Overview
This lecture reviews AP Biology Unit 1: The Chemistry of Life, covering macromolecules (carbohydrates, proteins, nucleic acids, lipids), water properties, and related concepts essential for understanding later units.
Macromolecules Overview
- Four main biological macromolecules: carbohydrates, proteins, nucleic acids, and lipids.
- Each macromolecule has distinct elements, monomers (except lipids), and functions.
- Recognizing structure, composition, and function is essential for AP Biology.
Carbohydrates
- Made of carbon, hydrogen, and oxygen in a 1:2:1 ratio (e.g., glucose: C6H12O6).
- Monomer: monosaccharide (e.g., glucose, fructose, galactose).
- Disaccharides form via dehydration reactions (e.g., sucrose, lactose, maltose).
- Polysaccharides serve structural (cellulose, chitin) or storage (starch, glycogen) roles.
- Glycosidic linkage bonds monosaccharides; animals can break alpha but not beta linkages.
Proteins
- Composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.
- Monomer: amino acid (central carbon, amino group, carboxyl group, R group).
- Peptide bonds form between amino acids via dehydration synthesis.
- Protein levels: primary (amino acid sequence), secondary (alpha helix, beta sheet; hydrogen bonds), tertiary (3D folding; R group interactions), quaternary (multiple polypeptides).
- R group properties (polar, nonpolar, charged) affect folding and solubility.
Nucleic Acids
- Contain carbon, hydrogen, oxygen, nitrogen, and phosphorus.
- Monomer: nucleotide (phosphate, pentose sugar, nitrogenous base).
- Bonds: phosphodiester linkage between nucleotides.
- DNA and RNA differ by sugar (deoxyribose vs ribose), bases (T in DNA, U in RNA), and strandedness (DNA double, RNA single).
- Purines (A, G) are double-ringed; pyrimidines (C, T, U) are single-ringed.
- Pairing: A-T/U (2 H bonds), C-G (3 H bonds); DNA is antiparallel (5’ to 3’).
Lipids
- Made mainly of carbon, hydrogen, and oxygen (few oxygens), sometimes phosphorus (phospholipids).
- No true monomer; types include fats (glycerol + 3 fatty acids), phospholipids (glycerol + phosphate + 2 fatty acids), and steroids (four fused rings).
- Saturated fats have single C-C bonds; unsaturated have at least one double bond (causing kinks).
- Phospholipids are amphipathic (hydrophilic head, hydrophobic tail) and form cell membranes.
- Steroids function as hormones and cell signaling molecules.
Water Properties
- Water is polar due to unequal sharing of electrons between O and H.
- Forms hydrogen bonds, leading to cohesion (water-water), adhesion (water-other surfaces), capillary action, and surface tension.
- Universal solvent: dissolves polar and ionic substances.
- High specific heat allows temperature regulation; ice is less dense than liquid water.
- Evaporative cooling helps organisms maintain stable temperatures.
- pH is determined by H+ concentration (pH = -log[H+]).
Example & Practice Questions
- Amino acids with nonpolar R groups are buried inside proteins; polar R groups are on the surface due to hydrophilic interactions.
- X-ray diffraction images of DNA support its helical structure.
- Glucose consists of carbon, hydrogen, and oxygen atoms with covalent bonds.
Key Terms & Definitions
- Monomer — basic building block of a polymer (e.g., amino acid, nucleotide, monosaccharide).
- Dehydration Reaction — forms bonds by removing water.
- Peptide Bond — covalent bond between amino acids.
- Glycosidic Linkage — covalent bond between carbohydrate monomers.
- Phosphodiester Linkage — bond connecting nucleotides in nucleic acids.
- Hydrogen Bond — weak attraction between polar molecules (e.g., between water molecules).
- Amphipathic — molecule with both hydrophobic and hydrophilic regions.
Action Items / Next Steps
- Review structure and function of all four macromolecules and water properties.
- Complete topic questions and FRQ practice from the provided review guide.
- Access AP Bio Penguins’ website and social media for additional resources and practice games.
- Attend upcoming live review sessions as scheduled.