IASNOVA
AGRICULTURE
3 options to increase food production-
- Agro chemical based agriculture
- Organic agriculture
- Genetically engineered crop-based agriculture
Genetically Modified Organisms(GMOs)
Plants, Bacteria, Fungi, and Animals whose genes have been altered by manipulation are called Genetically Modified Organisms.
Advantages of GM crops-
- More tolerant to abiotic stress – cold,drought, heat, salt
- Reduced reliance on chemical pesticides- eg- Bt crops
- Reduced post harvest losses
- Increased efficiency of mineral usage by plants
- Enhanced nutritional value of food- eg- Vitamin A enriched rice
Pest resistant plants can reduce use of pesticides.Bt toxin is produced by a bacterium called Bacillus thuringiensis(Bt).This gene has been cloned from the bacteria and been exposed in plants to provide resistance to insecticides.
Examples- Bt cotton, Bt corn, Bt rice, tomato,potato,soyabean etc
Bt Cotton
Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes).
B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein.
Why does this toxin not kill the Bacillus?
Actually, the Bt toxin protein exist as inactive protoxins but once an insect ingest the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut which solubilise the crystals.
The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually cause death of the insect.
Most Bt toxins are insect-group specific. The toxin is coded by a gene cryIAc named cry. There are a number of them, for example, the proteins encoded by the genes cryIAc and cryIIAb control the cotton bollworms,that of cryIAb controls corn borer.
Pest Resistant Plants:
Several nematodes parasitise a wide variety of plants and animals including human beings. A nematode Meloidegyne incognitia infects the roots of tobacco plants and causes a great reduction in yield.
To prevent this infestation – process of RNA interference (RNAi).
RNAi takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA (silencing). The source of this complementary RNA could be from an infection by viruses having RNA genomes or mobile genetic elements (transposons) that replicate via an RNA intermediate.
Using Agrobacterium vectors, nematode-specific genes were introduced into the host plant .The introduction of DNA was such that it produced both sense and anti-sense RNA in the host cells. These two RNA’s being complementary to each other formed a double stranded (dsRNA) that initiated RNAi and thus, silenced the specific mRNA of the nematode. The consequence was that the parasite could not survive in a transgenic host expressing specific interfering RNA. The transgenic plant therefore got itself protected from the parasite.
BIOTECHNOLOGICAL APPLICATIONS IN MEDICINE
Recombinant DNA technological processes – enable mass production of safe and more effective therapeutic drugs.
The recombinant therapeutics do not induce unwanted immunological responses .
Genetically Engineered Insulin
Insulin used for diabetes was earlier extracted from pancreas of slaughtered cattle and pigs– but it caused allergy or other reactions in some patients.
Insulin consists of two short polypeptide chains: chain A and chain B, that are linked together by disulphide bridges .
In mammals, including humans, insulin is synthesised as a pro-hormone (like a pro-enzyme, the pro-hormone also needs to be processed before it becomes a fully mature and functional hormone) which contains an extra stretch called the C peptide. This C peptide is not present in the mature insulin and is removed during maturation into insulin.
The main challenge for production of insulin using rDNA techniques was getting insulin assembled into a mature form. In 1983, Eli Lilly an American company prepared two DNA sequences corresponding to A and B, chains of human insulin and introduced them in plasmids of E. coli to produce insulin chains. Chains A and B were produced separately, extracted and combined by creating disulfide bonds to form human insulin.
Gene Therapy
Gene therapy is a collection of methods that allows correction of a gene defect that has been diagnosed in a child/embryo. Here genes are inserted into a person’s cells and tissues to treat a disease. Correction of a genetic defect involves delivery of a normal gene into the individual or embryo to take over the function of and compensate for the non-functional gene.
The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency. This enzyme is crucial for the immune system to function. The disorder is caused due to the deletion of the gene for adenosine deaminase. In some children ADA deficiency can be cured by bone marrow transplantation; in others it can be treated by enzyme replacement therapy, in which functional ADA is given to the patient by injection. But the problem with both of these approaches that they are not completely curative. As a first step towards gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body. A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes, which are subsequently returned to the patient. However, as these cells are not immortal, the patient requires periodic infusion of such genetically engineered lymphocytes. However, if the gene isolate from marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure.
Molecular Diagnosis
Using conventional methods of diagnosis (serum and urine analysis, etc.) early detection is not possible.
Early Diagnosis can be done through-
- Recombinant DNA technology,
- Polymerase Chain Reaction (PCR) and
- Enzyme Linked Immuno-sorbent Assay (ELISA)
Presence of a pathogen (bacteria, viruses, etc.) is normally suspected only when the pathogen has produced a disease symptom. By this time the concentration of pathogen is already very high in the body. However, very low concentration of a bacteria or virus (at a time when the symptoms of the disease are not yet visible) can be detected by amplification of their nucleic acid by PCR.
PCR is now routinely used to detect HIV in suspected AIDS patients. It is being used to detect mutations in genes in suspected cancer patients too. It is a powerful techqnique to identify many other genetic disorders.
A single stranded DNA or RNA, tagged with a radioactive molecule (probe) is allowed to hybridise to its complementary DNA in a clone of cells followed by detection using autoradiography. The clone having the mutated gene will hence not appear on the photographic film, because the probe will not have complementarity with the mutated gene.
ELISA is based on the principle of antigen-antibody interaction. Infection by pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc.) or by detecting the antibodies synthesised against the pathogen.
TRANSGENIC ANIMALS
Animals that have had their DNA manipulated to possess and express an extra (foreign) gene are known as transgenic animals.
Transgenic rats, rabbits, pigs, sheep, cows and fish have been produced, although over 95 per cent of all existing transgenic animals are mice.
Advantages of Transgenic Animals-
- Transgenic animals can be specifically designed to allow the study of how genes are regulated, and how they affect the normal functions of the body and its development, e.g., study of complex factors involved in growth such as insulin-like growth factor.
- Many transgenic animals are designed to increase our understanding of how genes contribute to the development of disease. Today transgenic models exist for many human diseases such as cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer’s.
- Medicines required to treat certain human diseases can contain biological products, but such products are often expensive to make. Transgenic animals that produce useful biological products can be created by the introduction of the portion of DNA (or genes) which codes for a particular product such as human protein (α-1-antitrypsin) used to treat emphysema. Similar attempts are being made for treatment of phenylketonuria (PKU) and cystic fibrosis. In 1997, the first transgenic cow, Rosie, produced human protein-enriched milk (2.4 grams per litre). The milk contained the human alpha-lactalbumin and was nutritionally a more balanced product for human babies than natural cow-milk.
- Transgenic mice are being developed for use in testing the safety of vaccines before they are used on humans.
- Toxicity/safety testing- Transgenic animals are made that carry genes which make them more sensitive to toxic substances than non-transgenic animals. They are then exposed to the toxic substances and the effects studied. Toxicity testing in such animals will allow us to obtain results in less time.
ETHICAL ISSUES
Indian Government has set up organisations such as GEAC (Genetic Engineering Approval Committee), which will make decisions regarding the validity of GM research and the safety of introducing GM-organisms for public services.
Biopiracy is the term used to refer to the use of bio-resources by multinational companies and other organisations without prope authorisation from the countries and people concerned without compensatory payment.
