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.
The cutting of DNA at specific locations is performed by:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Molecular scissors
Restriction enzymes are the molecular scissors. Each enzyme recognises a particular base sequence and cuts the DNA there.
(1) Molecular scissors — Correct. These are the restriction enzymes that cut DNA at specific sites.
(2) Vectors — Incorrect. A vector is a carrier, such as a plasmid, that delivers the alien DNA into the host. It does not cut DNA.
(3) DNA polymerase — Incorrect. This enzyme makes a new DNA strand on a template, as in replication and PCR. It does not cut DNA at specific sites.
(4) RNA polymerase — Incorrect. This enzyme makes RNA from a DNA template in transcription.
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:
Principles of Biotechnology – “… Stanley Cohen and Herbert Boyer accomplished this in 1972 by isolating the antibiotic resistance gene by cutting out a piece of DNA from a plasmid which was responsible for conferring antibiotic resistance. The cutting of DNA at specific locations became possible with the discovery of the so-called ‘molecular scissors’- restriction enzymes.”