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Principles of Biochemistry Overview

  • Authors: Moran, Horton, Scrimgeour, Perry

  • Course: Biological Chemistry 400/644

  • Instructor: Professor Edward J. Kennelly

  • Chapter Focus: Water's crucial roles in biological systems.

Water and Life

  • Water accounts for 70% of biological systems.

  • Functions include serving as a solvent for chemical reactions, influencing protein structure, and participating in metabolic processes.

The Molecular Structure of Water

  • Polarity of Water: Oxygen is more electronegative than hydrogen, leading to a dipole with partial charges (O: neg, H: pos).

    • Water’s shape is V-like, with an angle of 104.5 degrees between hydrogen atoms.

  • Hydrogen Bonding: Water molecules form hydrogen bonds, which are essential for many of water’s unique properties like high specific heat and cohesion.

Physical Properties of Water

  • Specific Heat: Water has a high specific heat, meaning it can absorb a lot of heat without a significant temperature change. This property is crucial for temperature regulation in living organisms.

  • Heat of Vaporization: Evaporation of water requires substantial energy due to hydrogen bonds, making processes like sweating effective for temperature control.

Solubility and Interactions

  • Ionic and Polar Substances: Water can dissolve electrolytes (ions), while polar molecules tend to dissolve in water.

  • Hydrophobic Interactions: Nonpolar substances do not mix with water, leading to the "like dissolves like" principle.

Chemical Equilibria in Aqueous Solutions

  • Water can dissociate into hydronium (H3O+) and hydroxide ions (OH-). This leads to the concepts of acids and bases:

    • Acids: Proton donors (e.g., HCl).

    • Bases: Proton acceptors.

  • pH and pKa: The pH scale measures acidity; pKa relates to the strength of an acid in solution.

Acid-Base Chemistry in Biology

  • Biological buffers maintain pH stability in systems; for example, blood pH is regulated by bicarbonate ions and carbon dioxide.

  • Titration Curves: Help illustrate the dissociation of weak acids and bases, showing how buffer systems work within biological contexts.