Background

DNA is found in the CELLS of all plants and animals.

Cells are the “building blocks” that make up plants and animals – a bit like using Lego blocks to build an awesome model. DNA is the ‘code’ that tells those cells how to grow and what characteristics a living creature will have. It’s a bit like the instructions that come with a pack of Lego!

If you have a microscope you can see a cell and it might look like this;

Image modified from Clker-Free-Vector-Images on Pixabay

There are lots of things going on inside a cell. The DNA is there inside the Nucleus.

In our experiment we will use washing up liquid to explode the cell and help the DNA to spill out and salt will help us to trap it. To see the DNA we will add a liquid called ethanol, DNA is not soluble in ethanol so it will precipitate.

You Will Need

• A banana (or an alternative fruit such as strawberries, kiwi or tomatoes)
• Salt
• Washing-up liquid
• Methylated spirit (or a high-proof spirit such as vodka)
• A beaker
• Sandwich bag
• Spoon
• A measuring Jug
• A sieve lined with paper towel

The Experiment

You can download the worksheet for the experiment here and check-out the video at the bottom of the page for step-by-step instructions or download them here. Want to know more about the words highlighted in red, take a look here.

Methylated Spirit is extremely flammable, make sure you have a responsible adult with you to help with the experiment and follow any safety advice on the bottle, you can see a risk assessment here.

Place the methylated spirit in a freezer or a bowl of ice so it gets really cold whilst you begin the rest of the experiment. Warning: Most freezers are not spark-proof, if placing in the freezer, make sure the methylated spirit is in a vapour-tight container with the lid tightly closed to prevent the release of flammable vapours. For a safer-alternative place in a bowl of ice.

 

To make the extraction mixture:

1. Add 1 teaspoon of salt and 2 teaspoons of washing up liquid to 100 mL water.
2. Gently stir the mixture until the salt dissolves.

To extract the DNA:

1. Add a small portion of banana (or an alternative fruit) to a sandwich bag and carefully pour in 50 mL of the extraction mixture, seal the bag (make sure you remove as much as the air as possible so the bag doesn’t burst!)
2. Mash the banana into really small pieces; this is breaking down the cells releasing the DNA.
3. Filter the mixture through a sieve lined with paper towel to remove any lumps of fruit.

To precipitate DNA (Make sure you get an adult to help you with this part!)

1. Collect your cold methylated spirit.
2. Carefully add approximately 1 cm of methylated spirit (or alternative alcohol solution) to the top of your filtered solution.
3. You should see a white solid form between the two layers – this is DNA!!
4. You can use a cocktail stick or tweezers to remove the solid, look closely what does it look like?
5. Make a note of all your observations on the worksheet.

Going further

Learning scientific words:

DNA – Stands for DeoxyriboNucleic Acid.

Extraction mixture – We call it an extraction mixture because you are removing (or extracting) the DNA from the cell.

Methylated Spirit – Methylated spirit is largely made up of ethanol, DNA is not soluble in ethanol.

Precipitate – When something goes from in a solution to a solid.

Salt – Chemists call this NaCl.

Solution – A solution contains one thing dissolved in another. For example, a salt solution is made up of salt dissolved in water.

Water – Chemists call this H₂O.

What Scientists do:

DNA can be extracted from your hair or saliva and is unique to each individual (refer back to the worksheet, exercise one) children may look similar to their parents but they are not identical. A group of scientists called forensic scientists can use DNA, collected at a crime scene, to work out who committed the crime.

In Professor Rachel O’Reilly‘s group, at the University of Birmingham, we use some of the really special properties of DNA to make new synthetic materials.

 

Curriculum

From Y6 children should be learning to;

• recognise that living things have changed over time and that fossils provide information about living things that inhabited the Earth millions of years ago
• recognise that living things produce offspring of the same kind, but normally offspring vary and are not identical to their parents
• identify how animals and plants are adapted to suit their environment in different ways and that adaptation may lead to evolution

While pupils at this age are not expected to understand how genes and chromosomes work, many pupils will be aware, to some extent, of DNA.

 

This work is licensed under a Creative Commons Attribution 4.0 International License.