BIOTECHNOLOGY : PRINCIPLES AND PROCESSES
Read the following passage carefully and answer the given questions.
Biotechnology deals with large scale production and marketing of products and processes using live organisms, cells or enzymes. Modern biotechnology using genetically modified organisms was made possible only when man learnt to alter the chemistry of DNA and construct recombinant DNA. This key process is called recombinant DNA technology or genetic engineering. This process involves the use of enzymes, viral vectors to carry the foreign DNA into host organisms, expression of the foreign gene, purification of the gene product, and finally making a suitable formulation for marketing. Restriction endonucleases are used in genetic engineering to form ‘recombinant’ molecules of DNA, which are composed of DNA from different sources/genomes. Gene cloning allows us to isolate and introduce only one or a set of desirable genes without introducing undesirable genes into the target organism. The ability to multiply copies of antibiotic resistance gene in E. coli was called cloning of antibiotic resistance gene in E. coli. In PCR, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase.
In recombinant DNA technology, which one of the followings is not a feature required to facilitate cloning into a vector?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Bioreactors
A vector is a DNA molecule, such as a plasmid, that carries a foreign gene into a host cell. To work as a vector it must have three features: an origin of replication, a selectable marker and cloning sites.
(1) Origin of replication (ori) — A feature required for cloning into a vector. It is the sequence from where replication starts. Any DNA linked to it can be copied inside the host cell, and it also controls the copy number.
(2) Cloning sites — A feature required for cloning into a vector. These are sites where a restriction enzyme cuts, so that the foreign DNA can be joined to the vector.
(3) Bioreactors — Not a feature required for cloning into a vector. A bioreactor is a large vessel in which cells are grown to make a product in large amounts. It is a piece of equipment, not part of the vector.
(4) Selectable markers — A feature required for cloning into a vector. A marker, such as an antibiotic resistance gene, helps to find the cells that took up the vector and to remove the cells that did not.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Cloning Vectors – “… The following are the features that are required to facilitate cloning into a vector. (i) Origin of replication (ori) : This is a sequence from where replication starts and any piece of DNA when linked to this sequence can be made to replicate within the host cells. This sequence is also responsible for controlling the copy number of the linked DNA. So, if one wants to recover many copies of the target DNA it should be cloned in a vector whose origin support high copy number. (ii) Selectable marker : In addition to ‘ori’, the vector requires a selectable marker, which helps in identifying and eliminating nontransformants and selectively permitting the growth of the transformants. Transformation is a procedure through which a piece of DNA is introduced in a host bacterium (you will study the process in subsequent section). Normally, the genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E. coli. The normal E. coli cells do not carry resistance against any of these antibiotics. (iii) Cloning sites: In order to link the alien DNA, the vector needs to have very few, preferably single, recognition sites for the commonly used restriction enzymes.”
Obtaining the Foreign Gene Product – “… To produce in large quantities, the development of bioreactors, where large volumes (100-1000 litres) of culture can be processed, was required.”