Macromolecules are large biomolecules with molecular weights greater than ~10,000 Daltons. They are formed by polymerization of small monomers.

Four major classes:

• Proteins — polymers of amino acids. e.g., albumin, haemoglobin, collagen.
• Polysaccharides — polymers of monosaccharides. e.g., starch, cellulose, glycogen, chitin.
• Nucleic acids — polymers of nucleotides. e.g., DNA, RNA.
• Lipids (operationally) — in the acid-insoluble pool though molecularly small; e.g., membrane lipids in vesicles.

Glycosidic bond: Formed between —OH of one sugar's anomeric carbon and —OH of another sugar (or another molecule). Loss of one H₂O.

Sugar1—O—Sugar2 (with loss of H₂O)
e.g., Glucose + Fructose → Sucrose + H₂O (α-1,2 glycosidic bond)

Peptide bond: Formed between —COOH of one amino acid and —NH₂ of next. Loss of one H₂O.

R₁—CH(NH₂)—CO—NH—CH(R₂)—COOH
The —C(=O)—NH— group is the peptide bond.

Phosphodiester bond: Phosphate links 3'-OH of one nucleotide sugar to 5'-OH of next. Two ester linkages share one phosphate.

Nucleotide-1 (3'-OH) — O — PO₂⁻ — O — (5') Nucleotide-2
Forms the sugar-phosphate backbone of DNA/RNA.

Tertiary structure is the overall three-dimensional folding of a single polypeptide chain — how the entire chain (its α-helices, β-sheets, and connecting loops) packs in space to form a compact globular or fibrous shape.

Stabilising bonds:

• Hydrogen bonds (between R-groups)
• Ionic / salt bridges (between oppositely charged side chains)
• Disulphide bridges (covalent —S—S— between cysteine residues)
• Hydrophobic interactions (non-polar R-groups cluster inside, away from water)
• Van der Waals forces

Importance: The tertiary structure positions the active-site residues of an enzyme — without correct folding, the protein has no function. Example: myoglobin's tertiary fold creates the haem-binding pocket that lets it carry oxygen.

Molecule	Brief Structure	Industry Use
Citric acid	HOOC-CH₂-C(OH)(COOH)-CH₂-COOH	Soft-drink, food preservation
Lactic acid	CH₃-CHOH-COOH	Dairy (curd), biopolymer PLA
Acetic acid	CH₃-COOH	Vinegar, textile
Ethanol	CH₃-CH₂-OH	Beverages, fuel, sanitizer
Glucose	C₆H₁₂O₆ (aldohexose)	IV drips, fermentation
Caffeine	Methylated xanthine alkaloid	Beverages, pharma
Nicotine	Pyridine + pyrrolidine alkaloid	Pesticides, tobacco
Adrenaline	Catecholamine	Anaphylaxis drug
Penicillin	β-lactam ring + side chain	Antibiotic industry
Vitamin C (ascorbate)	C₆H₈O₆ lactone	Food/supplement industry

Industries: Pharmaceutical, food, beverage, cosmetics, fermentation — all rely on isolating and purifying these small biomolecules.

YES — knowing terminal amino acids is a powerful test for protein purity.

A pure protein is a homogeneous population — all molecules have identical sequences, hence the SAME amino acid at N-terminus and the SAME amino acid at C-terminus.

Test logic:

• If N-terminus analysis (e.g., Edman degradation) gives ONE unique amino acid → likely pure.
• If you find MULTIPLE different amino acids at "the" N-terminus → the sample contains multiple different proteins → impure / heterogeneous.
• Same logic for C-terminus (by carboxypeptidase digestion).

Caveat: Some proteins have N-terminal blocking modifications (acetylation, pyroglutamate) — sequencing might fail even though pure. Modern techniques use mass spectrometry which sidesteps this.

This is exactly how Frederick Sanger first proved insulin was a pure protein, then sequenced it (Nobel 1958).

Therapeutic Proteins:

• Insulin — diabetes treatment (recombinant human insulin since 1982)
• Growth hormone (GH) — for growth disorders
• Erythropoietin (EPO) — stimulates RBC production in anaemia, kidney disease
• Interferons — antiviral and cancer treatment
• Monoclonal antibodies — Herceptin (breast cancer), Rituximab (lymphoma), Humira (rheumatoid arthritis)
• Clotting factors VIII, IX — haemophilia treatment
• Tissue plasminogen activator (tPA) — for stroke
• Vaccines — hepatitis B surface antigen, COVID spike protein-based vaccines

Cosmetic / Industrial proteins:

• Collagen — anti-aging cream, wound dressings
• Keratin — hair care products
• Silk fibroin — luxury textiles, biomedical sutures
• Casein — adhesives, food fortifier
• Enzymes — protease in detergents, rennet in cheese, amylase in baking
• Botox — botulinum toxin (a neurotoxic protein) for cosmetic wrinkle removal

A triglyceride = 1 molecule of glycerol + 3 molecules of fatty acids, joined by three ester bonds (with release of 3 water molecules).

Structure:

H₂C—O—CO—R₁
 |
HC—O—CO—R₂
 |
H₂C—O—CO—R₃

where R₁, R₂, R₃ = long hydrocarbon chains of fatty acids (often C₁₄–C₂₀).

Saturated: all R chains have only single C—C bonds → solid at room temperature (animal fats like butter, ghee).
Unsaturated: one or more C=C double bonds → liquid at room temperature (plant oils like mustard oil, olive oil).

Function: Most concentrated form of energy storage in animals (adipose tissue) — yields ~9 kcal/g vs 4 kcal/g for carbs/proteins.

Milk → Curd: A case of bacterial fermentation + protein denaturation.

1. Milk contains the protein casein (~80% of milk protein) suspended as micelles, stabilized at neutral pH.
2. When a starter culture (Lactobacillus) is added, the bacteria ferment milk sugar (lactose) into lactic acid.
3. Lactic acid lowers the pH of milk from ~6.7 to ~4.6 (the isoelectric pH of casein).
4. At isoelectric pH, casein micelles lose their net surface charge → they no longer repel each other → they aggregate / coagulate.
5. The resulting gel network traps water, fat globules, and other components → semi-solid curd.

Key insight: This is acid-induced denaturation/coagulation of casein. It's the same principle by which paneer is made (using lemon juice or vinegar — direct acid addition without bacterial fermentation).

Bonus: Yoghurt also has live Lactobacillus probiotics, and the fermentation generates flavour compounds and partially digests lactose — making yoghurt easier to digest than milk for lactose-intolerant individuals.

Yes! Recommended modelling activity:

1. Glucose: 6 C atoms with H, OH groups; ring form has O in ring.
2. Amino acid (glycine): central C, with —NH₂, —COOH, —H, —H. Then alanine: replace one H with —CH₃.
3. Dipeptide: Link two amino acids by losing H₂O, forming —C(=O)—NH— bond.
4. Watson-Crick base pair: Adenine paired with thymine using 2 H-bonds (dotted lines between N-H...N and N...N-H).
5. Fatty acid: Long C chain (e.g., 16 C for palmitic) with —COOH at one end.

Online alternatives: Use JMol, RasMol, PyMOL, or AlphaFold for 3-D protein visualization. PDB (Protein Data Bank, rcsb.org) has free atomic models of thousands of proteins.

Acid-base titration of an amino acid:

1. Start with glycine at low pH (~1.5) — fully protonated form: ⁺H₃N-CH₂-COOH.
2. Add base (NaOH) slowly while measuring pH.
3. Plot pH vs equivalents of base added.

Observation: Plateaus appear at two pH values for glycine:

• pKa₁ ≈ 2.3 — the —COOH deprotonates to —COO⁻ (carboxyl group).
• pKa₂ ≈ 9.6 — the —NH₃⁺ deprotonates to —NH₂ (amino group).

Between the two plateaus is the isoelectric point (pI) — for glycine, pI = (2.3 + 9.6)/2 ≈ 5.97 — where it exists as a zwitterion with net zero charge.

Number of ionisable groups in glycine = 2 (—COOH and —NH₃⁺). Glutamate or aspartate would show 3 plateaus (one extra side-chain —COOH); lysine would show 3 plateaus (one extra side-chain —NH₃⁺).

Alanine structure (L-alanine):

       H
       |
  H₂N—C—COOH
       |
      CH₃

- Central α-carbon (chiral)
- —NH₂ amino group
- —COOH carboxyl group
- —H
- —CH₃ (methyl R-group) — making alanine the simplest "non-trivial" amino acid (glycine has R=H).

At physiological pH 7.4, alanine exists as zwitterion: ⁺H₃N-CH(CH₃)-COO⁻. R-group character: non-polar (hydrophobic). Code: A (one-letter) or Ala (three-letter). Non-essential — synthesized from pyruvate by transamination.

Natural gums are secondary metabolites — complex polysaccharides exuded by plants (often as defence/wound healing).

• Gum arabic (from Acacia) — a branched polysaccharide of D-galactose, L-arabinose, L-rhamnose, and glucuronic acid.
• Gum tragacanth (from Astragalus) — a mixture of polysaccharides including tragacanthic acid.
• Guar gum (from guar bean) — galactomannan.

Fevicol is DIFFERENT. It is a synthetic adhesive — specifically a polyvinyl acetate (PVA) emulsion in water. PVA is a synthetic polymer made by polymerization of vinyl acetate monomers, not a natural polysaccharide. So:

• Natural gums = biological polysaccharides (sugar polymers).
• Fevicol = man-made plastic emulsion (vinyl polymer).

Both stick things, but their chemistry and origin are fundamentally different.

Standard analytical procedures:

1. Total carbohydrates: Anthrone test (anthrone + conc. H₂SO₄ → blue-green colour proportional to sugars). Measure absorbance at 620 nm. Compare with glucose standard curve.
2. Reducing sugars: Benedict's test (quantitative if using DNS — dinitrosalicylic acid reagent). Read absorbance at 540 nm.
3. Proteins:
   • Kjeldahl method — measures total nitrogen × 6.25 = crude protein.
   • Biuret method — Cu²⁺ in alkali binds peptide bonds → purple colour at 540 nm.
   • Lowry / Bradford — for higher sensitivity.
4. Fats:
   • Soxhlet extraction — repeatedly extract food in petroleum ether/hexane → evaporate solvent → weigh residue (total lipid).
   • Sudan III / IV staining — qualitative.

Quantitative analysis example for rice (per 100 g):

• Carbohydrates ≈ 78 g (mostly starch)
• Proteins ≈ 7 g
• Fats ≈ 1 g
• Total calories = (78×4) + (7×4) + (1×9) = 312 + 28 + 9 ≈ 349 kcal