Which enzymes are used to break open the following cells to release their DNA?
i) Bacteria
ii) Fungi
iii) Plant cells
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → i - Lysozyme, ii - Chitinase, iii - Cellulase
To isolate DNA, the cell must first be broken open. Each kind of cell is opened with an enzyme that digests the material of its outer covering. The bacterial cell is opened with lysozyme, the fungal cell with chitinase (its wall contains chitin), and the plant cell with cellulase (its wall is made of cellulose).
Option (1) i - Protease, ii - Cellulase, iii - Chitinase — Incorrect. Protease digests proteins. The book uses it later, to remove proteins from the released DNA, not to open bacteria. Cellulase and chitinase are also swapped: fungi need chitinase and plants need cellulase.
Option (2) i - Lysozyme, ii - Chitinase, iii - Cellulase — Correct. Every pair is right: lysozyme for bacteria, chitinase for fungi and cellulase for plant cells.
Option (3) i - Chitinase, ii - Lipase, iii - Cellulase — Incorrect. Chitinase does not open bacteria, which have no chitin wall. Lipase digests lipids (fats); it does not break the fungal wall. Only the plant pair is right.
Option (4) i - Lysozyme, ii - Cellulase, iii - Lipase — Incorrect. Lysozyme for bacteria is right, but cellulase does not suit fungi, and lipase cannot open plant cells, which need cellulase.
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. This can be achieved by treating the bacterial cells/plant or animal tissue with enzymes such as lysozyme (bacteria), cellulase (plant cells), chitinase (fungus). … The RNA can be removed by treatment with ribonuclease whereas proteins can be removed by treatment with protease.”