AP Biology Unit 1 – Chemistry of Life: Ultimate Study Notes

Chemistry Foundations

Atoms and Molecules

  • Atoms: Smallest unit of matter; composed of protons (+), neutrons (neutral), electrons (−)

  • Atomic number = protons

  • Mass number = protons + neutrons

Trick: Think “p+n = weight, e = tiny and light”

  • Isotopes: Same element, different neutrons

    • Example: Carbon-12 vs Carbon-14 (used in radiometric dating)

Chemical Bonds

  • Covalent – electrons shared; strongest bond in molecules

    • Polar covalent: unequal sharing → partial charges (e.g., H₂O)

    • Nonpolar covalent: equal sharing (e.g., O₂, CH₄)

  • Ionic – electrons transferred; forms charged ions (Na⁺ + Cl⁻ → NaCl)

  • Hydrogen bonds – weak attraction between H and electronegative atom; critical for water, DNA, proteins

  • Van der Waals interactions – weak, temporary attractions; important in protein folding

Trick: Hydrogen bonds are “stickers,” covalent bonds are “cement,” ionic bonds are “magnets.”

Water – The Molecule of Life

Why water is special

  • Polar → dissolves polar molecules

  • Cohesion → water sticks to itself (surface tension, transpiration pull in plants)

  • Adhesion → water sticks to other surfaces

  • High specific heat → resists temperature change

  • High heat of vaporization → evaporative cooling

  • Ice is less dense than liquid → floats, protects aquatic life

Trick: Think “CHAIS” → Cohesion, High Specific Heat, Adhesion, Ice floats, Solvent

Macromolecules

Carbohydrates

  • Function: Energy & structural support

  • Monomer: Monosaccharides (glucose, galactose, fructose)

  • Polymer: Polysaccharides

    • Starch → plant energy storage

    • Glycogen → animal energy storage

    • Cellulose → plant cell walls (fiber)

    • Chitin → fungal cell walls, insect exoskeleton

Trick: “Starch stores, Cellulose supports”

Lipids

  • Function: Energy storage, membranes, signaling

  • Types:

    • Triglycerides: glycerol + 3 fatty acids (fats/oils)

    • Phospholipids: cell membranes (hydrophilic head, hydrophobic tails)

    • Steroids: cholesterol, hormones (testosterone, estrogen)

Trick: Phospholipid bilayer = “heads out, tails in”

Proteins

  • Function: Enzymes, structure, transport, defense

  • Monomer: Amino acids (20 types)

  • Structure Levels:

    1. Primary – amino acid sequence

    2. Secondary – α-helix / β-sheet (hydrogen bonds)

    3. Tertiary – 3D folding (R-group interactions)

    4. Quaternary – multiple polypeptides

  • Examples:

    • Hemoglobin → quaternary structure carries O₂

    • Enzymes → catalyze reactions (e.g., lactase breaks down lactose)

Trick: “Shape = Function” → denature protein → loses function

Nucleic Acids

  • Monomer: Nucleotides → sugar + phosphate + nitrogenous base

  • Polymer: DNA & RNA

    • DNA → double helix, A-T, G-C

    • RNA → single strand, uses U instead of T

  • Function: Store and transfer genetic information; template for proteins

Trick: “DNA stays, RNA moves”

Functional Groups

  • Hydroxyl (-OH) → alcohol, polar

  • Carbonyl (C=O) → ketone/aldehyde

  • Carboxyl (-COOH) → acidic

  • Amino (-NH₂) → basic

  • Sulfhydryl (-SH) → disulfide bridges in proteins

  • Phosphate (-PO₄) → energy (ATP), DNA backbone

  • Methyl (-CH₃) → affects gene expression

Memory tip: Think “OH Can Carve Amazing Small Perfect Molecules”

Chemical Reactions in Biology

  • Dehydration synthesis: build polymers, remove water

  • Hydrolysis: break polymers, add water

  • Enzymes: biological catalysts, reduce activation energy

    • Denatured by extreme pH, temp, inhibitors

    • Example: Catalase converts H₂O₂ → H₂O + O₂

  • Oxidation - lose electron

  • Reduction - gain electron

Trick: Think “OIL RIG” “Oxidation is lose, Reduction is gain

pH and Buffers

  • Acid: H⁺ donor (pH < 7)

  • Base: H⁺ acceptor (pH > 7)

  • Buffer: stabilizes pH, e.g., bicarbonate in blood

Trick: Acid = Add H⁺, Base = Brings H⁺ down