Chapter summary
Biological molecules, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
Glucose isomers and glycosidic bonds
How can the same molecular formula produce different polymers?
Key idea and reminders
Alpha and beta glucose differ at carbon 1; the orientation of their glycosidic bonds changes the polymer built.
- Alpha/beta differ at carbon 1.
- Condensation forms a glycosidic bond and releases water.
- Hydrolysis consumes water to break the bond.
Keep in mind: They have the same composition; the arrangement around carbon 1 differs.
02
Starch, glycogen and cellulose
Why do storage and structural carbohydrates have different shapes?
Key idea and reminders
Alpha-glucose polymers store glucose compactly; beta-1,4 cellulose chains form strong microfibrils.
- Amylose: unbranched alpha-1,4 coil.
- Amylopectin and glycogen: alpha-1,6 branches.
- Cellulose: beta-1,4 straight chains and hydrogen-bonded microfibrils.
Keep in mind: Cellulose is unbranched; its beta-1,4 chains are strengthened by numerous interchain hydrogen bonds.
03
Triglycerides and phospholipids
Why does one lipid store energy while another builds a membrane?
Key idea and reminders
Triglycerides have three fatty acids and are largely hydrophobic; phospholipids have a polar head and two non-polar tails.
- Ester bond: glycerol to fatty acid.
- Triglyceride: three fatty-acid tails.
- Phospholipid: hydrophilic head and hydrophobic tails.
Keep in mind: Its tails are non-polar, but its polar head interacts with water; this contrast drives bilayer formation.
04
From amino acids to a folded protein
How does a sequence produce a specific three-dimensional shape?
Key idea and reminders
Amino-acid sequence constrains folding; different interactions stabilise secondary, tertiary and quaternary structures.
- Primary: sequence.
- Secondary: backbone hydrogen bonding.
- Tertiary: one chain; quaternary: multiple polypeptide subunits.
Keep in mind: A protein with one polypeptide may have no quaternary structure.
05
Why temperature and pH alter proteins
Why can a protein lose function without its chain being cut?
Key idea and reminders
Denaturation changes higher-level structure and function; it usually leaves the primary peptide sequence intact.
- High heat can disrupt folding.
- pH affects charge and interactions.
- Primary structure often survives denaturation.
Keep in mind: Moderate cooling usually lowers collision frequency and rate without permanently disrupting the protein.
06
Haemoglobin and collagen: shape for a job
Why is one protein soluble and the other a strong fibre?
Key idea and reminders
Haemoglobin uses a compact multi-subunit structure for reversible oxygen binding; collagen uses long associated chains and cross-links for tensile strength.
- Haemoglobin: four haem-bearing subunits.
- Oxygen binding is reversible and cooperative.
- Collagen: triple helix, fibrils and cross-links.
Keep in mind: Collagen has associated chains and higher-order fibrils; hydrogen bonds and intermolecular covalent cross-links contribute to strength.