What this chapter is about
This chapter explores how recombinant DNA technology and other biotechnological methods are used in medicine, agriculture, and industry to improve human life. After understanding the principles and processes of biotechnology in earlier chapters, students now learn the practical outcomes of these techniques in the real world.
The chapter covers three broad areas: biotechnological applications in agriculture (genetically modified crops, pest-resistant plants), applications in medicine (recombinant therapeutic proteins, gene therapy, molecular diagnostics), and transgenic animals. Students also encounter the ethical, legal, and social issues surrounding genetically modified organisms, including biosafety concerns and biopiracy.
By the end of this chapter, a Class 12 student should be able to explain how Bt crops resist pests, describe how insulin and other therapeutic proteins are produced using recombinant DNA technology, understand the principle behind gene therapy, and discuss the ethical considerations in biotechnology.
Key ideas
- Genetically Modified Organisms (GMOs) are organisms whose genetic material has been altered using recombinant DNA technology to introduce desirable traits such as pest resistance, herbicide tolerance, or improved nutritional content.
- Bt crops contain genes from the bacterium Bacillus thuringiensis that produce crystal proteins (Cry proteins) toxic to specific insect pests. The toxin becomes active only in the alkaline gut of insects, killing them without harming other organisms.
- RNA interference (RNAi) is a method to silence specific genes. It is used to create pest-resistant plants, such as those resistant to nematode attack, by introducing complementary RNA that forms double-stranded RNA and triggers degradation of pest mRNA.
- Recombinant human insulin is produced by inserting the human insulin gene into Escherichia coli bacteria, which then synthesise the protein. The A and B chains are produced separately and combined to form functional insulin.
- Gene therapy involves introducing a functional gene into cells of a patient to correct a genetic defect. The first clinical trial involved treatment of adenosine deaminase (ADA) deficiency using genetically modified lymphocytes.
- Molecular diagnostics use techniques such as Polymerase Chain Reaction (PCR) and Enzyme-Linked Immunosorbent Assay (ELISA) to detect pathogens or genetic disorders with high sensitivity and specificity.
- Transgenic animals are created by introducing foreign genes for purposes such as studying diseases, testing vaccines, producing biological products (like human proteins in milk), and testing drug safety.
- Bioethics and biosafety address concerns about environmental release of GMOs, potential health effects, and issues of biopiracy where traditional knowledge and biological resources are exploited without fair compensation.
Formulas and facts to remember
- Cry proteins: Encoded by cry genes from Bacillus thuringiensis; cry1Ac and cry2Ab control cotton bollworm; cry1Ab controls corn borer.
- Bt toxin mechanism: Inactive protoxin crystal → ingested by insect → solubilised in alkaline midgut → activated toxin → binds to gut epithelium → creates pores → cell swelling and lysis → insect death.
- Recombinant insulin production: Human insulin gene inserted into plasmid → transformed into E. coli → A chain and B chain produced separately → chains combined by disulphide bonds → functional human insulin.
- ADA deficiency treatment: Lymphocytes extracted from patient → functional ADA gene introduced using retroviral vector → modified lymphocytes reinfused into patient.
- PCR principle: Specific DNA sequences amplified using primers, DNA polymerase (Taq polymerase), and repeated cycles of denaturation, annealing, and extension.
- ELISA principle: Antibody-antigen interaction detected using enzyme-linked antibodies that produce a colour change with substrate.
- Golden Rice: Genetically modified rice containing genes for beta-carotene synthesis to address vitamin A deficiency.
- Biopiracy examples: Patenting of products based on traditional knowledge of plants like neem, turmeric, and basmati rice without acknowledging origin countries.
Worked examples
Example 1: Bt cotton and pest resistance
Problem: A farmer plants Bt cotton expressing the Cry1Ac protein. Explain the sequence of events when a cotton bollworm larva feeds on this plant.
Solution: Step 1: The Bt cotton cells contain the cry1Ac gene and produce Cry1Ac protein as inactive protoxin crystals.
Step 2: When the bollworm larva ingests the cotton leaf tissue, the protoxin crystals enter its midgut.
Step 3: The insect midgut is highly alkaline (pH around 9–10). This alkaline environment solubilises the crystal protein.
Step 4: Gut proteases cleave the protoxin, converting it into active Bt toxin.
Step 5: The active toxin binds to specific receptors on the midgut epithelial cells of the larva.
Step 6: This binding creates pores in the cell membrane, causing cells to swell due to osmotic imbalance.
Step 7: The gut lining is destroyed, leading to septicaemia and death of the larva within 2–3 days.
The plant remains unaffected because mammalian and other non-target organisms have neutral or acidic gut conditions where the toxin remains inactive.
Example 2: Gene therapy for ADA deficiency
Problem: A child is diagnosed with severe combined immunodeficiency (SCID) due to adenosine deaminase deficiency. Describe how gene therapy could help this patient.
Solution: Step 1: ADA is an enzyme essential for proper immune function. Its absence causes accumulation of toxic metabolites that destroy lymphocytes.
Step 2: Lymphocytes (white blood cells) are isolated from the patient's blood.
Step 3: A functional ADA gene is inserted into a retroviral vector. The vector is modified so it cannot cause disease.
Step 4: The patient's lymphocytes are infected with the recombinant retrovirus in culture. The virus integrates the ADA gene into the lymphocyte genome.
Step 5: These genetically corrected lymphocytes are grown in culture to increase their numbers.
Step 6: The modified lymphocytes are infused back into the patient's bloodstream.
Step 7: The corrected cells now produce functional ADA enzyme, partially restoring immune function.
Note: This treatment is not permanent because lymphocytes have a limited lifespan. Repeated infusions or correction of bone marrow stem cells may provide longer-lasting results.
Example 3: Using PCR for disease diagnosis
Problem: How can PCR help in early detection of HIV infection when antibody tests may give false negatives?
Solution: Step 1: In early HIV infection, the virus is present but antibody levels may be too low to detect by ELISA.
Step 2: PCR can amplify viral genetic material (HIV RNA or proviral DNA) present in even minute quantities.
Step 3: Specific primers complementary to conserved HIV gene sequences are designed.
Step 4: Patient's blood sample is processed to extract nucleic acids.
Step 5: PCR amplification is performed with repeated thermal cycles, exponentially increasing the target sequence.
Step 6: After 25–30 cycles, sufficient DNA is produced for detection by gel electrophoresis or probe-based methods.
Step 7: Presence of the amplified HIV sequence confirms infection, even during the window period when antibodies are undetectable.
This high sensitivity makes PCR valuable for screening blood donations and early diagnosis.
Common mistakes
- Thinking Bt toxin harms all organisms → the toxin is activated only in the alkaline gut of specific insects and is harmless to mammals, birds, and beneficial insects.
- Believing gene therapy provides permanent cure in all cases → many gene therapies require repeated treatments because modified cells may not persist or may not reach all affected tissues.
- Confusing Bt crops with pesticide-sprayed crops → Bt crops produce toxin internally; no external pesticide application is needed for the target pest.
- Assuming PCR can directly detect any disease → PCR detects specific nucleic acid sequences; the pathogen's genetic material must be known and appropriate primers designed.
- Thinking transgenic animals are created only for food production → major uses include disease models, vaccine testing, and production of therapeutic proteins, not primarily food.
Quick revision
- Bt toxin: inactive crystal → alkaline gut → active toxin → pores in gut → insect death.
- Recombinant insulin: separate A and B chains from E. coli joined by disulphide bonds.
- Gene therapy corrects genetic defects by introducing functional genes into patient cells.
- PCR amplifies specific DNA sequences for early and sensitive pathogen detection.
- RNAi silences genes using complementary RNA that triggers mRNA degradation.
- Biopiracy involves using traditional biological knowledge without permission or compensation.