Isolation of DNA
DNA பிரித்தெடுத்தல்
DNA is protected by complex cell walls, not just a plasma membrane. If you fail to choose the correct enzyme, you get zero yield. This is the fundamental barrier in all recombinant DNA technology.
The idea
Isolation begins by treating cells with specific enzymes: lysozyme for bacteria, cellulase for plant cells, and chitinase for fungi. This digestion releases DNA alongside RNA, proteins, and lipids. RNA is removed by ribonuclease and proteins by protease. Finally, chilled ethanol is added to precipitate the purified DNA as fine threads.
Why it matters
DNA must be isolated in a pure form, free from proteins, RNA, and lipids, to be accessible for restriction enzyme digestion.
NEET lens
NEET focuses on enzyme-organism matching. Memorize: Bacteria-Lysozyme, Plant-Cellulase, Fungi-Chitinase. Remember that chilled ethanol is the agent for precipitation, not just any alcohol.
Clinical significance
In diagnostic molecular biology, this process is the prerequisite for PCR-based detection of pathogens like Mycobacterium tuberculosis. If the DNA isolation is incomplete or contaminated with inhibitors, the PCR reaction fails, leading to false-negative clinical results.
Introduction
To cut DNA with restriction enzymes, it must first be obtained in pure form, free from other macromolecules.
Core concept
Steps (NCERT): since DNA is enclosed within membranes, cells are broken open using enzymes — lysozyme (bacteria), cellulase (plant cells), chitinase (fungus). Genes are located on long DNA molecules interwined with proteins such as histones. RNA is removed by treatment with ribonuclease, and proteins with protease. Other molecules can be removed by appropriate treatments, and purified DNA finally precipitates out after the addition of chilled ethanol. This can be seen as a collection of fine threads in the suspension. Once pure DNA is obtained, it is cut with restriction enzymes, and the cut DNA is checked by agarose gel electrophoresis.
Go deeper
Each enzyme matches the cell wall it must break: lysozyme for the bacterial cell wall, cellulase for plant cell walls (cellulose), chitinase for fungal walls (chitin).
From Class 10
To study DNA, scientists first break open cells and wash away everything else until only the DNA remains as white threads.