Q.Which chemical is utilised during the isolation of DNA at the end for the precipitation?
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The first practical steps of recombinant DNA technology are isolating pure genetic material from the source cell or tissue -- breaking open the cell wall with enzymes such as lysozyme, cellulase, or chitinase depending on the cell type, removing RNA and protein contaminants, and precipitating the purified DNA out of solution using chilled ethanol -- and then cutting that DNA at specific locations using an appropriate restriction enzyme through a process called restriction digestion. Because a genomic DNA sample usually contains many copies of a restriction enzyme's recognition sequence scattered throughout, digestion produces numerous fragments of different sizes; these are separated by size using agarose gel e …
After a cell is broken open and its RNA and protein removed, the remaining purified DNA still needs a final step to bring it out of aqueous solution as a visible, collectible form. …
In DNA isolation, after cell lysis and removal of proteins/RNA, chilled ethanol is added to the aqueous DNA solution to make the DNA precipitate out as visible fibrous strands.
The DNA isolation protocol involves breaking open cells (using lysozyme/cellulase/chitinase depending on the source), treating the extract with RNase and protease to remove RNA and proteins, and then adding chilled ethanol to the purified aqueous nucleic-acid solution. DNA, being insoluble in a cold alcohol environment, precipitates out and can be spooled out as fine white threads. Chilled metha …
- CBSE 2026Set ANNUAL1 markMCQQ.Which of the following enzymes is used to dissolve fungal cell wall ?(a) Lysozyme(b) Cellulose(c) Chitinase(d) Proteases
›Reveal solutionSolution
Chitinase digests chitin, the main structural polysaccharide of fungal cell walls, allowing release of the protoplast.
To obtain DNA/RNA or make a protoplast for genetic engineering, the cell wall must first be removed enzymatically. Bacterial cell walls are digested by lysozyme, plant cell walls by cellulase and pectinase, and fungal cell walls (made …
- CBSE 2025Set 57/5/11 markMCQQ.Isolation of DNA from a fungal cell can be achieved by using : (A) Cellulase (B) Chitinase (C) Lysozyme (D) Protease
›Reveal solutionSolution
To isolate DNA from a fungal cell, you need an enzyme that breaks down the tough, chitin-rich cell wall — and that enzyme is chitinase.
Fungal cells are fundamentally different from bacterial or plant cells in the composition of their cell wall. While bacteria have a peptidoglycan wall and plants have a cellulose wall, fungi possess a rigid structural layer made primarily of chitin — a long-chain polymer of N-acetylglucosamine. This chitinous wall is what gives fungi their strength and shape, but it also poses a significant barrier when you try to extract the DNA inside.
In molecular biology, the first step of DNA isolation is always cell lysis — breaking open the cell to release its contents. For a fungal cell, you cannot simply use a detergent or physical grinding alone; the chitin wall is too resilient. You need an enzyme that specifically targets and hydrolyses chitin. That enzyme is chitinase. Once chitinase weakens or digests the wall, the cell membrane becomes accessible, and you can proceed with standard lysis steps (using detergents like SDS and proteases to remove proteins, followed by precipitation of DNA). …
- CBSE 2025Set ANNUAL1 markQ.Fill in the blank: Genetic material RNA can be removed by treatment with ___. (Nucleases enzyme)
›Reveal solutionSolution
Treating a cell extract with the enzyme ribonuclease selectively degrades RNA while leaving DNA intact, useful during recombinant DNA/plasmid isolation.
During the isolation of genetic material for biotechnology (e.g., preparing pure DNA/plasmid), the extract typically contains other macromolecules like RNA and protein along with the desired DNA. RNA is specifically removed by treating the …
- CBSE 2024Set 57/2/11 markMCQQ.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.
›Reveal solutionSolution
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. …
- CBSE 2024Set E1 markMCQQ.For isolation of DNA a fungus is treated with which enzyme?(a) Lysozyme(b) Cellulase(c) DNase(d) Chitinase
›Reveal solutionSolution
DNA isolation needs the cell wall removed first; a fungal wall (chitin) is digested with chitinase.
To isolate DNA, the cell must first be opened by digesting its wall with an appropriate enzyme. The enzyme chosen depends on the cell wall's composition: lysozyme for bacteria (peptidoglycan), cellulase for plant cells (cellulose), and chitinase for fungi, whose …
- CBSE 2024Set ANNUAL1 markQ.In Recombinant DNA technology, precipitated DNA can be separated by ________.
›Reveal solutionSolution
After alcohol precipitation, DNA appears as fine threads; it is pelleted and separated from the rest of the solution by centrifugation.
In recombinant DNA technology, once cells/tissue are lysed with enzymes (lysozyme for bacteria, cellulase for plant cells, chitinase for fungi) to release DNA along with other macromolecules (RNA, proteins, polysaccharides, lipids), these contaminants are first removed by treatment with RNase, protease and other steps. The purified DNA is then made to precipitate out of the chilled solution by adding chilled ethanol, where it becomes visible as fine collapsed threads. To separate this precipitated DNA (and other biomolecules) from the rest of the solution, the mixture i …
- CBSE 2024Set ANNUAL1 markMCQQ.Match the organism's cell wall with the enzyme in which it is foundi) Bacteria a) Cellulaseii) Plant cells b) Chitinaseiii) Fungus c) Lysozyme(a) i(b), ii(a), iii(c)(b) i(c), ii(b), iii(a)(c) i(a), ii(c), iii(b)(d) i(c), ii(a), iii(b)
›Reveal solutionSolution
Lysozyme digests bacterial cell walls, cellulase digests plant cell walls, and chitinase digests fungal cell walls — all used to prepare protoplasts.
To isolate genetic material or produce protoplasts for genetic engineering, the cell wall of the host organism must first be removed using an appropriate wall-degrading enzyme, matched to the composition of that organism's cell wall:
- Bacteria — cell walls (made mainly of peptidoglycan) are digested using the enzyme lysozyme.
- Plant cells — cell walls (made of cellulose) are digested using the enzyme cellulase. …
- CBSE 2023Set ANNUAL1 markQ.By which enzyme bacterial cell is broken?
›Reveal solutionSolution
To isolate DNA/proteins from bacteria, the cell wall is broken using the enzyme lysozyme, which digests the peptidoglycan layer.
Before DNA can be extracted and manipulated in genetic engineering, the source cell must be broken open (lysed) to release its cellular contents.
- Bacterial cells are treated with lysozyme, an enzyme that specifically degrades the peptidoglycan (murein) layer of the bacterial cell wall, causing the cell to burst (lyse) and release its contents including DNA, RNA, and proteins. …
- CBSE 2019Set ANNUAL1 markMCQQ.The first step of genetic engineering is(a) isolation of protein(b) isolation of RNA(c) isolation of genetic material(d) isolation and purification of protein
›Reveal solutionSolution
Genetic engineering always begins with isolating the DNA/gene of interest from the organism that carries it.
The process of genetic engineering follows a defined sequence of steps: identification and isolation of the desired genetic material (DNA) carrying the gene of interest from the source organism; cutting this DNA and a chosen vector using restriction enzymes; joining (ligating) the gene of interest into the vector to form recombinant DNA; introducing this recombinant DNA into a suitable host cell (transformation); and finally selecting the transformed host cells and allowing them to express and multiply the desired gene product. Isolation …
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