Week 1 Lecture 2B: Chemistry for Biologists

Water: The Most Important Molecule for Life

  • Water is recognized as the most crucial biological solvent necessary for life on Earth.

  • It consists of two hydrogen atoms covalently bonded to one oxygen atom, forming a polar molecule.

Chemical Structure of Water

  • Covalent Bonds: Water's hydrogen and oxygen atoms share electrons, resulting in a polarity where:

    • Oxygen ends up slightly negative (electro-negative).

    • Hydrogen ends up slightly positive (electro-positive).

  • Dipole Nature: The arrangement creates a dipole in water, meaning one end (hydrogen) is positive while the oxygen end is negative.

Intermolecular Interactions

  • Hydrogen Bonds: Water molecules attract each other via hydrogen bonds due to their polar nature.

    • Each water molecule can form hydrogen bonds with several surrounding water molecules.

    • These bonds contribute to water's unique properties such as surface tension and capillary action.

    • Example: Water's ability to move from roots to leaves in trees via evaporation is due to water's cohesive properties.

Behavior of Water in Different States

  • In liquid form, water molecules are in constant motion, forming and breaking hydrogen bonds quickly.

  • When energy is added (heating), water transitions to steam as molecules move apart.

  • When energy is removed (cooling), water forms a solid lattice structure known as ice, which has different properties than liquid water.

Interaction with Other Polar Molecules

  • Other polar molecules (like ammonia and hydrochloric acid) can form dipole-dipole interactions similar to water.

  • This ability to form hydrogen bonds allows other macromolecules to dissolve in water and participate in biological processes.

Types of Chemical Bonds in Biological Molecules

  • Biological macromolecules contain various types of chemical bonds:

    1. Covalent Bonds: Strong bonds that link atoms and molecules together.

    2. Ionic Bonds: Connections formed when atoms with opposite charges attract each other; these are generally stronger than hydrogen bonds.

    3. Hydrogen Bonds: Weaker bonds formed between polar molecules.

    4. Van der Waals Forces: Weak attractions that occur between neutral atoms or molecules at close distances.

Solubility and Macromolecules

  • Water as a solvent allows macromolecules (like proteins) to dissolve, facilitating myriad biological processes.

  • Solubility: A substance's ability to mix with water often relates to its polar or charged nature.

Concentrations and Molarity

  • Understanding concentrations of solutions is crucial in biological and laboratory contexts.

  • Mole: Defined as 6.02 x 10²³ particles (atoms, molecules, etc.).

  • Solutions are often expressed in molarity (M), which indicates moles per liter.

Ionization of Water

  • Water can self-ionize producing hydronium (H3O+) and hydroxide (OH-) ions, relevant for acidity and basicity in biological systems.

Chemistry of Organic Molecules

  • Organic Molecules: Contain carbon and are essential for life.

  • Polymers vs. Monomers:

    • Monomer: Small units (like amino acids).

    • Polymer: Chains of monomers (like proteins, nucleic acids, carbohydrates).

  • Examples of major organic compounds: carbohydrates, proteins, nucleic acids, and lipids.

Functional Groups in Organic Chemistry

  • Functional groups like amines, alcohols, and carboxylic acids greatly influence chemical reactivity and properties of organic molecules.

Summary of Important Concepts

  • Water’s unique properties support life and biological functions via its chemical structure and bonding characteristics.

  • The molecular interactions of water with macromolecules and ions are fundamental for biological processes.

  • A strong understanding of concentrations and chemical bonds is essential for studying biology and chemistry.

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