Meristematic tissue has rapidly dividing cells and usually lacks well-developed vascular connections through which viruses spread. Therefore, meristem culture can regenerate healthy, virus-free plants from infected plants. NCERT gives banana, sugarcane and potato as examples.
The apical or axillary meristem is best suited because it is generally free of virus even when the rest of the plant is infected.
In tissue culture, explants are grown under sterile conditions to regenerate whole plants. The plants produced are genetically identical to the original plant and are called somaclones. This allows rapid multiplication of desirable varieties.
Micropropagation can produce a large number of genetically identical plants in a short time.
For in vitro propagation, the explant must receive nutrients and hormones under sterile conditions. NCERT specifically lists sucrose, inorganic salts, vitamins, amino acids, auxins and cytokinins as medium components.
The medium contains a carbon source such as sucrose, inorganic salts, vitamins, amino acids and growth regulators such as auxins and cytokinins.
- a. bacteria are resistant to the toxin
- b. toxin is immature
- c. toxin is inactive
- d. bacteria encloses toxin in a special sac
Bt toxin exists in the bacterium as an inactive protoxin. When an insect ingests it, the alkaline pH of the insect gut solubilises the crystals and converts the protoxin into the active toxin.
(c) toxin is inactive.
In recombinant insulin production, DNA sequences coding for human insulin chains A and B are introduced into plasmids of E. coli. The bacteria express the chains separately, which are extracted and joined by disulphide bonds to form human insulin.
Transgenic bacteria are bacteria whose DNA has been genetically modified by introducing a foreign gene. An example is E. coli engineered to produce human insulin.
Advantages listed by NCERT include tolerance to cold, drought, salt and heat; pest resistance; lower chemical pesticide use; lower post-harvest losses; better mineral use; and improved nutritional value such as golden rice. Possible disadvantages include unpredictable effects when released into ecosystems, evolution of resistant pests, gene flow to wild relatives, concerns over food safety, and issues of patents, biopiracy and farmer dependence.
GM crops can increase stress tolerance, reduce pesticide use, reduce post-harvest losses, improve mineral-use efficiency and enhance nutrition, but they may raise ecological, health, ethical, patent and biodiversity concerns.
Bacillus thuringiensis produces crystalline Bt toxin proteins. Specific cry genes such as cryIAc and cryIIAb control cotton bollworms, while cryIAb controls corn borer. By inserting these genes into crop plants, the plants produce the toxin and resist target insect pests, reducing insecticide use.
Cry proteins are insecticidal proteins encoded by cry genes of Bacillus thuringiensis. Humans have used these genes to develop pest-resistant transgenic crops such as Bt cotton.
ADA deficiency is caused by deletion of the gene for adenosine deaminase, an enzyme essential for immune function. In the first clinical gene therapy approach, lymphocytes from the patient were cultured outside the body, functional ADA cDNA was inserted into them using a retroviral vector, and the modified cells were returned to the patient. Since these lymphocytes are not immortal, repeated infusions are needed. Introducing the functional gene into early embryonic marrow cells could give a permanent cure.
Gene therapy is a set of methods for correcting a diagnosed gene defect by introducing a functional gene into a person's cells or tissues. In ADA deficiency, functional ADA cDNA can be introduced into patient lymphocytes using a retroviral vector.
A text flow diagram is: human DNA with growth hormone gene -> restriction digestion -> gene of interest; plasmid vector -> restriction digestion -> open vector; gene + vector + DNA ligase -> recombinant plasmid; recombinant plasmid -> competent E. coli by transformation; transformed cells -> selection on marker medium; selected clone -> large-scale culture in bioreactor; expressed protein -> downstream processing and purification.
The steps are: isolate the human gene, cut the gene and plasmid vector with the same restriction enzyme, ligate the gene into the vector, transform competent E. coli, select recombinants, culture them and purify the expressed growth hormone.
Seed oils are lipids synthesised through specific metabolic enzymes. If the gene coding for a key enzyme of fatty-acid or triacylglycerol synthesis is identified, RNA interference or gene knockout can reduce its expression in developing seeds. This would reduce oil formation. The exact target gene would depend on the crop and oil pathway.
One possible method is to use rDNA technology to silence or disrupt genes for enzymes required in oil biosynthesis in seeds, thereby lowering oil accumulation.
The chapter mentions golden rice as vitamin A enriched rice. It was engineered by introducing genes that enable beta-carotene synthesis in the rice endosperm, giving the grain a golden-yellow colour and helping address vitamin A deficiency.
Golden rice is genetically modified rice enriched with provitamin A, beta-carotene, in the edible grain.
Proteases such as thrombin and plasmin function in blood clotting and clot breakdown. Nucleases capable of degrading extracellular nucleic acids are also present in plasma and cells. These enzymes are controlled so they do not damage normal tissues or essential molecules indiscriminately.
Yes. Blood contains proteases involved in processes such as clotting and fibrinolysis, and it also contains nucleases, though their activity is regulated.
Proteins taken orally are usually denatured in the stomach and hydrolysed by proteases in the digestive tract. Even if protected, their large size and hydrophilic nature make intestinal absorption difficult. Therefore oral protein drugs require protective delivery systems and absorption-enhancing strategies.
Orally active protein pharmaceuticals may be made by protecting the protein in special coatings, nanoparticles, capsules or chemical modifications that help it survive digestion and be absorbed. The major problem is degradation by stomach acid and digestive proteases, along with poor absorption across the intestinal wall.