Which one of the following enzymes is known as “molecular scissors” in genetic engineering?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Restriction enzymes
Restriction enzymes cut DNA at specific places. Each one recognises a particular sequence of bases, so they are called molecular scissors. They are the first tool of recombinant DNA technology, because the gene of interest and the vector must both be cut before they can be joined.
(1) Restriction enzymes — Correct. They cut DNA at specific sites.
(2) Ligase — Incorrect. DNA ligase joins cut DNA ends. It is the “glue”, not the scissors.
(3) β-galactosidase — Incorrect. This enzyme is used to select recombinants. When a foreign gene is inserted into its gene, the enzyme is not made, and the colony stays colourless.
(4) DNA polymerase — Incorrect. It builds new DNA strands during replication and in PCR. It does not cut DNA.
Note: A similar question was also asked in CUET (UG) 2025 on 23-05-2025 (Slot 2), and in CUET (UG) 2023 on 11-06-2023 (Slot 3).
NCERT Extract:
Principles of Biotechnology – “… 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.”