Recombinant DNA
Read the following passage carefully and answer the given questions.
Recombinant DNA can be forced into competent cells by incubating the cells with recombinant DNA on ice, followed by heat shock and placing them back on ice. This enables the bacteria to take up the recombinant DNA. In a method known as micro-injection, recombinant DNA is directly injected into the nucleus of an animal cell. In another method, suitable for plants, cells are bombarded with high velocity micro-particles of gold or tungsten coated with DNA in a method known as gene gun and the last method uses ‘disarmed pathogen’ vectors, which when allowed to infect the cell, transfer the recombinant DNA into the host. 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. 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.
Bacterial cell is treated with ___________ to release the DNA.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Lysozyme
DNA is enclosed within the cell membranes, so the cell must be broken open to release it. For this the cells are treated with an enzyme that digests the cell wall. The enzyme depends on the kind of cell. Here the cell is a bacterial cell, so the enzyme is lysozyme, which breaks the bacterial cell wall.
(1) Cellulase — Incorrect. It digests cellulose, the main part of the plant cell wall. It is used for plant cells.
(2) Chitinase — Incorrect. It digests chitin, the main part of the fungal cell wall. It is used for fungus.
(3) Lysozyme — Correct. It is the enzyme used for bacterial cells.
(4) Pectinase — Incorrect. It digests pectin, which holds plant cells together. NCERT does not name it for releasing DNA from bacteria.
Note 1: 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.
Note 2: A similar question was also asked in CUET (UG) 2023 on 07-06-2023 (Slot 3).
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).”