This Class 12 Biology practical focuses on the isolation of DNA from easily available plant materials such as spinach leaves, green pea seeds, papaya, or banana. The activity helps students understand the basic structure and extraction process of deoxyribonucleic acid (DNA), the genetic material responsible for inheritance.

In this practical, plant tissues are first crushed and mixed with a detergent solution to break cell membranes. Salt is added to separate proteins, and the mixture is filtered. Cold alcohol, usually chilled ethanol, is then gently poured, causing DNA to precipitate as white, thread-like strands. Students can observe this DNA using a glass rod or toothpick.

This experiment is simple, safe, and highly effective for demonstrating molecular biology concepts. It strengthens understanding of DNA structure, nucleic acids, and genetic material. This practical is important for CBSE Class 12 exams and enhances practical record writing and viva preparation.

AIM :- Isolate DNA from available plant material such as spinach, green pea seeds, papaya, banana etc.

REQUIREMENTS

Plant material (such as spinach leaves, green pea seeds or green papaya), mortar and pestle, beakers, test tubes, liquid detergent, non-iodised sodium chloride, distilled water, meat tenderizer or papain solution/juice of papaya/pine apple juice, 95% ethanol, spool etc.

PREPARATION OF SOLUTIONS

1. Detergent salt solution is prepared by adding 10 ml liquid detergent and 10 g of non-iodised sodium chloride to 90 mL of distilled water.

2. Meat tenderizer solution is prepared by adding 5g of tenderizer to 95ml of distilled water.

3. 5% NaCI solution is prepared by dissolving 5 g of non-iodised sodium chloride in 100 ml of distilled water.

4. Chilling of ethanol must be done by keeping 95%, ethanol in plastic bottle in the freezer over night.

PROCEDURE

1. Take 5g of the Plant tissue (spinach leaf/green pea seed/green papaya) and grind it in the mortar by adding 10 ml detergent, salt solution and filter it through muslin cloth.

2. Take 10 ml of the filtrate, add 3-4 ml tenderizer/papaya juice and swirl the test tube by holding the tube between the two hands to mix the contents.

3. Pour 10 mL chilled ethanol carefully down the side of test tube to form a layer on the top of the content; let it stand undisturbed for about 3 minutes.

4. Using the glass rod stir gently through interface of the two layers to collect the precipitate of DNA and place it in a test tube with 5% NaCl or distilled water.

The quantity of DNA present in the given plant material can be estimated through spectrophotometer.

OBSERVATION

The addition of ethanol to the solution causes DNA to precipitation. The DNA fibres appears as white precipitate of very fine threads on the glass spool.

PRECAUTIONS

1. The plant material should be washed thoroughly with distilled water to remove any dust and dried by blotting before weighing

2. All the glass wares used must be thoroughly cleaned and dried,

3. The chemicals and enzymes used for the experiment must be of standard quality which should be manufactured by standard pharmaceuticals.