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.
Which one of the following enzymes is the first restriction endonuclease?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Hind II
In 1963, two enzymes that restrict the growth of bacteriophages were isolated from E. coli. One added methyl groups to DNA and the other cut DNA, the restriction endonuclease. Five years later, the first restriction endonuclease whose action depended on a specific DNA sequence, Hind II, was isolated and studied. It always cuts DNA at a particular point, by recognising a specific sequence of six base pairs.
(1) EcoRI — Incorrect. EcoRI comes from Escherichia coli RY 13. It is widely used, but it was not the first.
(2) Hind II — Correct. It was the first restriction endonuclease.
(3) Hind III — Incorrect. Hind III is a different enzyme from the same bacterium, not the first one described.
(4) BamHI — Incorrect. BamHI is another restriction enzyme, found later.
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NCERT Extract:
Restriction Enzymes –
