Page 16 - Biology - XII

Supernatant having DNA

add ice-cold
isopropanol
whitish fl oat
has DNA

Separation of supernatant liquid (aqueous layer) Isolated DNA

Fig. 3.1 (a): Isolation of DNA from frozen pea seeds

Fig. 3.1(b): DNA that separates out is removed by spooling

Conclusion
1. Isolation of DNA from plant tissue is complex because of two reasons:

(i) Presence of cell walls in plant tissue which needs to be broken to allow DNA to move out.
(ii) Presence of special cell inclusions in the cell sap/cytoplasm which must be removed before
getting to nucleus.
2. DNA isolation protocol (procedure) also separates other compounds—lipids, proteins, etc. present in
the cells.
3. DNA isolation protocol makes use of the fact that lipids and proteins are soluble in chloroform and
DNA is soluble in water/aqueous solutions.

Precautions
1. Frozen material must be used in case of plant parts. 3. Incubation for proper time must be done.
2. Buff er solution must be fresh. 4. Proper centrifugation gives better results.

VIVA VOCE

Q1. Why is chloroform: isoamyl alcohol used?
Ans. It is used to dissolve lipids and proteins present in cells.

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