Title:
DNA Extraction from Animal and Plant Tissues
Aim:
Students will follow the experiment and extract DNA from the cells of liver and from
the cells of onions
Class:
Transition year pupils
Equipment needed:

Raw liver

Onion

Knife

Distilled water

Sodium chloride

Sodium bicarbonate

Liquid detergent

3M sodium acetate

Ethanol

Balance

Ice water bath

Blender

Flasks, beakers, graduated cylinders and test tubes
Safety aspect:
General lab safety rules apply. No eating or drinking of the chemicals is allowed and
students must wear safety goggles and gloves during the experiment as contact with
some of the chemicals can be harmful. If any of the chemicals come in contact with a
person rinse with cold water.
Procedure:
1) Solution Preparation:

Chill a flask containing 50ml of ethanol in an ice-water bath

Prepare a buffer by dissolving 0.75g NaCl, 2.5g NaHCO3 and 1ml of
liquid detergent in 60ml.

Chill the solution in an ice-water bath. Obtain 1ml of aqueous 3M
sodium acetate solution
2) Extraction of DNA from liver:

Place 5cm liver and 30ml distilled water in blender. Blend for 30secs

Pour mixture and equal volume chilled buffer solution into small
beaker and stir for 2mins

Transfer 15ml of mixture to test tube and centrifuge for 3mins

If no centrifuge available shake vigorously. DNA will rise to top of test
tube
3) Precipitation of DNA:

Place 5ml of mixture into test tube

Carefully pour 10ml of ice cold ethanol down the side of test tube so
that two layers form

DNA will appear at the middle of these two layers. If long polymer
fibres are obtained they can be extracted using a fork
4) Extraction of DNA from onions:

Diagram:
Repeat procedure substituting onion for the liver.
This is a diagram of the DNA between two layers in a beaker. The DNA is the white
layer in between the purple and green layers.
In the second diagram the DNA can be seen as the white coloured material on top of
the red solution
This is a diagram showing the double strand helix of DNA
Results:
The result should be a piece of DNA extracted from both liver and onion cells
Conclusions:
It’s shown in this experiment that it is possible to extract DNA from onions and liver.
This is a useful experiment to conduct in the lab as it will get pupils interested in the
topic. This topic is on the junior science syllabus and will need to be covered and I
think this simple experiment should be done when pupils are studying this section.
The experiment is very simple and there is not too much needed to conduct it. The
pupils could bring the onion and liver and all the lab would have to supply is a few
chemicals so it’s a cost effective experiment
Questions:

Would you expect the same results from different cellular materials? Does
your experimental results conform your predictions?

Would you expect the same results for different amounts of blending?

DNA molecules can be very long, but their width is only a relatively small
number of atoms. Can you see a single molecule of DNA?
Links to Curriculum:
This section is linked into the junior science curriculum and will need to be covered
so therefore I found it to be a relevant and worthwhile learning experience. It can also
be introduced for transition year science/chemistry/biology. I feel interesting
practicals like these will help to ignite pupils interest in science subjects and will help
to increase the numbers taking these subjects as we all know that numbers are on the
decrease. Transition year pupils should be targeted for these kinds of experiments and
demonstrations as they will be the ones deciding what subjects to take at senior cycle.