Overview
This lecture recaps the critical chemistry concepts underlying life, focusing on water, atomic structure, and the four macromolecules—carbohydrates, proteins, lipids, and nucleic acids—essential for AP Biology Unit 1.
Foundations of Chemistry
- Life’s chemical processes depend on atoms, particularly elements like carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.
- Atoms consist of protons (positive), neutrons (neutral), and electrons (negative), with electrons driving chemical bonding.
- Metabolism is the total of all chemical reactions within an organism, including anabolic (building) and catabolic (breaking down) reactions.
Properties of Water
- Water (H₂O) is polar due to oxygen’s higher electronegativity, resulting in partial charges.
- Hydrogen bonds form between water molecules, enabling cohesion (water to water), adhesion (water to other substances), and surface tension.
- Water’s high specific heat and lower density as ice are due to hydrogen bonding.
Chemical Reactions in Biology
- Dehydration synthesis removes water to bond monomers into polymers.
- Hydrolysis adds water to break polymers into monomers.
Elements Essential to Life
- CHNOPS: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur are the key elements in biological molecules.
- Carbon’s four bonds allow for diverse structures (chains, branches, rings).
Biological Macromolecules
Proteins
- Proteins are polymers of amino acids joined by peptide bonds.
- Each amino acid has a central carbon bonded to a hydrogen, carboxyl group, amino group, and variable R group.
- Protein structure: primary (amino acid sequence), secondary (α-helix/β-sheet via hydrogen bonds), tertiary (3D folding by R group interactions), and quaternary (multiple polypeptides).
- Protein function depends on shape, affected by environment and denaturation.
- Membrane proteins aid in transport, recognition, communication, and enzymatic activity.
Carbohydrates
- Carbohydrates have a C:H:O ratio of 1:2:1 and consist of monosaccharide monomers joined by glycosidic linkages.
- Serve as cellular fuel (glucose) and structural components (cellulose in plants, chitin in animals).
- Polysaccharides like starch and glycogen store energy in plants and animals, respectively.
Lipids
- Lipids are nonpolar, hydrophobic molecules with lots of hydrogen relative to oxygen.
- Types include fats (energy storage), phospholipids (membranes), and steroids (signaling, membranes).
- Saturated fats have straight tails; unsaturated fats have kinks due to double bonds.
- Phospholipids form bilayers with hydrophilic heads and hydrophobic tails.
Nucleic Acids
- DNA and RNA are nucleic acids made of nucleotide monomers (pentose sugar, phosphate, nitrogenous base).
- DNA is double-stranded, antiparallel (5'→3' and 3'→5'), and stores genetic info.
- Nitrogenous bases: purines (adenine, guanine), pyrimidines (cytosine, thymine in DNA, uracil in RNA).
- Phosphodiester bonds link nucleotides in the backbone.
Key Terms & Definitions
- Polar molecule — a molecule with uneven charge distribution (e.g., water).
- Hydrogen bond — weak attraction between a hydrogen atom and a more electronegative atom.
- Dehydration synthesis — reaction joining monomers by removing water.
- Hydrolysis — reaction breaking polymers by adding water.
- Peptide bond — covalent bond linking amino acids in proteins.
- Glycosidic linkage — bond joining carbohydrate monomers.
- Phospholipid — lipid forming cell membranes with hydrophilic heads and hydrophobic tails.
- Phosphodiester bond — bond linking nucleotides in nucleic acids.
- Denaturation — loss of protein structure and function due to environmental changes.
Action Items / Next Steps
- Download and complete the AP Bio Unit 1 Ultimate Review Packet and study guide.
- Attempt all practice questions and guided notes before checking the answer key.
- Take the unit practice multiple-choice questions for immediate feedback.
- Prepare for Unit 2: Cell Structure and Function.