Restriction endonucleases
Read the following passage carefully and answer the given question.
The cutting of DNA at specific locations became possible with the discovery of the so-called ‘molecular scissors’– (restriction enzymes). They cut DNA molecule at particular points by recognition a specific sequence of six base pairs. The 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. Each restriction endonuclease functions by ‘inspecting’ the length of a DNA sequence. Once it finds its specific recognition sequence, it will bind to the DNA and cut each of the two strands of the double helix at specific points in their sugar-phosphate backbones. Each restriction endonuclease recognizes a specific palindromic nucleotide sequences in the DNA. Palindromes are groups of letters that form the same words when read both forward and backward, e.g., “MALAYALAM”. As against a word-palindrome where the same word is read in both directions.
Restriction endonuclease enzyme used to cut:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → DNA
The passage says that restriction enzymes cut DNA at particular points by recognising a specific sequence of six base pairs. They belong to the nucleases, the enzymes that break nucleic acids. An endonuclease cuts inside the DNA, while an exonuclease removes nucleotides from the ends.
(1) RNA — Incorrect. RNA is removed by a different enzyme, ribonuclease.
(2) Protein — Incorrect. Proteins are broken down by proteases.
(3) Lipids — Incorrect. Lipids are broken down by lipases.
(4) DNA — Correct. A restriction endonuclease inspects the length of a DNA sequence. When it finds its specific recognition sequence, it binds to the DNA and cuts each of the two strands of the double helix.
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.