Overview
This lecture covers the molecular basis of life, focusing on water's unique properties, acids and bases, and an introduction to carbohydrates and sugars.
Water and Its Properties
- Complete metabolism of carbohydrates yields carbon dioxide and water.
- Water acts as a solvent for many biological reactions due to its polarity.
- Water is a polar molecule with partial negative (oxygen) and positive (hydrogen) charges.
- Hydrogen bonding in water leads to properties like surface tension.
- Surface tension allows light objects to rest on water and causes phenomena like suction cup adhesion.
- Surfactant in lungs reduces surface tension, aiding newborns in breathing.
- Detergents and soaps disrupt hydrogen bonds, reducing surface tension and forming bubbles.
Acids, Bases, and pH
- Acids donate hydrogen ions (H+); bases donate hydroxide ions (OH–).
- Water is neutral with a pH of 7, very stable in its liquid form.
- Blood has a pH of approximately 7.4 (range: 7.35–7.45).
- Human stomach has a highly acidic pH (~2); small intestine is basic (pH 8–8.4).
- Buffers help maintain stable pH in most body tissues outside the stomach/intestine.
Carbohydrates and Sugars
- Carbohydrates include individual sugars (monosaccharides) such as glucose, fructose, and galactose.
- Disaccharides are formed by combining two monosaccharides (e.g., glucose + galactose = lactose, glucose + fructose = sucrose).
- Maltose is formed by two glucose molecules; many together form maltodextrin.
- Galactose is found in milk sugar (lactose).
Key Terms & Definitions
- Polar molecule — a molecule with uneven distribution of charge, leading to partial positive and negative areas.
- Hydrogen bond — a weak bond between molecules due to attraction between partial charges.
- Surface tension — the force at the surface of a liquid caused by molecular attraction.
- Surfactant — a substance that reduces surface tension, especially important in lung function.
- Acid — a substance that donates hydrogen ions (H+).
- Base — a substance that donates hydroxide ions (OH–).
- Buffer — a system that maintains stable pH in a solution.
- Monosaccharide — a single sugar molecule (e.g., glucose).
- Disaccharide — two monosaccharides bonded together (e.g., sucrose, lactose).
Action Items / Next Steps
- Review the properties and significance of water in biological systems.
- Memorize normal pH values for blood, stomach, and small intestine.
- Study common monosaccharides and disaccharides and their roles in metabolism.