Biology: Class 12 — Chapter 10: Biotechnology and Its Applications

Traditional breeding failed to keep pace with demand, leading to the development of tissue culture.

• Explants: Any part of a plant taken out and grown in a test tube under sterile conditions in special nutrient media.
• Totipotency: The capacity to generate a whole plant from any cell or explant.
• Micro-propagation: The method of producing thousands of plants through tissue culture in very short durations.
• Somaclones: Plants genetically identical to the original plant (e.g., tomato, banana, apple).
• Somatic Hybridisation: Fusion of isolated naked protoplasts from two different varieties of plants to form somatic hybrids (e.g., pomato).

Plants, bacteria, fungi, and animals whose genes have been altered by manipulation are called Genetically Modified Organisms (GMO).

GM plants are useful because they:

• Increase tolerance to abiotic stresses (cold, drought, salt, heat).
• Reduce reliance on chemical pesticides (pest-resistant crops).
• Help reduce post-harvest losses.
• Increase efficiency of mineral usage by plants.
• Enhance nutritional value of food (e.g., Golden Rice, which is Vitamin A enriched).

Bt toxin is produced by the bacterium Bacillus thuringiensis. The gene has been cloned and expressed in plants to provide resistance to insects without insecticides.

• Target Insects: Lepidopterans (tobacco budworm, armyworm), coleopterans (beetles), and dipterans (flies, mosquitoes).
• Mechanism: The Bt toxin protein exists as inactive protoxins. Once ingested by an insect, the alkaline pH of the gut solubilises the crystals, converting them into an active form. The activated toxin binds to midgut epithelial cells, creating pores that cause swelling, lysis, and death.
• Genes: Coded by cry genes. cryIAc and cryIIAb control cotton bollworms; cryIAb controls corn borer.

The nematode Meloidogyne incognitica infects the roots of tobacco plants, reducing yield.

• Strategy: RNA interference (RNAi), a method of cellular defense in all eukaryotes.
• Mechanism: Involves silencing of a specific mRNA due to a complementary double-stranded RNA (dsRNA) molecule that binds to and prevents translation.
• Vector: Agrobacterium vectors are used to introduce nematode-specific genes into the host plant, producing both sense and anti-sense RNA to form dsRNA.

Insulin consists of two short polypeptide chains: chain A and chain B, linked by disulfide bridges.

• Pro-hormone Processing: In mammals, insulin is synthesized as a pro-hormone containing an extra stretch called the C-peptide, which is removed during maturation.
• Production: In 1983, Eli Lilly prepared DNA sequences corresponding to A and B chains, introduced them into plasmids of Escherichia coli to produce insulin chains separately, and combined them by creating disulfide bonds.

Gene therapy is a collection of methods that allows correction of a gene defect diagnosed in a child or embryo.

• First Clinical Trial (1990): Conducted on a 4-year-old girl with adenosine deaminase (ADA) deficiency, caused by the deletion of the gene for ADA.
• Procedure: Lymphocytes from the patient's blood are grown in culture. A functional ADA cDNA is introduced using a retroviral vector, and the cells are returned to the patient. Requires periodic infusion unless embryonic marrow cells are used.

Conventional methods cannot detect diseases early. Recombinant DNA technology, PCR (Polymerase Chain Reaction), and ELISA (Enzyme-Linked Immunosorbent Assay) serve this purpose.

• PCR: Detects low concentrations of pathogens by amplifying nucleic acids (used for HIV and gene mutations in cancer).
• ELISA: Based on the principle of antigen-antibody interaction.