar molecule; building block of carbohydrates.
- Disaccharide — two monosaccharides linked together.
- Polysaccharide — many monosaccharides linked, forming long chains.
- Glycosidic linkage — bond formed between sugar units by dehydration.
- Dehydration reaction — chemical process that joins molecules by removing water.
Action Items / Next Steps
- Review the formulas and structures of common monosaccharides, disaccharides, and polysaccharides.
- Prepare for questions differentiating simple and complex carbohydrates.