Download VGEC: Teacher Notes Go Bananas!

VGEC: Teacher Notes
Go Bananas!
A simple laboratory practical in which DNA is extracted from bananas using everyday chemicals.
DNA is the chemical genes are made from. It contains a code that specifies the amino acid sequences of
proteins. Proteins do jobs within cells, and the proteins a cell makes determine what type of cell it becomes
(a liver cell, a muscle cell, and so on).
A gene is a length of DNA that codes for a specific protein. Genes form a recipe for living things, and are
passed from generation to generation.
Intended learning outcomes
That DNA is contained within all living things.
That DNA can be extracted from living things using simple household chemicals.
That living things contain large amounts of DNA.
Possible curriculum links
Key Stage 3: 2.1 Practical and enquiry skills
Key Stage 4: 5c Organisms and health
Files provided
1 Banana Teacher Notes. docx/rtf/pdf
This document – includes Teacher Notes and Student Handout.
2 BananaPoster.pptx/pdf
A poster to accompany the activity (optional).
3. Banana Slides .pptx/pdf
Slides to accompany the activity (optional).
Key vocabulary
DNA (short for deoxyribonucleic acid): the material from which genes are made.
Extraction: the process of removing a substance from a mixture of other things.
Precipitate: a solid substance separated from a solution by physical or chemical change.
Answers to questions on Student Handout
Describe the DNA you extracted. What did it look like?
The DNA looks like white cotton wool. This is because, like cotton wool, DNA consists of many small fibres.
Describe the role of the main steps in the process of DNA extraction: crushing, salt solution, washing-up
liquid and ethanol.
Virtual Genetics Education Centre: http://www.le.ac.uk/genetics/genie/vgec/
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The crushing breaks down the plant cell walls; the salt solution makes the DNA strands stick together; the
washing-up liquid breaks down the cell and nuclear membranes; and the ethanol brings the DNA out of
solution.
Could you use the same technique to extract DNA from other plant materials?
Yes. All living things contain DNA.
Procedure [and notes]
Start by reviewing the process with the students. Stress the importance of following the protocol carefully.
1
Weigh out about 10 g of banana.
Banana that is ripe, or just past ripe, works best. The point can be made that decomposition starts to break
down the cells. If a balance is not available, use 2 to 3 cm of banana.
2
Mash it with a mortar and pestle.
This breaks down the tough walls of the plant cells to release the cell contents. (If a blender is used, mix the
banana with a little water.)
3
Put the banana mash into a plastic tube.
4
Add 12 ml of salt solution using a measuring cylinder.
The salt solution helps the DNA to aggregate (clump together).
5
Add 1.5 ml of washing-up liquid using a plastic pipette.
The washing up liquid dissolves the lipids in the cell and nuclear membranes, releasing the DNA into the
salt solution.
6
Replace lid and shake well.
7
Put a filter in a funnel – and put the funnel into a beaker.
Students may need to see this demonstrated.
8
Filter the banana mash.
This removes the cell debris and banana pulp.
9
Suck up filtered liquid using a plastic pipette (about 5 ml).
10 Put this liquid into a clean plastic tube.
11 CAREFULLY dribble an EQUAL volume of cold ethanol down the side to form a layer on top of the
banana fluid.
This is the important step, and must be demonstrated to the students. Hold the tube at an angle, and
carefully run the alcohol down the side to form a separate layer on top of the banana solution. A plastic
pipette may help. Don’t mix the alcohol and banana solution. Add about the same amount of alcohol as
banana fluid.
Ice-cold 100% ethanol works best: perhaps because the temperature gradient helps the DNA to precipitate.
12 Replace the lid and GENTLY swirl the tube a few times.
13 Look at where the two layers meet …
DNA is not soluble in alcohol, so it precipitates out while the remaining material remains in solution. The
process may take a few minutes to complete, although the students should be able to see something fairly
quickly.
The DNA looks like ‘white cotton wool’. It can be explained that, like cotton wool, the extracted DNA is
composed of many small fibres.
Virtual Genetics Education Centre: http://www.le.ac.uk/genetics/genie/vgec/
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Materials
Bananas – well past ripe if possible
Mortar and pestle
Clear plastic tubes
Plastic pipettes
Plastic funnels and filter papers (white coffee filter papers work well)
Plastic beakers
Measuring cylinders
Salt solution (approximately 30g per litre of normal cooking salt)
Ice-cold 100% ethanol (in ice buckets or from the freezer)
Washing-up liquid (diluted 1:5)
Optional
Lab coats and plastic gloves (the process can be messy!)
Balances for weighing banana
Mats for cutting bananas
Plastic knives / spoons
Petri dishes for carrying banana
Virtual Genetics Education Centre: http://www.le.ac.uk/genetics/genie/vgec/
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VGEC: Student Notes
Go Bananas!
1
Weigh out about 10 g of banana.
2
Mash it with a mortar and pestle.
3
Put the banana mash into a plastic tube.
4
Add 12 ml of salt solution using a measuring cylinder.
5
Add 1.5 ml of washing-up liquid using a plastic pipette.
6
Replace lid and shake well.
7
Put a filter in a funnel – and put the funnel into a beaker.
8
Filter the banana mash.
9
Suck up filtered liquid using a plastic pipette (about 5 ml).
10
Put this liquid into a clean plastic tube.
11
CAREFULLY dribble an EQUAL volume of cold ethanol down the side to form a layer on top of the
banana fluid.
12
Replace the lid and GENTLY swirl the tube a few times.
13
Look at where the two layers meet …
Questions
Describe the DNA you extracted. What did it look like?
Describe the role of the main steps in the process of DNA extraction: crushing, salt solution, washing-up
liquid and ethanol.
Could you use the same technique to extract DNA from other plant materials?
Virtual Genetics Education Centre: http://www.le.ac.uk/ge/genie/vgec/