The complete lecture — the biomolecules of life come alive in the live panel as you read. Scroll down; the animation keeps pace, building a glucose ring, a peptide bond, a folding protein, an enzyme catching its substrate, and a DNA double helix.
1 — Biomolecules overview
- Biomolecule — a large molecule built by living cells. Most are polymers of small monomers, joined by removing water (condensation) and split by adding water (hydrolysis).
| Biomolecule | Monomer |
|---|
| Carbohydrate | monosaccharide |
| Protein | amino acid |
| Lipid | fatty acid + glycerol |
| Nucleic acid | nucleotide |
2 — Carbohydrates
- Carbohydrate — sugars & their polymers, Cₓ(H₂O)ᵧ. Classified as mono- (glucose), di- (sucrose) and polysaccharides (starch, cellulose, glycogen).
Glucose exists mostly as a six-membered ring. A reducing sugar (free –CHO) reduces blue Cu²⁺ to a brick-red precipitate in Benedict's test; sucrose is non-reducing.
3 — Polysaccharides
| Polymer | Role |
|---|
| Starch (α-glucose) | energy store in plants |
| Glycogen (branched) | energy store in animals |
| Cellulose (β-glucose) | structure — plant cell walls |
Humans cannot digest cellulose (the β-link) — it passes through as fibre.
4 — Proteins: amino acids & the peptide bond
- Amino acid — H₂N–CH(R)–COOH. Having both acid and base groups, it exists as a zwitterion (⁺H₃N–CH(R)–COO⁻).
Peptide bond–COOH + H₂N– → –CO–NH– + H₂O
5 — Protein structure & denaturation
- Primary — sequence of amino acids.
- Secondary — α-helix / β-pleated sheet (H-bonds).
- Tertiary — folded 3-D shape; Quaternary — several chains (haemoglobin).
Denaturation — heat or acid breaks the H-bonds, so the protein loses its shape and function (egg-white setting).
Tests: biuret → violet (peptide bonds); ninhydrin → blue-purple (amino groups).
6 — Lipids
- Triglyceride — glycerol + 3 fatty acids. Saturated (no C=C) → solid fats (ghee); unsaturated (C=C) → liquid oils.
Phospholipids have a water-loving head and water-hating tails; in water they form the bilayer that makes every cell membrane.
7 — Enzymes: biological catalysts
Lock-and-keyenzyme + substrate → enzyme-substrate → enzyme + products
Enzymes are protein catalysts. Only a substrate that fits the active site binds → specificity. Rate depends on temperature (optimum ~37 °C, then denatures), pH and substrate concentration. Move the sliders to see the rate respond.
8 — Factors affecting enzyme activity
| Factor | Effect |
|---|
| Temperature | rises to optimum (~37 °C), then denatures |
| pH | each has an optimum pH |
| [substrate] | rises then levels off (saturation) |
9 — Nucleic acids: DNA & RNA
- Nucleotide — sugar + phosphate + base. DNA = deoxyribose, double helix, bases A T G C; RNA = ribose, single strand, A U G C.
Base pairingA = T (2 H-bonds) · G ≡ C (3 H-bonds)
Complementary base pairing lets DNA copy itself exactly — the basis of heredity.
10 — Vitamins & worked questions
| Type | Examples |
|---|
| Fat-soluble | A, D, E, K (stored) |
| Water-soluble | B-complex, C (daily) |
peptide bond
–COOH + H₂N– → –CO–NH– + H₂O.
base pairing
Strand A–G–C–T pairs with T–C–G–A.
11 — Exam recap
- Four biomolecules & their monomers.
- Carbohydrates: glucose ring, reducing sugars, polysaccharides.
- Proteins: amino acids, the peptide bond, structure & denaturation.
- Lipids: triglycerides & the membrane bilayer.
- Enzymes: lock-and-key, specificity & factors.
- Nucleic acids: DNA, RNA & base pairing. Vitamins.