STEM Lesson Title: DNA Extraction Lab
Objective: The purpose of this lab is to extract DNA from various tissues. For many students,
DNA is a very abstract concept. This activity will bring about a better understanding that DNA is
a physical substance found in the cells of all living things. DNA is a double stranded molecule
that is composed of nucleotide bases which determines trait and codes for proteins. It can be
extracted from plant and animal cells using the following method and seen easily with the naked
eye.
Bloom’s Taxonomy Framework
Knowledge
Remember
Dimension
Factual
Conceptual
Procedural
Metacognitive
Understand
Apply
Analyze
Evaluate
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Create
DNA Extraction from Strawberries
Essential Question: Why are strawberries a good tissue for extracting DNA?
Student Materials/Resources
Strawberries (fresh or frozen)
Crushed ice/container
Freezer quality zip lock baggie
Extraction buffer
Cheesecloth or coffee filter
100ml beaker
Pipette
Ethanol (cold)
Test tube
Rubber band
10 ml graduated cylinder
Wooden coffee stirrer
Lesson Plan
Procedures:
1. Place a piece of fruit in a zip lock baggie.
2. Smash with fist for two minutes.
3. Add 10 ml of tissue extraction buffer to mixture in baggie.
4. Smash again for one minute.
5. Secure piece of cheesecloth or filter paper over the top of the beaker with the rubber band
and filter the strawberry mixture through the cheesecloth (or filter paper).
6. Pour the filtrate into the test tube until the test tube is ¼ full.
7. Slowly pipette the cold ethanol (that has been sitting on ice) into the test tube (until ½
full) to form two layers.
8. At the interface of the two layers, you will see the DNA precipitate out of the solution.
Carefully spool the DNA onto the wooden stirring rod.
Mammalian DNA Extraction
Essential Question: Why is testicular tissue a good specimen for extracting DNA?
Student Materials/Resources
Testes (fresh or frozen)
Crushed ice
Mortar and pestle (on ice)
Extraction buffer (cold)
SDS (sodium dodecyl sulfate)
Pipet
Test tube
2M NaCl (cold)
Ethanol (cold)
Centrifuge
Centrifuge tube/cap
10 ml graduated cylinder
Stirring rod
Microcentrifuge tube
Lesson Plan
Procedures:
1. Obtain a small piece of tissue (about 2-3mm ) and place it in the mortar sitting on ice.
2. Add 1 ml of extraction buffer (cold) and 3 drops of SDS to the mortar containing the
tissue. Grind the tissue with the pestle. Always keep the mortar on ice. Be careful not to
let the ice melt into the mixture.
3. Transfer the entire slurry into the centrifuge tube and add twice the volume of NaCl
(cold).
4. Cap and shake the tube for two minutes.
5. Centrifuge the tube for 7 minutes (do not operate unless under the direct supervision of
the teacher because the machine must be balanced).
6. After centrifuging, there will be two layers: a bottom precipitate pellet and an upper
liquid supernatant containing the DNA. Carefully pipette the upper aqueous layer into a
test tube – do not stir up the bottom layer!
7. Hold the test tube containing the DNA supernatant at a 45 degree angle and slowly add
the cold ethanol to form a top layer.
8. Carefully spool the DNA onto the stirring rod and transfer it to the micro centrifuge tube.
Safety Precautions: Wear safety goggles and never have food or drink in activity area.
Teacher Materials/Resources: Since testicular tissue has a high nucleus to cytoplasm ratio, this
tissue yields a high amount of DNA. Contact your local spay and neuter clinic in advance to
obtain specimen.
Solutions:
Extraction Buffer (for strawberry DNA extraction): Combine 50ml liquid dishwashing detergent
and 15g NaCl diluted with 950 ml water.
Extraction Buffer (for mammalian DNA extraction): Combine .87g NaCl and 10 mls of 0.1
EDTA (ethylenediamine tetraacetic acid) diluted to 100 ml with distilled water.
SDS (sodium dodecyl sulfate) – 15% Solution
Lesson Extensions/Assessments
-Experiment with different types of tissues (banana, onion, even human cheek cells)
-Experiment with different concentrations of salt and detergent
Adapted from Berry Full of DNA by Diane Sweeny for Biology: Exploring Life by Prentice Hall