Very Short Answer Type Questions

Question. Suggest a molecular diagnostic procedure that detects HIV in suspected AIDS patients.
Answer : PCR and ELISA. 

Question. Mention the chemical change that proinsulin undergoes, to be able to act as mature insulin.
Answer : Removal of C-peptide (from pro-insulin).
Detailed Answer:
Insulin is synthesized as a pro-hormone, which needs to be processed before it becomes a fully mature and functional hormone. The pro-hormone is a single polypeptide chain with an extra stretch called the C-peptide. This is removed during maturation.

Question. Write the possible source of RNA interference (RNAi) gene. 
Answer : The source of RNA gene could be from an infection by viruses having RNA genomes or mobile genetic elements (transposons) that replicate via an RNA intermediate. 

Question. Biotechnologists refer to Agrobacterium tumefaciens as a natural genetic engineer of plants.
Give reasons in support of the statement.
Answer : Agrobacterium tumefaciens is referred to as the natural genetic engineer of plants because the genes which are carried by its plasmid bring out their effects in various parts of the plants. 

Question. What are Cry genes ? In which organism are they present ? 
Answer : The genes which code for Bt toxin / Cry proteins (toxic proteins), Bacillus thuringiensis.

Question. Bt-toxins are released as inactive crystals in the bacterial body. What happens to it in the cotton boll worm body that it kills the boll worm.
Answer : It is converted into an active protein (due to alkaline pH of the gut of the boll worm). The toxin binds to midgut cells / create pores / causes cell swelling and lysis that kills the bollworm.

Question. What is Gene therapy ?
Answer : Correction of genetic defect / involves delivery of a normal gene to take over the function of nonfunctional gene.

Short Answer Type Questions

Question. Why does the Bt toxin not kill the bacterium that produces it but kills the insect that ingests it ?
Answer : Exists as inactive protoxins. 
Becomes active in the gut of insect due to alkaline pH.
Detailed Answer :
Bt toxin does not kill the bacteria because when it is present in the bacteria, it is in an inactive and crystalline form. It becomes active and toxic when it is consumed by insects such as lepidopterans (armyworm), coleopterans (beetles) and dipterans (flies / mosquitoes) due to alkaline pH in their gut.

Question. What is gene therapy ? Name the first clinical case where it was used. 
Answer : (i) Collection of methods that allows correction of a gene defect that has been diagnosed in a child / embryo. 
(ii) Adenosine deaminase (ADA) deficiency. 
Detailed Answer :
Gene therapy is the method of inserting genes into an individual ‘s cell or tissue to cure various genetic disorders. It is used to replace a defective gene with a functional one. The first gene therapy method was used to cure the adenosine deaminase deficiency. 

Question. Write the function of adenosine deaminase enzyme. State the cause of ADA deficiency in humans. Mention a possible permanent cure for a ADA deficiency patient.
Answer : Adenosine deaminase enzyme is involved in purine metabolism. It is needed for the breakdown of adenosine from food. The disease is caused by a mutation in a gene on chromosome 20. The gene codes for the enzyme ADA. It is an inherited disorder that damages the immune system.
Treatment : (i) Bone marrow transplantation.
(ii) Transfusion of RBC.
If the gene isolated from bone marrow cells producing ADA is introduced in to cells at early embryonic stages, it could be a permanent cure.

Question. (i) Mention the cause and the body system affected by ADA deficiency in humans.
(ii) Name the vector used for transferring ADA-DNA into the recipient cells in humans. Name the recipient cells. 
Answer : (i) Defective gene not producing ADA, immune system is affected. 
(ii) A retroviral vector is used. Recipient cells are lymphocytes. 

Question. Explain the process of RNA interference.
Answer : This method involves silencing of a specific mRNA of the parasite due to complementary dsRNA molecule that binds to and prevents translation of the mRNA (silencing). The source of this complementary RNA could be from an infection from viruses having RNA genomes or mobile genetic elements (transposons) that replicate via RNA intermediate.

Question. How did Eli Lily synthesise the human insulin ? Mention one difference between this insulin and the one produced by the human pancreas. 
Answer : (i) In 1983, Eli Lily 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.
(ii) Chains A and B were produced separately, extracted and combined by creating disulphide bonds to form human insulin. 
Insulin produced by human pancreas has an additional C peptide. 

Question. Name the insect pest that is killed by the product of cry IAc gene. Explain how the gene makes the plant resistant to the insect pest.
Answer : Cotton bollworms
The protein coded by cryIAc gene control the cotton bollworms. CryIAc is responsible for producing a toxic crystalline protein known as cry protein (Bt toxin). It is non-toxic to the bacterium because it exist as an inactive protoxin.
When this toxin enters the insect, it get converted into active form due to the alkaline pH of the gut.
The activated toxin binds to the surface of the midgut epithelial cells and create pores and causes cell to swell, lyse and hence causing the death of the insect. 

Question. Why is functional insulin produced considered better than the ones used earlier by diabetic patient ?
Answer : The functional protein is produced by rDNA. It does not produce allergic reaction and complication while earlier insulin was produced or extracted from pancreas of cattle and pig. It caused allergy and many complication to the diabetic patients. 

Question. How has RNAi technique helped to prevent the infestation of roots in tobacco plants by a nematode Meloidegyne incognitia ?
Answer : RNAi technique is helpful in preventing the infestation of roots in tobacco plants. This can be done by introduction of nematode-specific genes using the Agrobacterium vectors 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 in the nematode. The consequence was that the parasite could not survive in transgenic host expressing specific interfering RNA. The transgenic plant therefore got itself protected from the parasite. 

Question. CrylAb is introduced in a plant to prevent infestation by corn borer.
(i) What is the resultant plant referred as ?
(ii) Summarize the action of the gene introduced ?
Answer : (i) Bt corn. 
(ii) Cry I Ab / Bt toxin gene codes for crystal protein, the Bt toxin protein exists as an inactive protein, but once an insect ingests it, it gets converted into an active form due to the alkaline pH of the gut which solubilizes the crystal. The activated toxin binds to the surface of mid gut and creates pores that cause swelling, lysis and eventually death of the insect. 

Question. What was the challenge for production of insulin using rDNA techniques ? How did Eli Lily produce insulin using rDNA technology ?
Answer : The challenge for production of insulin using rDNA technique was getting insulin assembled into a mature form. 
(i) Prepared two DNA sequence corresponding to A and B chains of human insulin.
(ii) Introduced them in plasmids of E. coli to produce insulin chains.
(iii) Chains A and B were produced separately.
(iv) Extracted and combined by creating disulfide bonds to form human insulin

Question. Why do lepidopterans die when they feed on Bt cotton plant ? Explain how does it happen.
Answer : Bt cotton contains inactive toxin protein / protoxin / insecticidal protein / crystal protein, once the insect ingest it, the inactive protoxins are converted into active form due to alkaline pH in gut, which solubilise the crystals, activated toxins binds to surface of midgut (epithelial cells), create pores, causes cell swelling, lysis eventually leading the death of the insect pest. 

Question. What is GMO? List any five possible advantages of a GMO to a farmer. 
OR
People are quite apprehensive to use GM crops.
Give three arguments in support of GM crops so as to convince the people in favour of such crops.
Answer : Plants / bacteria / fungi / animals whose genes have been altered by manipulation. 
Tolerance to abiotic stresses / like cold / drought / salt / heat, reduced reliance on chemical pesticides / pest resistant crops, reduce post harvest losses, increased efficiency of mineral usage by plants, enhanced nutritional value to create tailor made plant. 
Detailed Answer :
Genetically modified organisms are living organisms whose genes have been altered by biotechnological manipulation.
Advantages : 
(i) It makes crops more tolerant to abiotic stresses which can be in the form of cold, drought, salt or heat.
(ii) It reduces the reliance on chemical pesticides (pest-resistant crops).
(iii) It helps to reduce post harvest losses.
(iv) It increases the efficiency of mineral usage by plants. This prevents early exhaustion of fertility of soil.
(v) In enhances the nutritional value of food e.g. genetically modified variety of rice is rich in vitamin A. 

Question. How has the study of biotechnology helped in developing pest resistant cotton crop? Explain.
Answer : Some strains of Bacillus thuringiensis produce proteins that kill insects (pests), these crystals contain a toxic insecticidal protein, once the insect ingests this (inactive) toxin, it is converted into an active form, due to alkaline pH of the gut, activated toxin binds to surface of midgut epithelial cells and creates pores, causing swelling and lysis leading to death of pest. 

Question. Why is molecular diagnosis preferred over conventional methods ? Name any two techniques giving one use of each.
Answer : To allow early detection. 
Example : rDNA technology / PCR / ELISA / Probe
PCR-to detect low concentration of bacteria / virus (HIV).
ELISA–to detect antigen / to detect antibodies produce by those antigens / to detect HIV.
Probe-to detect a mutated gene from a normal one (any two corresponding functions).

Question. Mention the cause of ADA deficiency in humans.
How has genetic engineering helped patients suffering from it ?
Answer : Deletion / mutation of the gene which forms the enzyme – adenosine deaminase. 
Lymphocytes from the blood of the patient, can be grown in a culture outside the body, ADA cDNA gene can be inserted into the lymphocyte using retroviral vector, then lymphocytes can be returned to the patient. (They can start producing ADA).

Question. (i) Tobacco plants are damaged severely when infested with Meloidogyne incognita. Name and explain the strategy that is adopted to stop this infestation.
(ii) Name the vector used for introducing the nematode specific gene in tobacco plant.
Answer : (i) Nematode specific gene introduced into host plant (using Agrobacterium), produced dsRNA, RNAi initiated, specific mRNA of the nematode silenced and parasite dies. 
(ii) Agrobacterium tumefaciens. 

Question. How is the Bt cotton plant created as a GM plant ?
How is it protected against bollworm infestation ?
OR
(i) Why are certain cotton plants called Bt cotton plants ?
(ii) Explain how Bt cotton is resistant to pests.
Answer : (i) Certain cotton plants are called Bt cotton because specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into these cotton plants.
The proteins encoded by the genes cryIAc and cryIIAb control the cotton bollworms and that for cryIAb controls corn borer.
(ii) Specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into several crop plants such as cotton. The choice of genes depends upon the crop and the targeted pest, as most Bt toxin is insect-group specific. The toxin is coded by a gene named cry. There are a number of them, for example, the proteins encoded by the genes cryIAc and cryIIAb control the cotton boll worms, that of cryIAb controls corn borer. 

Question. How has the use of Agrobacterium as vectors helped in controlling Meloidogyne incognitia infestation in tobacco plants ? Explain in correct sequence.
OR
How did the process of RNAi interference help to control the nematode from infecting the roots of tobacco plants ? 
OR
How is a transgenic tobacco plant protected against Meloidogyne incognita ?
Answer : (a) Using Agrobacterium vector, nematode specific genes are introduced into host plant.
(b) Sense and antisense strands of mRNA are produced.
(c) ds RNA is formed.
(d) ds RNA initiates RNAi.
(e) Prevents translation of mRNA / Silencing of mRNA of parasite / nematode.
(f) Parasite will not survive. 

Question. How does Agrobacterium tumefaciens act as a suitable vector in the biotechnological experiments? Cite an example where it has been successfully used as a vector.
Answer : Agrobacterium tumefaciens (a pathogen of several dicot plants) is able to deliver a piece of DNA known as ‘T DNA’ to transform normal cells into tumor cells. The tumor inducing (Ti) plasmid of Agrobacterium (cloning vector) is no more used for pathogenic purposes, but the mechanism is used to deliver gene of interest, into plant where it multiplies.
Agrobacterium vector is used to transfer Nematode specific gene in the host plant (Tobacco) to develop Nematode resistant plant.

Long Answer Type Questions

Question. Explain the application of biotechnology in producing Bt cotton. 
Answer : Bt toxin gene has been cloned from the bacteria and has been expressed in plants, to provide resistance to insects (without the need for synthetic insecticide). Bt toxin gene forms protein crystals. These crystals contain a toxic insecticidal protein. Bt toxin protein exists as inactive protoxin in the host, but once the insect ingests the inactive toxin, it is converted into active form of toxin, due to alkaline pH of the gut which solubilises the crystals, causing death of the insect. 

Question. (i) Name the source from which insulin was extracted earlier. Why is this insulin no more in use by diabetic people ?
(ii) Explain the process of synthesis of insulin by Eli Lily company. Name the technique used by the company.
(iii) How is the insulin produced by human body different from the insulin produced by the abovementioned company ?
Answer : (i) Insulin from an animal source, though it caused some patients to develop allergy or other types of reactions to the foreign protein.
Insulin consists of two short polypeptide chains : chain A and chain B, which are linked together by disulphide bridges. In mammals, including humans, insulin is synthesized as a pro-hormone, which contains an extra stretch called the C-peptide.
(ii) In 1983, Eli Lily, 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 disulphide bonds to form human insulin.
(iii) The insulin produced by human body is different from the insulin produced by the above mentioned company. Insulin is synthesized as a prohormone (like a proenzyme, the prohormone 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.