Biological Chemistry and Water Properties

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Chemical Reactions and Bonds

  • Chemical Reactions: Making and breaking of chemical bonds.
    • Reactants: Starting molecules in a reaction.
    • Products: Final molecules after a reaction.
Photosynthesis Reaction
  • Important Chemical Reaction: Photosynthesis.
    • Process: Sunlight converts carbon dioxide $(6 ext{ CO}2)$ and water $(6 ext{ H}2O)$ into glucose $( ext{C}6 ext{H}{12} ext{O}6)$ and oxygen $(6 ext{ O}2)$.

Reversibility and Chemical Equilibrium

  • Reversibility: All chemical reactions can be reversed; products can become reactants in the reverse reaction.
  • Chemical Equilibrium: Reached when the rates of forward and reverse reactions are equal.

Properties of Water

  • Emergent Properties: Contribute to Earth's suitability for life:
    • Cohesion: Water molecules stick together due to hydrogen bonds.
    • Ability to Moderate Temperature: Requires significant energy to change temperature.
    • Expansion upon Freezing: Ice is less dense than water, causing it to float.
    • Versatility as a Solvent: Water can dissolve many substances.
Polarity of Water Molecule
  • Polar Nature: Oxygen has higher electronegativity than hydrogen.
    • Creates a partial negative charge on oxygen and a partial positive charge on hydrogen.

Water Chemistry and Organisms

  • Importance of Water: Essential for all living organisms due to unique properties derived from its molecular structure.
  • Hydrogen Bonds: The ability of water to form hydrogen bonds is its most important property.
Cohesion and Adhesion in Water
  • Cohesion: Water molecules are attracted to each other, aiding in water transport in plants.
  • Adhesion: Water molecules are attracted to other surfaces, helping resist gravity during water transport.

Temperature Moderation

  • High Specific Heat: Water absorbs a large amount of heat before changing temperature, enabling moderate ecosystems.
  • High Heat of Vaporization: Evaporation of water can cool surfaces, affecting climate.

Solvent Properties

  • Dissolution of Polar Molecules: Water can dissolve polar molecules and ions, making it crucial for biological functions.
    • Example: Sodium ions $( ext{Na}^+)$ and chloride ions $( ext{Cl}^-)$ are surrounded by water molecules (hydration shells).

Aqueous Solutions and Ions

  • **Definitions:
    • Aqueous Solution:** Water is the solvent.
    • Solute: Substance dissolved in a solution.
Ion Formation from Water
  • Water can ionize:
    ext{H}_2 ext{O}
    ightleftharpoons ext{OH}^- + ext{H}^+ ||

Acids and Bases

  • pH Scale: Measures hydrogen ion concentration.
    • Example:
    • Acids: Water below pH 7 (e.g., hydrochloric acid).
    • Bases: Water above pH 7 (e.g., sodium hydroxide).

Carbon and Molecular Diversity

  • Carbon's Properties:
    • Carbon can form diverse molecules by bonding to four different atoms (valence = 4).
    • Isomers: Compounds with the same molecular formula but different structures.
  • Types of Isomers:
    • Cis-Trans Isomers: Different spatial arrangements due to rigid double bonds.
    • Enantiomers: Mirror images, often with different biological activities.

Key Functional Groups in Biological Molecules

  • Importance of Functional Groups: Affect molecular functionality by participating in chemical reactions.
    • Common groups include: Hydroxyl, Carbonyl, Carboxyl, Amino, Sulfhydryl, Phosphate, and Methyl groups.

Monomers to Polymers

  • Formation of Polymers: Through dehydration reactions (loss of water) and hydrolysis (addition of water).
  • Lipids: Exception to monomer/polymer rules; triglycerides are a type of lipid polymer.

Carbohydrates and Their Function

  • Structure: Molecules with a 1:2:1 ratio of carbon, hydrogen, and oxygen (empirical formula: $( ext{C} ext{H}2 ext{O})n$).
    • Types of carbohydrates:
    • Monosaccharides (e.g., glucose) - simple sugars, important for energy storage.
    • Polysaccharides (e.g., starch, glycogen, cellulose) - complex carbohydrates for storage and structure.

Carbohydrate Reactions

  • Dehydration Reaction: Synthesis of disaccharides (e.g., maltose from glucose).
  • Glycosidic Linkages: Bonds formed between monosaccharides.
  • Structural Importance: Chitin and cellulose serve as structural components in organisms.