Q. 1) Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves because
(a) bacteria are resistant to the toxin
(b) toxin is immature
(c) toxin is inactive
(d) bacteria encloses toxin in a special sac
Ans: (c) Toxin is inactive.
[Note: Some strains of Bacillus thuringiensis produce proteins that kill certain insects. The protein crystals are formed during a particular phase of their growth. These crystals contain a toxic insecticidal protein, however, it doesn’t kill the Bacillus because Bt toxin exists as inactive protoxins but once an insect ingests the inactive toxin, it is converted into an active form of toxin. The activated toxin creates pores in the midgut after binding, causes cell swelling and lysis eventually leading to the death of the insect.]
Q. 2) What are transgenic bacteria? Illustrate using any one example.
Ans: Transgenic bacteria are genetically modified bacteria which have a foreign gene (transgene) inserted in them. These microbes are useful in the production of antibiotics, alcohol, steroids and enzymes which are commercially important biochemicals.
Example of transgenic bacteria:
Diabetes is a very common disease which requires administration of insulin at regular time intervals. Taking insulin produced from other sources like pancreas of cows and pigs slaughtered for food poses severe risks in terms of allergies, etc. This necessitated the need for a recombinant insulin molecule of human origin. Mature human insulin molecule is produced from a pro-hormone and consists of two short polypeptide chains called chain A and chain B, that are linked by disulphide bridges with a challenge to assemble them into a mature form. Now, this can be done by preparing two DNA sequences corresponding to A and B chains of human insulin and introduced them in plasmids of E.coli to produce insulin chains separately. These chains were extracted separately and combined by creating disulphide bonds to make active human insulin, ready for use by humans.
Q. 3) Compare and contrast the advantages and disadvantages of production of genetically modified crops.
Ans: The plants used in agriculture whose genes have been altered by genetic manipulation are called genetically modified crops (GM crops). The main aim of creating GM crops is introducing new traits which are not present naturally in the parental crop.
The advantages of the production of genetically modified crops are as follows:
- GM crops are more tolerant to abiotic stresses like cold, drought, salinity and heat.
- GM crops have reduced dependence on chemical pesticides (pest-resistant crops), thereby increasing productivity.
- GM crops have increased the efficiency of mineral usage by plants, thereby preventing early depletion of soil minerals.
- GM crops have enhanced nutritional food value e.g. golden rice which is enriched with vitamin A.
- The post-harvest loss is less in GM crops.
The disadvantages of GM crops are below:
- There have been many controversies associated with GM crops. No one has actually tested the effect of GM crops on the humankind.
- Genetically modified ingredients can cause cancer or new allergy outbreaks in humans e.g. genetically modified soya bean containing Brazilian nut protein caused allergies in humans and had to be withdrawn from production.
- The newer varieties are marketed in less developed countries mostly by developed countries, thus resulting in increased dependence of poor countries on the west.
- The insect-resistant crops affect the natural biodiversity of the area e.g. Bt-toxin produced in the modified crops affect the natural pollinators like bees.
Q. 4) What are Cry proteins? Name an organism that produces it. How has man exploited this protein to his benefit?
Ans: Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans, coleopterans and dipterans. These strains produce crystals containing a toxic insecticidal protein called Bt toxin. This protein is called Cry protein and is expressed by a gene named cry gene.
During sporulation, many Bt strains produce this crystal protein with insecticidal properties. Scientists exploited this property of crystal proteins for creating genetically modified crops such as Bt cotton, Bt potato, Bt brinjal, Bt tobacco. The cry gene expressing the insecticidal protein was genetically introduced in the parent crop, thus creating a genetically modified Bt crop where the toxin protein expressed by the cry gene acted as an insecticide.
Q. 5) What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency?
Ans: Gene therapy is an experimental technique that uses genes to treat or prevent genetic diseases. It either involves replacing a mutated gene that causes disease with a healthy copy of the gene or inactivating, or ‘knocking out’, a mutated gene that is functioning improperly in an individual or in an embryo.
The expression of the new gene or genes can alter the DNA or RNA transcript used to synthesize proteins and therefore, cure the disease. Gene therapy is still in the experimental stages and is not very widely used. The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency. Adenosine deaminase is important for the normal functioning of the immune system but the disorder is caused in the event of ADA gene deletion.
The lymphocytes from the blood of the patient were grown in a culture outside the body. A functional ADA cDNA was then introduced into these cultured lymphocytes by using a retroviral vector and reintroduced into the patient. Since these now carried a functional ADA gene, active adenosine deaminase enzyme was expressed thereby, giving temporary relief to the patient. Since these cells are not immortal, patients require the regular infusion of such genetically engineered lymphocytes.
Q. 6) Diagrammatically represent the experimental steps in cloning and expressing a human gene (say the gene for growth hormone) into a bacterium like E.coli.
Ans: (Diagram as given in NCERT textbook)
Q. 7) Can you suggest a method to remove oil (hydrocarbon) from seeds based on your understanding of rDNA technology and chemistry of oil?
Ans: Oil consists of glycerols and fatty acids. In order to develop oil-free seeds, one needs to derive a mechanism to silence or inactivate the gene responsible for the production of glycerol and fatty acids. Using rDNA technology the genetic material of an organism can be manipulated to obtain the desired results.
Thus, if one wants to get oil-free seeds, genes responsible for the expression of glycerol and fatty acids need to be silenced or inactivated by performing various methods.
Q. 8) Find out from internet about golden rice.
Ans:
The aim of producing golden rice was to produce a fortified food to be grown and consumed in areas with a shortage of dietary vitamin A. Vitamin A deficiency kills about hundreds and thousands of children under the age of 5 each year. Golden rice is a genetically modified variety of Oryza sativa rice.
It has been produced by genetic engineering in such a way that it biosynthesizes beta-carotene, a precursor of vitamin A, in the edible parts of rice. Golden rice differs from its parental strain by the addition of three beta-carotene biosynthesis genes. The scientific details of the rice were first published in journal Science in 2000. It was the product of an eight-year-long project by Dr. Ingo Potrykus of the Swiss Federal Institute of Technology and Dr. Peter Beyer of the University of Freiburg.
This was considered a major breakthrough in biotechnology as an entire biosynthetic pathway was altered by scientists. In 2005, a new variety called Golden Rice 2 was announced which produces up to 23 times more beta-carotene than the original golden rice. Although golden rice was developed as a tool to replace dietary supplement of vitamin A, it has met with significant opposition from environmental and anti-globalization activists.
Q. 9) Does our blood have proteases and nucleases?
Ans: No, our blood does not contain proteases and nucleases. In human beings, blood serum contains different types of protease inhibitors, which protect the blood proteins from being broken down by the action of proteases.
The enzyme, nucleases, catalyzes the hydrolysis of nucleic acids therefore it is absent in the blood.
Q. 10) Consult internet and find out how to make orally active protein pharmaceutical. What is the major problem to be encountered?
Ans:
The orally active protein pharmaceutical are those that can be taken through the oral route. To successfully administer orally active protein pharmaceutical, one needs to put the protein in the form of a tablet whose coating is not affected by the acidic gastric juices. This coating should dissolve only in the intestine, thus releasing the proteins in the intestine from where they can be absorbed by the villi.
However, the proteases present in the stomach like pepsin, trypsin and chymotrypsin will act on the orally active protein pharmaceutical and degrade it. The acid of the stomach will denature whatever is remaining after degradation. The major problem that lies with the development of protein-based pharmaceutical is the fragile nature of the protein and requirement of precise conditions, both in terms of structure as well as surrounding environment, to ensure its activity.