Lecture Notes: Hydrophilic and Hydrophobic Molecules

Key Concepts

• Hydrophilic Molecules

  • "Hydro" means water, "philic" means loving.
  • These molecules love water and dissolve readily in water.
  • Typically have a positive or negative charge.
  • Examples include:
    • Ionic Compounds
      • E.g., Salt (NaCl) dissolves in water.
    • Polar Covalent Compounds
      • E.g., Water and ethanol are polar covalent compounds and dissolve in water.
  • Amino Acids
    • Biological molecules that are hydrophilic.
    • Have a polar nature with uneven charge distribution.
    • Dissolve in water, important for biological processes and metabolism.

• Hydrophobic Molecules

  • "Hydro" means water, "phobic" means fearing (or hating).
  • These molecules do not dissolve in water.
  • Typically nonpolar covalent compounds.
  • Even charge distribution.
  • Examples include:
    • Fats and Oils
      • Lipids are hydrophobic.
    • Steroids
      • Testosterone as an example.
      • Although may seem polar, behaves as nonpolar due to evenly distributed charges.

Important Principles

• Like Dissolves Like
  • Polar molecules dissolve in polar solvents (e.g., water).
  • Nonpolar molecules dissolve in nonpolar solvents (e.g., fats).

Biological Implications

• Understanding the hydrophilic and hydrophobic nature of molecules aids in explaining biological processes such as metabolism and transport of molecules in water-based environments.

Summary

• Water is a polar molecule.
• Molecules that are polar are hydrophilic and dissolve in water.
• Fats are nonpolar molecules.
• Molecules that are nonpolar are hydrophobic and do not dissolve in water.