Assertion (A): In order to cut the DNA with restriction enzymes, it needs to be in pure form, free from other macro-molecules.
Reason (R): The RNA can be removed by treatment with ribonuclease whereas proteins can be removed by treatment with protease.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both Assertion (A) and Reason (R) are correct but R is not the correct explanation of A.
Assertion (A): In order to cut the DNA with restriction enzymes, it needs to be in pure form, free from other macro-molecules. — True. A is about why DNA must be purified before it is cut. Restriction enzymes need clean DNA to act on.
Reason (R): The RNA can be removed by treatment with ribonuclease whereas proteins can be removed by treatment with protease. — True. R is about how two of the other macromolecules are removed. Ribonuclease digests RNA and protease digests proteins.
Why R does not explain A? A says that pure DNA is needed for restriction enzymes to cut it. R only gives the method used to remove RNA and proteins. Knowing which enzyme removes RNA does not tell us why the DNA has to be pure in the first place; R describes the step, not the reason for it. So both statements are correct, but R is not the explanation of A.
NCERT Extract:
Isolation of the Genetic Material (DNA) – “… In order to cut the DNA with restriction enzymes, it needs to be in pure form, free from other macro-molecules. 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. … 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.”