2.1 Recombinant Insulin
Human insulin has an A chain (21 aa) and B chain (30 aa) linked by disulfide bonds. Proinsulin contains an additional C peptide that is removed during maturation. Eli Lilly (1983) produced Humulin by cloning A and B chain genes separately into E. coli, expressing them independently, and assembling the chains chemically. This replaced allergenic animal-source insulin.
Why it matters for NEET: Questions test the number of amino acids in each chain, the role of the C peptide, and why E. coli rather than a single expression system was used (chains expressed separately to ensure correct disulfide bond formation).
2.2 Gene Therapy
Gene therapy corrects inherited disorders by introducing a functional gene copy. ADA deficiency was the first approved case. The retroviral vector delivers the functional ADA gene into isolated patient lymphocytes, which are then reinfused. Limitations: lymphocytes are non-immortal (repeated infusions needed); permanent cure requires bone marrow transplant. Interim treatment: PEG-ADA enzyme injections.
Why it matters for NEET: ADA deficiency, retroviral vectors, and the distinction between temporary (lymphocyte infusion) and permanent (bone marrow transplant) cure are all direct exam targets.
2.3 Molecular Diagnostics
Three key diagnostic tools:
- PCR — DNA amplification using Taq polymerase; detects pathogen DNA even before symptoms appear (early HIV, genetic disorders).
- ELISA — Enzyme-linked antibody detection; identifies antigens or antibodies; used for HIV, hepatitis B, pregnancy.
- Autoradiography — Radioactive probe hybridization on membranes; identifies specific DNA or RNA sequences.
2.4 Bt Crops
Bacillus thuringiensis produces crystalline Cry proteins (protoxins) that are inactive until ingested by susceptible insects. Alkaline gut pH activates the toxin, which binds midgut epithelial receptors, forms pores, causes lysis.
| Crop | Cry Genes | Target Pest |
|---|---|---|
| Bt cotton | cry1Ac, cry2Ab | Cotton bollworm (Helicoverpa) |
| Bt corn | cry1Ab | European corn borer (Ostrinia) |
2.5 RNA Interference (RNAi)
dsRNA introduced into cells triggers Dicer-mediated cleavage into siRNAs, which silence complementary mRNA via RISC. In tobacco engineered against Meloidogyne incognita (root-knot nematode), sense and antisense nematode-gene sequences produce dsRNA inside the pest, disabling it.
2.6 GM Crops and Food
- Golden Rice — beta-carotene produced in endosperm; addresses vitamin A deficiency.
- Flavr Savr tomato — antisense polygalacturonase gene; delayed fruit ripening; first approved GM food.
2.7 Transgenic Animals
Used for protein production (alpha-1-antitrypsin from sheep milk; human alpha-lactalbumin from Rosie the cow), disease modeling (cancer, Alzheimer's in mice), vaccine safety, and chemical toxicity testing.
2.8 Bioethics, GEAC, and Biopiracy
GEAC is India's statutory body for GMO approval. Biopiracy cases: neem (antifungal patent revoked), turmeric (wound-healing patent revoked after India proved prior art), basmati (RiceTec patent partially cancelled).