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.
Autonomously replicating circular extra-chromosomal DNA is known as:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Plasmid
The passage describes the “native autonomously replicating circular extra-chromosomal DNA” of Salmonella typhimurium. Such DNA is called a plasmid. A plasmid lies outside the chromosome of a bacterium and copies itself on its own. Because it can carry a joined piece of DNA with it, a plasmid is used as a vector in recombinant DNA technology.
(1) Bacteriophage — Incorrect. A bacteriophage is a virus that infects bacteria. It is not part of the bacterium’s own DNA.
(2) Plasmid — Correct. A plasmid is autonomously replicating, circular, extra-chromosomal DNA.
(3) Nucleolus — Incorrect. The nucleolus is a body inside the nucleus of eukaryotic cells, where ribosomal RNA is made.
(4) Nucleosome — Incorrect. A nucleosome is a unit of DNA packaging, DNA wrapped around histones.
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 – …
