Week 1 Lecture 2B: Chemistry for Biologists

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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.