(7) How to extract DNA from plant cells - a simple experiment with strawberry fruit

This section is illustrated by the extraction of DNA from strawberries by a simple experiment.

Humans have 23 pairs of chromosomes (46 in total). The modern common strawberry has 8 pairs of each of the 7 chromosomes (56 in total) and is a rich 'school/college experiment' source of DNA.

 

1. You need an appropriate source e.g. split peas, strawberries, kiwi fruit, onions or bananas etc.

However, it is reported that the 'white strands' of DNA from fruit, may actually contain pectin too!

Any green leaves or stalk should be removed from the strawberry.

You can use a plastic bag or beaker in the first steps, you then need a test tube and filter funnel and filter paper.

 

2. The starting plant material is well mashed, but avoid creating air bubbles in the mash.

Squishing!

You can crush the strawberries in a plastic bag for a few minutes.

 

3. The mash is scraped into a beaker containing a solution of detergent and salt (the DNA extraction liquid).

You can add this mixture to the plastic bag or beaker of crushed strawberry.

With a plastic bag, its easier to do further effective crushing if you add the detergent/salt solution to the bag.

The detergent further helps to break down the cell membranes to release the DNA from the cell nuclei.

The salt makes the DNA strands stick together.

 

4. The resulting mixture is filtered into a test tube/2nd clean beaker. I used a hand held coffee filter paper!

Filtering!

In school/college you can use a normal filter funnel and filter paper, as in your chemistry lessons!

This removes the froth and the bigger insoluble bits of the plant cells.

Kitchen style!

The filtrate was transferred from the 2nd clean beaker into a test tube (if not already in a test tube).

 

5. Some ice-cooled alcohol is carefully added to the filtered mixture down the side of the test tube.

Adding alcohol, mixture goes cloudy

 

6. A band of white precipitated DNA strands should form - DNA is not soluble in cold alcohol.

White coagulated mass of DNA

 

7. You can then extract the DNA from this band with a glass rod.

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Key points for an experiment to extract DNA from plant material

Based on the syllabus-specifications for students taking the AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10).

DNA Extraction from Plant Cells

1. Aim of the Experiment

The purpose of this experiment is to extract DNA from plant cells using a simple method that breaks down the cell structure, removes proteins, and allows the DNA to be observed.

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2. Materials Needed

• Plant material (e.g., fresh spinach, strawberries, or bananas)

• Washing-up liquid (or mild detergent)

• Salt (table salt)

• Distilled water

• Ice-cold ethanol (or surgical spirit)

• Beaker

• Pestle and mortar (or blender)

• Fine sieve or coffee filter paper

• Test tubes

• Glass rod or wooden splint

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3. Step-by-Step Method

Step 1: Prepare the Plant Cells

• Chop the plant material into small pieces and place it into a pestle and mortar.

• Add a pinch of salt and a few drops of washing-up liquid.

• Grind the mixture while adding a small amount of distilled water until it forms a liquid extract.

• The detergent helps break down cell membranes, releasing the DNA.

Step 2: Filter the Solution

• Pour the mixture through filter paper (or a sieve) into a clean beaker.

• This removes solid debris, leaving behind the cell extract containing DNA.

Step 3: Precipitate the DNA

• Take 2-3 ml of the filtered extract into a test tube.

• Carefully pour ice-cold ethanol down the side of the tube to form a separate layer above the extract.

• Do not mix the layers—DNA will precipitate at the boundary between the ethanol and the cell extract.

Step 4: Observe and Collect the DNA

• After a few minutes, white, stringy DNA will start to appear in the ethanol layer.

• Use a glass rod or wooden splint to gently lift the DNA strands.

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4. Explanation of the Process

• Cell Breakdown: The washing-up liquid breaks open the cell membranes and nuclear envelope to release DNA.

• Protein Removal: Salt helps to remove proteins that can tangle DNA molecules.

• DNA Precipitation: Ethanol makes DNA insoluble, causing it to clump together and become visible.

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5. Importance of DNA Extraction in Biology

• Allows scientists to study DNA structure and function.

• Used in genetic research, crime investigations (DNA fingerprinting), and medical diagnostics.

• Essential for techniques like genetic engineering and cloning.

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6. Other points

• Always explain the role of each ingredient (detergent, salt, ethanol).

• Use clear diagrams to illustrate DNA precipitation.

• Link the process to real-world applications in genetics and biotechnology.

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Summary of learning objectives and key words or phrases

Understand the details of an experiment to extract DNA from plant cells e.g. strawberries, describe the procedure, the chemicals needed e.g. alcohol, detergent, salt and crushed strawberries.

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