Biomolecules and the Chemistry of Living Systems
What you must know
Life is built from a small set of monomer families: amino acids (proteins), nucleotides (nucleic acids), monosaccharides (carbohydrates), and fatty acids/glycerol (lipids). Know the functional groups (hydroxyl, carboxyl, amino, phosphate, sulfhydryl, carbonyl) and how they drive hydrogen bonding, polarity, and solubility. Understand the four levels of protein structure and the bonds stabilizing each: peptide bonds (covalent) in primary, backbone H-bonds in secondary (alpha helix, beta sheet), side-chain interactions in tertiary (hydrophobic, ionic, H-bond, disulfide), and subunit contacts in quaternary. For nucleic acids, know that DNA strands are antiparallel, A pairs with T (2 H-bonds) and G with C (3 H-bonds), and that base stacking plus H-bonding stabilize the duplex. For lipids, distinguish saturated (straight, tightly packed) from unsaturated (kinked, more fluid) fatty acids, and know that amphipathic phospholipids spontaneously form bilayers in water.
Traps
Questions often conflate covalent disulfide bonds with noncovalent tertiary interactions, or claim that denaturation breaks peptide bonds (it disrupts noncovalent structure, not primary sequence). Watch for wording about which bond type dominates a specific structural level. Also beware of assuming all lipids are hydrophobic-phospholipids are amphipathic.
Worked rule of thumb
When asked what stabilizes a structure, map the level to the bond: primary = peptide; secondary = backbone H-bonds; tertiary = side-chain contacts (including disulfides); quaternary = inter-subunit contacts. Apply this mapping before reading answer choices.
Quick example
A protein loses activity at high temperature but regains it on cooling. This indicates reversible denaturation of noncovalent interactions, not cleavage of peptide bonds-so the primary sequence is intact.