How is DNA isolated in pure form from a cell? Describe the experiment to isolate DNA from a plant material.

How to lay out the answer. Follow the frame, then write it in your own words.

1 · State why purity matters. Restriction enzymes cut DNA properly only when it is free from other macromolecules.
2 · Break the cells. Use lysozyme for bacteria, cellulase for plant cells or chitinase for fungi.
3 · Remove other molecules.
- RNA by ribonuclease.
- Proteins by protease.
- Others by suitable treatments.
4 · Precipitate the DNA. Add chilled ethanol; DNA comes out as fine threads, collected by spooling.
5 · Describe the practical.
- Grind spinach with salt and detergent; filter.
- Add meat tenderiser (protease).
- Layer ice-cold ethanol; white DNA threads appear at the junction.
6 · Draw the set-up. [Diagram: test tube with filtrate below, ethanol layer above, white DNA threads at the junction, glass rod winding them]
7 · Link to real life. Forensic and hospital labs use the same principle for DNA fingerprinting and diagnosis.
8 · Close in one line. So pure DNA is the first step of every recombinant DNA experiment.

Scoring tip: Match each enzyme to its cell type, and use the word 'spooling'.