Test: Processes of Recombinant DNA Technology (NCERT) - NEET MCQ

Stirred-tank bioreactor is used for processing large volumes of culture. It is a cylindrical tank with a curved base to facilitate the mixing of the reactor contents. The stirrer facilitates even mixing and oxygen availability throughout the bioreactor.

Recombinant DNA Technology Steps:
The correct sequence of steps in recombinant DNA technology is as follows:
(i) Isolation of the DNA fragments or genes to be cloned:
- This step involves extracting the specific DNA fragments or genes from a source organism.
(v) Insertion of the isolated gene in a suitable plasmid vector:
- The isolated gene is inserted into a plasmid vector, which acts as a carrier for the gene.
(ii) Introduction of the recombinant DNA into a suitable cell (usually E.coli) called host (transformation):
- The recombinant DNA is introduced into a host cell, typically E.coli, through a process called transformation.
(iv) Selection of the transformed host cells, and identification of the clone containing the desired gene/DNA fragment:
- The transformed host cells are selected and screened to identify the clone that contains the desired gene or DNA fragment.
(iii) Multiplication/expression of the introduced gene in the host:
- The introduced gene in the host cell undergoes multiplication and expression, resulting in the production of the desired protein or molecule.
Therefore, the correct sequence of steps in recombinant DNA technology is (i), (v), (ii), (iv), (iii), which corresponds to option C.

The correct option is C 4 and 7
The cost of gene cloning is far more than PCR because gene cloning requires many intricate steps. PCR takes less than 4 hours while gene cloning can take days.

Primers are small, chemically synthesised oligonucleotides that are complementary to the sequences, present at 3' end of the template DNA. They hybridise to the target DNA region, one to each strand of the double helix. These primers are oriented with their ends facing each other allowing synthesis of the DNA towards one another.

The final step of PCR is extension, wherein TaqDNA polymerase (isolated from a thermophilic bacterium Thermus aquaticus) synthesies the DNA region between the primers, using DNTPs (denoxynucleoside triphosphates) and Mg2⁺. The primers are extened towards each other so that the DNA segment lying between the two primers is copied. The optimum temperature for this polymerisation step is 72^∘C. Taq polymerase remains active during high temperature induced denaturation of double stranded DNA.

In addition to Tag DNA polymerase, Pfu polymerase and Tli polymerase have been isolated which are also thermostable. Pfu polymerase is isolated from Pyrococcus furiosus. Tli (vent) polymerase is isolated from Thermococcus litoralis.

After the formation of the product in bioreactors, it undergoes through some processes before a finished product is ready for marketing. The processes include separation and purification of products which is collectively called as downstream processing.

The purified DNA, after treatment with various enzymes, precipitates out after the addition of chilled ethanol. 
This is viewed as a collection of fine threads in the suspension and is easily collected. The process is known as DNA spooling.

Steps to transfer a desirable gene of interest into a plant:

• Isolation of desirable gene using restriction endonucleases and gel electrophoresis.
• Joining of desirable gene to a suitable cloning vector using ligases to create a recombinant DNA molecule.
• Transferring the recombinant DNA molecules to the target cells.
• Screening of cells. 
• Transformation.
• Selection of transformed cells.
• Regeneration of plants from the transformed cells to get transgenic plants. 

Eukaryotic genes do not function properly When transferred into bacterial cell because introns are present eukaryotic cells but are absent in prokaryotic cells. Hence, when bacterial cell is transformed with recombinant DNA is genrated human gene, it could not process it. As a result no desired protien will be produced.

Antibiotic resistance genes are selectable markers. Desirable genes are the ones which are introduced in the vector for getting desired protein product. In agarose gel electrophoresis, DNA fragments are separated according to their charge and size. After the formation of the product in a bioreactors, it undergoes through some processes before a finished product is ready for marketing. The processes include separation and purification of products which are collectively called as downstream processing.

The most commonly used bioreactors are of stirring type. Stirring type bioreactors are simple stirred-tank bioreactor and sparged stirred-tank bioreactor. 

In 1997, Rosie, the tirst transgenic cow was engineered to produce milk enriched with a human protein called alpha-lactalbumin, making it nutritionally more balanced. Restriction enzymes are used to cut DNA at specific sites.

Yeasts have been extensively used for functional expression of eukaryotic genes because they offer several advantages. Yeasts are the simplest eukaryotic organisms and like bacteria are single-celled, genetically well-characterised, easy to grow and manipulate. Since yeast is a eukaryote, it have an intron excision mechanism. Thus, it can be used for producing and expressing recombinant DNA of eukaryotes.