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.