CBSE Questions for Class 12 Medical Biology Biotechnology: Principles And Processes Quiz 3 - MCQExams.com

• Plasmids are low molecular weight extrachromosomal DNA that carries the origin of replication, restriction sites, and selectable markers to confer readily selectable phenotypic traits on host cells. 
• Plasmid vector from B subtilis, pBP26, can clone the DNA segment of 10-15 kb.
• Bacteriophages have linear DNA that is cut to insert the gene of interest thereby generating chimeric DNA and used as a vector but has limitation on the size of cloned DNA as too large DNA segment cannot be accommodated into a small phage head.
• Agrobacterium tumefaciens have the capacity to transfer its Ti and Ri plasmids to host cells, which allow them to serve as vectors for large DNA segments up to 25 kb. The transformed cell is easily identified by the presence of tumors.
• The E coli phage contains an origin of replication, few essential genes, single-stranded protruding cohesive ends of 12 bases which allow it to anneal to form cos sites where a gene of interest is cloned. Size of eukaryotic genes are big enough which cannot be cloned into plasmids or phage vectors. 

1. Trichoderma harzianum is a bio fungicide and is used for suppression of various disease-causing fungal pathogens. Penicillium expansum, blue mold, causes postharvest decay of stored apples and produces the carcinogenic mycotoxin patulin.
2. Meloidogyne incognita, southern root-knot nematode" or the "cotton root-knot nematode", is a nematode with multiple hosts.
3. Agrobacterium tumefaciens is a soil-plant pathogenic bacterium that carries Ti plasmid. It can transfer a particular segment of the tumor-inducing (Ti) plasmid into the nucleus of infected cells.
4.  The transferred T-DNA is then integrated into the host genome and transcribed with it. 
5. This ability of Agrobacterium tumefaciens to transfer the T-DNA in host genome is explored in genetic engineering to transfer the desired DNA segment, carrying the gene of the interest, into genome of selected organisms. Option D is the correct answer. 

• PCR technique amplify the gene of interest in three steps namely denaturation of target DNA (thermal cycle to separate the DNA strands), annealing of primers to the ssDNA, and polymerization (extension of primer into complete DNA strand complementary to the template strand).
• After completion of one cycle of PCR, two copies of the target DNA are produced both of which serve as a template for the next PCR cycle and produce 4 copies. 
• Hence, there is an exponential amplification of DNA copies. 
• The total number of DNA molecules, produced after "n" PCR cycle = $$2^n$$. Thus, the total number of DNA molecules, produced after "6" PCR cycles = $$2^6$$ = 64. 

• Restriction endonucleases recognize specific sequences in the incoming DNA and digest the DNA into fragments. 
• They cut the DNA either at specific sites and are synthesized by bacteria as part of their defense mechanism. 
• The restriction sites are very short sequences and can be present in their own DNA. 
• Its own DNA is protected from destruction by adding methyl groups to it. 
• Only a few specific bases are modified on each strand.

• Agrobacterium tumefaciens is a soil-plant pathogenic bacterium that carries Ti plasmid. 
• It can transfer a particular segment of the tumor-inducing (Ti) plasmid into the nucleus of infected cells. 
• The transferred T-DNA is then integrated into the host genome and transcribed with it. 
• This ability to transfer the T-DNA in the host genome is explored in genetic engineering to transfer the desired DNA segment, carrying the gene of the interest, into the genome of selected organisms. 
• This exceptional ability to transfer part of the plasmid into the nucleus of infected cells is not found in any other bacteria, which makes Agrobacterium tumefaciens the best genetic vector in plants.

DNA polymerase enzyme synthesizes DNA strands by adding deoxyribonucleotides to 3' end of the primer via phosphodiester bonds; it uses parental DNA as a template. Kary Mullis got Nobel prize, in 1993 in chemistry, for the invention of polymerase chain reaction (PCR).  PCR - technique amplify the gene of interest.

• Fermentation is a metabolic process that converts sugar to acids, gases or alcohol anaerobically. It occurs in yeast and bacteria, but also in oxygen-starved muscle cells, as in the case of lactic acid fermentation.
  
  
• By fermentation, the yeast species Saccharomyces cerevisiae converts carbohydrates to carbon dioxide, acetic acid and alcohols like ethanol, butanol, phenethyl and amyl alcohol. 

• The bacteria (prokaryotes) contain special types of enzymes called the restriction enzymes.
•  These enzymes are responsible for cleaving the viral DNA that enters the bacterial cell for the infection, thereby restricting the growth of the virus particles. 
• Therefore, these are nucleases. 
• These do not degrade the DNA of the bacterial cell because the DNA is protected by methylation. 
• Due to their specific cleaving activity, the restriction enzymes are widely used in rDNA technology.

• Recombinant DNA technology includes techniques for the creation of recombinant DNA which carries DNA from two different sources. 
• It includes isolation of target DNA, cutting of DNA at precise locations using restriction endonucleases, selection of a small molecule of DNA that can self-replicate, called cloning vectors, insertion of DNA with the gene of interest in vector DNA to make recombinant DNAs, insertion of recombinant DNA to a host cell that will provide the enzymatic machinery for DNA replication and selection of host cells that contain recombinant DNA. 
• Thus, among the given options, EDTA is first used to drive the lysis of bacterial cells to isolate target DNA and vector molecule. 
• Then, restriction enzymes (IV) are used for cutting the desired DNA sequence followed by use of DNA ligase (II) enzyme to join the desired gene sequence with vector DNA and the recombinant DNA molecule is produced. 
• This is followed by the insertion of recombinant DNA into the host cell, for which calcium chloride (I) mediated gene transfer technique can be used.