Read the following paragraph carefully and answer the given questions.
In the year 1963 the two enzymes responsible for restricting the growth of bacteriophage in E. coli were isolated. The first restriction endonuclease - Hind II, whose functioning depended on a specific DNA nucleotide sequence was characterized five years later. It was found that Hind II always cut DNA molecules at a particular point by recognizing a specific sequence of six base pairs. This specific base sequence is known as the recognition sequence for Hind II. Besides Hind II, today we know more than 900 restriction enzymes that have been isolated from over 230 strains of bacteria, each of which recognize different recognition sequences.
Restriction enzymes are also known as
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Molecular scissors
Option (1) Polymerase enzyme — Incorrect. A polymerase builds a chain of nucleotides. DNA polymerase, for example, makes a new DNA strand on a template. It joins nucleotides together; it does not cut DNA.
Option (2) Molecular scissors — Correct. A restriction enzyme cuts DNA at a specific place, at its own recognition sequence. It works like a pair of scissors that cuts a sheet only where we want. This cutting made it possible to take a gene out of one DNA and join it to another.
Option (3) Replicatory enzyme — Incorrect. Replication is the copying of DNA before a cell divides. The enzymes of replication make a copy of the whole DNA, with DNA polymerase as the main enzyme. Restriction enzymes do not copy DNA.
Option (4) Transcriptive enzyme — Incorrect. Transcription is the copying of one strand of DNA into RNA. Its enzyme is RNA polymerase, which makes RNA. It does not cut DNA.
Note: This passage is taken from NCERT as it is. 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 – “… The construction of the first recombinant DNA emerged from the possibility of linking a gene encoding antibiotic resistance with a native plasmid (autonomously replicating circular extra-chromosomal DNA) of Salmonella typhimurium. 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.”