Q.Assertion (A) : Specific enzymes are used to degrade the cell wall in organisms to isolate the DNA from the cell. Reason (R) : Fungal cell wall is degraded by the enzyme cellulase. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.
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Start your 14-day free trial to unlock the full solution →The assertion about using specific enzymes to degrade cell walls for DNA isolation is true, but the reason is false because fungal cell walls are degraded by chitinase (not cellulase, which acts on plant cellulose). The correct option is (C).
DNA isolation from cells requires breaking through the cell wall when present, and different organisms have different cell wall compositions that demand specific enzymatic approaches. The assertion recognizes this fundamental principle of molecular biology protocols.
The key insight here is matching the enzyme to the cell wall polymer. Cell walls are not universal structures—their chemical makeup varies dramatically across kingdoms, and each polymer requires its own hydrolytic enzyme.
Evaluating the Assertion
The assertion states that specific enzymes degrade cell walls to isolate DNA. This is absolutely correct. During DNA extraction protocols:
- Plant cells have cell walls made of cellulose, requiring cellulase
- Bacterial cells have peptidoglycan walls, requiring lysozyme
- Fungal cells have chitin-rich walls, requiring chitinase
Without enzymatic degradation of these barriers, you cannot efficiently lyse the cells and release the DNA. The specificity is crucial—using the wrong enzyme simply won't work because each targets different glycosidic bonds.
Evaluating the Reason
The reason claims that fungal cell walls are degraded by cellulase. This is false.
Fungal cell walls are primarily composed of chitin, a polymer of N-acetylglucosamine units linked by β-1,4-glycosidic bonds. Chitin is the same tough polysaccharide found in insect exoskeletons and crustacean shells.
Cellulase, on the other hand, hydrolyzes cellulose—a polymer of glucose units found in plant cell walls. The enzyme active site is shaped to recognize and cleave the β-1,4-glycosidic bonds between glucose residues, not N-acetylglucosamine. …
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