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.
Release of DNA along with other macromolecules such as RNA, proteins, polysaccharides and lipids can be achieved by treating the bacterial cells with enzyme:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Lysozyme
To use DNA in recombinant DNA technology, it must first be isolated in pure form. DNA is enclosed within membranes, so the cell must be broken open to release it. The enzyme used depends on what the cell wall is made of. Lysozyme breaks the bacterial cell wall, cellulase breaks the plant cell wall and chitinase breaks the fungal cell wall.
(1) Cellulase — Incorrect. It is used for plant cells, whose wall is made of cellulose.
(2) Lysozyme — Correct. It breaks open bacterial cells.
(3) Chitinase — Incorrect. It is used for fungi, whose wall contains chitin.
(4) Ligase — Incorrect. DNA ligase joins pieces of DNA. It does not break cells.
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:
Isolation of the Genetic Material (DNA) – “… Since the DNA is enclosed within the membranes, we have to break the cell open to release DNA along with other macromolecules such as RNA, proteins, polysaccharides and also lipids. This can be achieved by treating the bacterial cells/plant or animal tissue with enzymes such as lysozyme (bacteria), cellulase (plant cells), chitinase (fungus).”