Which of the following statements are correct regarding isolation of DNA?
A. DNA ultimately precipitates after the addition of chilled ethanol.
B. Separated DNA can be removed by autoradiography.
C. The RNA can be removed by treatment with ribonuclease.
D. DNA can be released from the cell along with other macromolecules by treating it with enzymes.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, C and D only
Isolating DNA involves three jobs: break the cell open, remove everything that is not DNA, and then bring the DNA out of the solution.
A. DNA ultimately precipitates after the addition of chilled ethanol. — Correct. DNA does not dissolve in chilled ethanol. It comes out of the solution as fine threads.
B. Separated DNA can be removed by autoradiography. — Incorrect. Autoradiography only detects molecules that carry a radioactive label. It does not remove anything. The DNA threads are lifted out by spooling, that is, by winding them on a glass rod.
C. The RNA can be removed by treatment with ribonuclease. — Correct. Ribonuclease is an enzyme that digests RNA. In the same way, protease is used to remove proteins.
D. DNA can be released from the cell along with other macromolecules by treating it with enzymes. — Correct. Lysozyme (for bacteria), cellulase (for plant cells) and chitinase (for fungi) break the cell wall. The DNA then comes out together with RNA, proteins, polysaccharides and lipids.
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). You know that genes are located on long molecules of DNA interwined with proteins such as histones. 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. This can be seen as collection of fine threads in the suspension (Figure 9.5).”
Figure 9.5 DNA that separates out can be removed by spooling