Biology · Biotechnology: Principles and Processes · NEET
Isolation of genetic material means getting pure DNA out of a cell before we can cut it. First we break the cell open using enzymes (lysozyme for bacteria, cellulase for plant cells, chitinase for fungi). Then we remove RNA with ribonuclease and protein with protease, and finally the pure DNA precipitates out as fine white threads when we add chilled ethanol. Memory hook: "Break -> Remove -> Precipitate" (B-R-P).
DNA extraction in three steps: break the cell (lysozyme/cellulase/chitinase), remove RNA (RNase) and protein (protease), then precipitate pure DNA with chilled ethanol as fine threads.
Your doubts, answered
Why must DNA be isolated in pure form before it can be cut?
Restriction enzymes (molecular scissors) can only cut clean DNA. Inside a cell, DNA is mixed with RNA, proteins, polysaccharides and lipids. NCERT says the DNA must be "in pure form, free from other macro-molecules" so the enzyme can find and cut the exact site. So isolation always comes first in recombinant DNA technology.
Which enzyme breaks the cell open, and how do I remember them?
The cell wall is digested by an enzyme matched to the organism: lysozyme for bacteria, cellulase for plant cells, and chitinase for fungi. Easy match: bacteria have peptidoglycan (lyso-zyme), plant cell walls have cellulose (cellul-ase), fungal walls have chitin (chitin-ase). These enzymes break the cell; they do NOT cut the DNA.
How is RNA removed, and how is protein removed?
RNA is removed by ribonuclease (RNase) and protein (like the histones wrapped around DNA) is removed by protease. Remember the pairing: RNase removes RNA, protease removes protein. If you swap them (RNase for protein), it is wrong.
Why chilled ethanol and not room-temperature methanol or isopropanol?
NCERT names one specific reagent: chilled ethanol. DNA is not soluble in ethanol, so adding chilled ethanol makes purified DNA come out of solution (precipitate) as fine threads you can see. NEET options like isopropanol, methanol at room temperature, or chilled chloroform are traps; the NCERT answer is chilled ethanol.
What is the correct order of the whole process?
Break the cell open (with lysozyme/cellulase/chitinase) -> remove RNA (RNase) and protein (protease) -> add chilled ethanol -> DNA precipitates as fine threads. Only after this pure DNA is ready do we cut it with restriction enzymes.
⚠️ The NEET trap ✗ Students pick lysozyme (or any of these enzymes) as the reagent that cuts DNA at specific sites. ✓ Lysozyme, cellulase and chitinase only break open the cell wall to release DNA. Cutting DNA at specific sites is done later by restriction enzymes (endonucleases). And precipitation is done by chilled ethanol, not by these enzymes. 🧠 Break-open enzymes (lyso/cellul/chitin) OPEN the cell; restriction enzymes CUT the DNA. Different jobs, different step.
Real NEET questions
NEET 2019
DNA precipitation out of a mixture of biomolecules can be achieved by treatment with
A · Isopropanol
B · Chilled ethanol ✓
C · Methanol at room temperature
D · Chilled chloroform
Solution: After the cell is broken open and RNA/proteins are removed (by ribonuclease and protease), the purified DNA precipitates out on adding chilled ethanol, seen as fine threads. NCERT states "purified DNA ultimately precipitates out after the addition of chilled ethanol."
NEET 2021 / NEET 2023 Phase 1
During the purification process for recombinant DNA technology, addition of chilled ethanol precipitates out
A · RNA
B · DNA ✓
C · Histones
D · Polysaccharides
Solution: RNA is already removed by ribonuclease, protein/histones by protease, and other molecules by appropriate treatment. So chilled ethanol precipitates the purified DNA, not RNA, histones or polysaccharides. This is a direct NCERT statement.
NEET 2026
Assertion A: In recombinant DNA technology, lysozyme is used for disrupting bacterial cells while cellulase is used for plant cells. Reason R: Isolation of genetic material needs disruption of cells. Choose the most appropriate answer:
A · Both A and R are correct and R is the correct explanation of A ✓
B · Both A and R are correct but R is not the correct explanation of A
C · A is correct but R is not correct
D · A is not correct but R is correct
Solution: To isolate DNA the cell must be broken open. Cell walls are digested by enzymes specific to the organism: lysozyme (bacteria), cellulase (plant cells), chitinase (fungi). This is done precisely because genetic material is enclosed inside cells, so R correctly explains A.
Solved Biotechnology: Principles and Processes NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
