Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.
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Assertion : In a genetic engineering process, it is necessary to prepare sterile ambience.
Reason : Sterile ambience inhibits the growth of undesirable microbes during manufacture of product.
(a) : During sterilisation, the equipments are made free of any microorganisms before the addition of desired microbe or cell. Now, this desired organism does not get any competition from other organisms and expresses all its characters and grows effectively. Hence, sterilisation enables growth of only the desired microbe.
Assertion : Asexual reproduction is more important with regard to biotechnology.
Reason : Asexual reproduction preserves the genetic information while sexual reproduction permits variations.
(a) : Biotechnology studies need a quick growing population of genetically uniform individuals so that similar changes may be produced in all the genetically engineered organisms. Hence, asexual reproduction, which is a quicker and faster method of reproduction and preserves the genetic information of individuals, is better suited for biotechnological experiments.
Assertion: Genetic engineering can overcome the drawbacks of traditional hybridisation.
Reason : Genetic engineering can create desired DNA sequences to meet specific requirements.
(a) : Traditional hybridisation procedures involve mating of organisms to be modified with another individual of the same species having desired characters and screening the progeny for expression of desired set of characters. These procedures, very often lead to inclusion and multiplication of undesirable genes alongwith desired genes. Besides inter-specific hybridisation are generally not very successful. Genetic engineering can overcome all these drawbacks because use of recombinant DNA technology, gene cloning and gene transfer allow us to isolate and introduce only one or a set of desirable genes without introducing undesirable genes into the target organism that too from any distant organism.
Assertion : A piece of DNA inserted into an alien organism generally does not replicate if not inserted into a chromosome.
Reason : Chromosomes have specific sequences called ‘ori’ region where DNA replication is initiated.
(a) : ‘Origin of replication’ is a sequence from where replication starts by binding of polymerase enzyme. An isolated piece of DNA without origin of replication or ‘ori’ site cannot replicate and is gradually lost during nuclear divisions. But if it is inserted within a chromosome it is replicated along with the chromosome.
Assertion: Genetic engineering requires both nucleases and ligases.
Reason : Ligases produce the nick in the recombinant DNA molecule.
(c) : Nucleases are the enzymes that remove nucleotides or produce nick in the DNA strand. Ligases are called molecular glue as they join together two DNA strands by forming phosphodiester bonds between adjacent nucleotides.
Assertion : Restriction enzymes Hin and Hae are produced from two different genera of bacteria.
Reason: Hin is produced from Haemophilus influenzae while Hae is produced from Haemophilus aegyptius.
(d) : Hin and Hae, both are produced from a single genus Haemophilus but from two different species, i.e., H. influenzae and \(H\). aegyptius respectively.
Assertion : Restriction enzymes recognise palindromic sequences.
Reason : Palindromic sequences read same in both directions of the two strands.
(b)
Assertion : The matrix used in gel electrophoresis should have controllable pore size.
Reason : Agarose concentration can be changed to change pore sizes.
(b)
Assertion : All expression vectors are cloning vectors and vice versa.
Reason : Expression vectors need regulatory machinery suitable for the host.
(d) : All vectors used for propagation of DNA inserts in a suitable host are called cloning vectors. But when a vector is designed for the expression, i.e., production of the protein specified by the DNA insert, it is termed as expression vector. Expression vectors need regulatory machinery suitable for the host.
Assertion : E.coli having PBR322 with DNA insert at BamH I site cannot grow in medium containing tetracycline.
Reason : Recognition site for BamH I is present in tet \({ }^R\) region of \(p B R 322\).
(a) : pBR322 has recognition sites for several commonly used restriction enzymes. Recognition site for BamH I is present in tet \({ }^R\) region, i.e., region responsible for tetracycline resistance. When an insert is added at the BamH I recognition site the gene for tetracycline resistance becomes non-functional and the recombinant bacteria with plasmid pBR322 that has DNA insert at BamH I lose tetracycline resistance.
Assertion : A bacterial cell with no restriction enzymes will be easily infected and lysed by bacteriophages.
Reason : Restriction enzymes catalyse synthesis of protective coat around bacterial cell that prevents bacteriophage attack.
(c) : Restriction enzymes produced in a bacterial cell, recognise and cleave foreign DNA introduced (such as from bacteriophage) into the cell. Thus, bacterial cell cannot be infected and lysed by bacteriophage and hence a bacterial cell lacking restriction enzymes is easily susceptible to infection of phages. The DNA of the host bacterial cell is protected from its own restriction endonucleases by methylation (usually of \(A\) and \(C\) ) within their recognition sites.
Assertion: Special methods are used for transformation i.e., incorporation of recombinant DNA into host.
Reason : DNA is a hydrophilic molecule.
(a) : Transformation is permanent heritable change in a cell, particularly a bacterial cell, that occurs as a result of its acquiring foreign DNA. But cells normally do not take up foreign DNA molecule because DNA is a hydrophilic macromolecule and its movement through lipid membrane is opposed. Special methods such as \(\mathrm{CaCl}_2\) treatment, electroporation, particle delivery method, etc., are used to make host cells competent, i.e., able to take up foreign DNA.
Assertion: Use of chitinase enzyme is necessary for isolation of DNA from yeast cells but not in case of Spirogyra.
Reason: Fungal cell wall is made up of fungal cellulose or chitin.
(a) : Release of DNA from a cell is achieved by treating the cells or tissues with enzymes such as lysozyme (bacteria), cellulose (plant cells), chitinase (fungus), etc. These enzymes degrade cell wall; plasma membrane degrading enzymes like lipase, etc., are also needed. Since yeast is a fungus and fungal cell wall is made of chitin (fungal cellulose), isolation of DNA necessarily requires use of enzyme chitinase.
Assertion : PCR primers must not have self complementary regions.
Reason : Self complementary regions result in hairpin structures adversely affecting the PCR.
(a) : Primers are nucleotide sequences that serve as base for formation of new DNA strand. In PCR, primers are added on the ends of DNA strand to be copied and the primers are extended towards each other so that the DNA segment lying between the two primers is copied. If self complementary bases are present in primers then hydrogen bonds are formed between them and hairpin-like structure is formed. It makes the primers unsuitable for extension of strands in PCR.
Assertion : Downstream processing is generally considered more difficult and costlier in plants than that in microbes.
Reason : The process includes separation and purification of the product.
(b)
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