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.
Biolistics method is suitable for introduction of DNA into:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Plant cell
The biolistics or gene gun method fires tiny particles of gold or tungsten, coated with DNA, at high speed into the cells. It is the method used for plant cells.
(1) Animal cell — Incorrect. DNA is put into an animal cell by micro-injection, a direct injection into the nucleus.
(2) Bacterial cell — Incorrect. Bacterial cells are made competent with calcium. Then recombinant DNA is forced in by a heat shock.
(3) Fungal cell — Incorrect. NCERT names only plant cells for this method.
(4) Plant cell — Correct. It is the method that suits plants.
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:
Cloning Vectors – “… Recombinant DNA can then be forced into such cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 420C (heat shock), and then putting them back on ice. This enables the bacteria to take up the recombinant DNA. This is not the only way to introduce alien DNA into host cells. 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 biolistics or gene gun.”