BIOTECHNOLOGY : PRINCIPLES AND PROCESSES
Read the following passage carefully and answer the given questions.
The first constructed recombinant DNA emerged from the possibility of linking a gene encoding antibiotic resistance with a native autonomously replicating circular extra-chromosomal DNA of Salmonella typhimurium. Stanley Cohen and Herbert Boyer accomplished this 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’. 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 later was called restriction endonuclease. The cut piece of DNA was then linked with the plasmid DNA. These plasmid DNA act as vectors to transfer the piece of DNA attached to it.
Identify the enzyme which is useful for cutting DNA at specific locations.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Restriction enzyme
The passage says that cutting DNA at specific locations became possible with the discovery of the ‘molecular scissors’, the restriction enzymes. A restriction endonuclease recognises a specific base sequence in DNA and cuts both strands there.
(1) Restriction enzyme — Correct. It cuts DNA at specific sites.
(2) DNA ligase — Incorrect. DNA ligase does the opposite job. It joins cut pieces of DNA, such as the gene and the vector.
(3) DNA polymerase — Incorrect. DNA polymerase makes new DNA on a template, as in replication and PCR.
(4) RNA polymerase — Incorrect. RNA polymerase makes RNA from DNA during 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.