Read the following paragraph and answer the given questions.
Repeated amplification is achieved by the use of a thermostable DNA polymerase (isolated from a bacterium, Thermus aquaticus), which remain active during the high temperature induced denaturation of double stranded DNA. The separated DNA fragments can be visualised only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation. The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. The convention for naming these enzymes is the first letter of the name comes from the genus and the second two letters come from the species of the prokaryotic cell from which they were isolated, e.g., EcoRI comes from Escherichia coli RY 13. In EcoRI, the letter ‘R’ is derived from the name of strain. Roman numbers following the names indicate the order in which the enzymes were isolated from that strain of bacteria. 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. Since the DNA is enclosed within the membranes, we have to break the cell open to release DNA, RNA, protein, polysaccharides etc. The RNA can be removed by treatment with ribonuclease whereas proteins can be removed by treatment with protease. Other molecules can be removed by appropriate treatments and purified DNA ultimately precipitates out after the addition of chilled ethanol.
The convention for naming restriction enzymes is:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → First letter of the name from the genus and second two letters from the species of bacterium from which they were isolated
The passage gives the naming rule with an example: EcoRI comes from Escherichia coli RY 13. ‘E’ is the first letter of the genus Escherichia, ‘co’ the first two letters of the species coli, ‘R’ the strain RY 13, and the Roman number I shows it was the first enzyme isolated from that strain.
Option (1) First three letters of the name from the genus and second two letters from the species ... — Incorrect. Only one letter comes from the genus: the ‘E’ of Escherichia.
Option (2) First two letters of the name from the species and second two letters from the genus ... — Incorrect. It swaps genus and species and gives the wrong number of letters.
Option (3) First letter of the name from the species and second two letters from the genus ... — Incorrect. The letter counts are right but genus and species are reversed.
Option (4) First letter of the name from the genus and second two letters from the species ... — Correct. A restriction enzyme’s name has the first letter from the genus and the next two letters from the species of the prokaryote it was isolated from. So EcoRI comes from Escherichia coli RY 13: E from the genus, co from the species.
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.