🧬biochemistry review
1.2 Properties of Water and Its Biological Significance
Last Updated on August 9, 2024
Water is the foundation of life, shaping our world in countless ways. Its unique properties, from polarity to hydrogen bonding, make it essential for biological processes and ecosystems.
Understanding water's behavior is key to grasping biochemistry. We'll explore how its molecular structure influences its role as a solvent, temperature regulator, and driving force behind crucial biological interactions.
Molecular Interactions
Polarity and Hydrogen Bonding
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- Water molecules exhibit polarity due to uneven distribution of electrons
- Oxygen atom attracts electrons more strongly than hydrogen atoms
- Results in partial negative charge on oxygen and partial positive charges on hydrogens
- Polarity enables formation of hydrogen bonds between water molecules
- Hydrogen bonds form when partially positive hydrogen of one molecule attracts partially negative oxygen of another
- Hydrogen bonding gives water unique properties (high boiling point, surface tension)
Hydrophilic and Hydrophobic Interactions
- Hydrophilic substances readily interact with water molecules
- Includes polar molecules and ions (sugars, salts)
- Hydrophilic substances dissolve easily in water
- Hydrophobic substances repel water molecules
- Includes nonpolar molecules (oils, fats)
- Hydrophobic substances tend to cluster together in water
- Amphipathic molecules contain both hydrophilic and hydrophobic regions
- Phospholipids in cell membranes are amphipathic (hydrophilic head, hydrophobic tails)
- Amphipathic molecules can form structures like micelles and bilayers in water
Cohesive and Adhesive Properties
Cohesion and Surface Tension
- Cohesion refers to attraction between molecules of the same substance
- Water exhibits strong cohesion due to hydrogen bonding between water molecules
- Cohesion allows water to form droplets and beads on surfaces
- Surface tension results from cohesive forces at the water's surface
- Creates a "skin-like" layer on water's surface
- Allows some insects to walk on water (water striders)
- Enables formation of water droplets and meniscus in glass tubes
Adhesion and Capillary Action
- Adhesion describes attraction between different types of molecules
- Water molecules can adhere to other substances (glass, plant cell walls)
- Interplay between cohesion and adhesion leads to capillary action
- Capillary action allows water to move upward in narrow spaces against gravity
- Crucial for water transport in plants (xylem vessels)
- Enables water to be drawn up thin tubes in laboratory settings
Thermal and Solvent Properties
Specific Heat Capacity and Temperature Regulation
- Specific heat capacity measures energy required to raise temperature of a substance
- Water has unusually high specific heat capacity compared to other liquids
- Requires 4.184 joules to raise 1 gram of water by 1°C
- High specific heat capacity allows water to resist temperature changes
- Helps regulate temperature in living organisms and ecosystems
- Oceans act as heat sinks, moderating Earth's climate
- Human body uses water to maintain stable internal temperature
Universal Solvent Properties
- Water acts as a universal solvent due to its polarity and hydrogen bonding ability
- Dissolves more substances than any other liquid
- Polar and ionic compounds readily dissolve in water (salts, sugars, amino acids)
- Facilitates essential biochemical reactions in living organisms
- Enables transport of nutrients and waste products in biological systems
- Crucial for cellular processes (metabolism, signaling, enzyme function)
- Supports diverse aquatic ecosystems by dissolving oxygen and nutrients