Unit 1 Hydrogen bond Tap / Space to flip
Unit 1 Weak attraction between δ⁺ H of one polar molecule and a δ⁻ atom (usually O, N, F) of another. Underlies water properties and DNA base pairing.
Unit 1 · 8–11% of exam
Chemistry of Life
Water properties, the four macromolecules, monomer/polymer relationships, and directionality. The foundation everything else builds on.
Must-know content
- Properties of water all stem from hydrogen bonding: cohesion, adhesion, surface tension, high specific heat, high heat of vaporization, ice less dense than liquid water, universal solvent. Polarity and capillary action drive transpiration in xylem.
- CHNOPS — the elements of life: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur.
- Four macromolecules — monomer, polymer, bond, function:
- Carbohydrates: monosaccharides → polysaccharides via glycosidic linkage (dehydration synthesis). Energy storage (starch, glycogen) and structure (cellulose, chitin).
- Lipids: not true polymers; glycerol + fatty acids → triglyceride via ester linkage. Phospholipids form bilayers; steroids include cholesterol. Saturated vs. unsaturated.
- Proteins: amino acids → polypeptides via peptide bonds. Four levels of structure (1° sequence, 2° α-helix/β-sheet via backbone H-bonds, 3° R-group interactions, 4° subunits). Function follows shape; denaturation by heat or pH disrupts higher-order structure.
- Nucleic acids: nucleotides → DNA/RNA via phosphodiester bonds. Antiparallel strands, 5′→3′ directionality.
- Directionality matters: proteins are synthesized N→C; nucleic acids are synthesized 5′→3′.
Example questions
MCQ Which property of water is MOST directly responsible for the upward movement of water in the xylem of a plant? (A) High specific heat (B) Cohesion and adhesion (C) Universal solvent ability (D) Lower density of ice
Answer: B. Cohesion (water-to-water H-bonds) maintains an unbroken column of water in the xylem; adhesion (water-to-xylem-wall) helps the column climb against gravity. Together they enable the transpiration-cohesion mechanism.
FRQ A researcher denatures an enzyme by heating it to 80 °C. Describe what happens to the enzyme's structure and explain why it loses function.
Answer: Heat disrupts the H-bonds, ionic bonds, and hydrophobic interactions that stabilize secondary, tertiary, and quaternary structure. Peptide bonds remain intact, so the primary sequence is preserved. The active site loses its specific 3-D shape, so substrate can no longer bind with the proper fit and catalysis ceases.
MCQ A 4-amino-acid peptide is built. Which type of bond connects the amino acids, and what byproduct is released? (A) Glycosidic, CO₂ (B) Peptide, H₂O (C) Ester, H₂O (D) Phosphodiester, H₂O
Answer: B. Peptide bonds form between adjacent amino acids by dehydration synthesis, releasing a water molecule per bond.
Drill flashcards
Unit 1 Cohesion vs. adhesion Tap / Space to flip
Unit 1 Cohesion = water-to-water; adhesion = water-to-other-substance. Together drive transpiration in xylem.
Unit 1 Dehydration synthesis Tap / Space to flip
Unit 1 Joins two monomers into a polymer; releases one H₂O molecule.
Unit 1 Hydrolysis Tap / Space to flip
Unit 1 Breaks a polymer using H₂O — reverse of dehydration synthesis.
Unit 1 Saturated fat Tap / Space to flip
Unit 1 No C=C double bonds; fatty-acid tails pack tightly; solid at room temperature.
Unit 1 Phospholipid bilayer Tap / Space to flip
Unit 1 Amphipathic phospholipids self-assemble with hydrophilic heads facing water and hydrophobic tails facing inward.
Unit 1 Primary structure (1°) Tap / Space to flip
Unit 1 Linear amino-acid sequence held together by peptide bonds. Determines all higher levels of folding.
Unit 1 Tertiary structure (3°) Tap / Space to flip
Unit 1 3-D fold from R-group interactions: H-bonds, ionic, hydrophobic, and disulfide bridges.