Principles and processes of biotechnology
Read the following passage carefully and answer the given questions.
The DNA fragments separate according to their size through sieving effect provided by the agarose gel. Vectors used at present, are engineered in such a way that they help easy linking of foreign DNA and selection of recombinants from non-recombinants. If we are able to link an alien piece of DNA with bacteriophage or plasmid DNA, we can multiply its numbers equal to the copy number of the plasmid or bacteriophage. In the year 1963, the two enzymes responsible for restricting the growth of bacteriophage in Escherichia coli were isolated. One of these added methyl groups to DNA, while the other cut DNA. The latter was called restriction endonuclease. The first restriction endonuclease - Hind II, whose functioning depended on a specific DNA nucleotide sequence was isolated and characterised five years later. In PCR reaction, multiple copies of the gene of interest are synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA). 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.
Which one of the following features is not present in cloning vector?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Micro-injection
A cloning vector carries an alien piece of DNA into a host and lets it multiply there. To do this it needs three features: an origin of replication, a selectable marker and cloning sites.
(1) Selectable markers — A feature of a cloning vector. A marker, such as a gene for antibiotic resistance, helps to identify the transformants and to remove the non-transformants.
(2) Micro-injection — Not a feature of a cloning vector. This is a method of putting recombinant DNA into a host: the DNA is injected directly into the nucleus of an animal cell. It is not a part of the vector.
(3) Origin of replication — A feature of a cloning vector. This is the sequence from where replication starts. Any DNA linked to it can multiply in the host, and it also controls the copy number.
(4) Cloning sites — A feature of a cloning vector. The vector needs very few, preferably single, recognition sites for the restriction enzymes, so that the alien DNA can be linked at one place.
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.”
Cloning Vectors – “… In a method known as micro-injection, recombinant DNA is directly injected into the nucleus of an animal cell.”